- 3 months ago
How does your motorcycle exhaust system help your engine make more power, be more efficient, and sound amazing? Like many parts of the motorcycle, there are near-infinite variations. For exhaust systems Technical Editor Kevin Cameron and Editor-in-Chief Mark Hoyer discuss: length and diameter of the tubing, collector size and shape, how long each element of the system is, overall length, silencer type, cam design, port length and shape, cylinder grouping, and so much more. We get into four-into-one vs. four-two-one, the "power bulge," what is reversion, stepped headers and, well, like we said, so much more. Join us!
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SportsTranscript
00:00:00The Cycle World Podcast is back. I'm Mark Hoyer, the Editor-in-Chief, and I'm with Kevin Cameron, our Technical Editor.
00:00:06Today we're going to talk about the mystery of exhaust pipes.
00:00:10Four-stroke. We've done a two-stroke expansion chamber podcast. We're talking four-strokes.
00:00:16What kind of organ are we playing here anyways, you know?
00:00:21Kevin's going to talk about pulse waves and all these things.
00:00:24That's what we'll get into and why the stuff worked and where it came from.
00:00:30I've always been fascinated by construction of exhaust systems, and I've changed a few in my day.
00:00:39I've had wonderful results. I think my best results were the 1975 Leverda 3CL.
00:00:45It's a 1,000cc, 180-degree triple.
00:00:49It had the stock LaFranconi exhaust system on it.
00:00:53Nice-looking header pipes fit just fine, but the collector was the size of a straw.
00:00:58So, a triple just goes three into one, typically, and that's what it did.
00:01:04It went three into a very small collector and then had these kind of beautiful kind of megaphone-shaped mufflers,
00:01:09but they had outlets on them that were tiny.
00:01:13And that 1,000cc motorcycle, Thoroughbred Italian, made 55 horsepower on our rear-wheel dyno.
00:01:20And, you know, it ran okay. It was fine.
00:01:24I had Del Ordo carburetors.
00:01:26I ordered a fabulously expensive exhaust system made out of stainless steel from a company called Keyhan.
00:01:33Not Keyhan like carburetors, but Keyhan in England from the late Lance Weil, who was a Leverda person.
00:01:40Oh, yeah.
00:01:41Ricky, Ricky racer.
00:01:42The late Lance Weil, because he left the chuck in his lathe, and unfortunately, it struck him and ended Lance Weil.
00:01:53So, be careful with your chucks and your lathe.
00:01:55Mine's on a springy chain thing.
00:01:58A springy chain.
00:01:59I keep finding it in the three-jaw, and I take it out and put it on the table.
00:02:06And the next time I look, there it is.
00:02:08It's just sticking out.
00:02:10I didn't know that he took that hit.
00:02:13That was a terrible thing.
00:02:14Yep.
00:02:15Lathe safety.
00:02:16Cyborg World podcast, indeed.
00:02:18So, be careful with your machines.
00:02:20In any case, Lance sold me this system.
00:02:23It was fabulously expensive.
00:02:24I put it on.
00:02:25The jetting was wrong.
00:02:27Ron Wood's shop was just blocks away from our Newport Beach office, where our dyno was.
00:02:31And Elliot at Ron Wood Racing, who was doing a lot of the work, you know, taking orders, being on the phone, checking stock, put me on the Del Ordo carburetor needle exchange program, as I called it.
00:02:45And I was able to try all the pilots and different cutaways and slides, and I jetted that thing perfectly.
00:02:50I've told the story before because it had an electronic ignition that would switch between 10 and 35 or 10 and 37, whatever it was.
00:02:58And that was an early form of electronic ignition.
00:03:01There was no curve, and it switched over at, like, say, 3,500, and I couldn't figure out why I was getting a misfire at 3,500 when I held it.
00:03:09And it was because it was going between 10 and 35 degrees of advance.
00:03:14But this is an exhaust story.
00:03:15So, I put that key in on, and I jetted for it, and it made 70 horsepower at the rear wheel.
00:03:22So, it was like 50, 55.
00:03:24So, I picked up 15 to 20 horsepower.
00:03:27Not only did you uncork it, but you also arranged for the energy in the exhaust to help fill your cylinders.
00:03:36So, this was wonderful, and over the years, I've had the fortune to, I visited Vance and Hines many years ago when they were in multiple units in Santa Fe Springs where they had started in one, and then they grew, and they took over the next one, and then they took over, and then suddenly they had the whole place.
00:03:54And I toured that with Terry, Terry Vance at the time, and it was just a labyrinth of pipes and jigs, and there were jigs everywhere.
00:04:07And Terry said, we have every, at the time, I don't know what the case is now, but he said, Terry said they had every jig that they'd ever made, and they were, like, hanging from the rafters.
00:04:15They were everywhere, and the polishing operation was, just in general, I've seen many polishing operations, and, you know, back in the dark days, it was like, polishing is gross.
00:04:27When you're doing mechanical polishing on big cotton wheels, and you're using your rouge and all that stuff, it is a disgusting, messy business.
00:04:35So there's this room where the corners of the room are filled with that, and then the guys are all covered with black, and most of them have, like, three fingers or whatever, just from, you know, polishing mistakes.
00:04:50That wasn't really necessarily Vance's shop, it was just, in general, I've been to a bunch of polishing operations.
00:04:55So the pipe-making business, when we get these pristine, beautiful systems, like you see in a Kropovich system, you think, that was made in a surgical theater.
00:05:06Clean room, yeah.
00:05:07Clean room, just exquisite, and we appreciate that very much, with welds that could only be described as perfect.
00:05:18But there's a lot to it, you know.
00:05:19We can do a lot, just changing from our EPA-mandated systems to a racing system, but it's really about the musical instrument, and the pulse wave coming out of the chamber, and then finding something in the exhaust system that turns the pulse wave around.
00:05:41And, you know, you might have, what do you think, 1.2, 1.8 bar, maybe, at the highest pressure, 100 psi?
00:05:51Oh, well, there's the order of 100 psi in the cylinder at the end of a heavily loaded, you know, peak torque stroke.
00:05:59Yeah, so that's your positive wave traveling down, and then it hits something like the collector.
00:06:05And I've been reading that, you know, there's guys out there, David Vizard is one, who's a big...
00:06:11Great name.
00:06:12Great name, engine tuner across V8s and British and all kinds of stuff, and he's very hyped up on the secondary and how the secondary has some real effect.
00:06:26In any case, it comes back as a negative wave, and I'll let Kevin ride the negative wave and tell us what's up.
00:06:33Well, in earliest times, people didn't see a need in racing to have any exhaust system.
00:06:45So you've probably seen the dramatic videos of the Beast of Turin, the 1910 Fiat S76, being started with a crank.
00:06:56This is a 21-liter engine.
00:07:01Would you try to turn such a thing?
00:07:04Oh, what's the compression?
00:07:06Come on.
00:07:07Well, the compression is pretty small.
00:07:09It's true.
00:07:10But when it comes to manly efforts, you see tiny men pushing 500 Nortons down Bray Hill, trying to start them.
00:07:19Good luck, fellows.
00:07:20All of us.
00:07:21Just a tip for hand cranking in any car engine.
00:07:25I've had a few that I have started with hand cranks.
00:07:28Is you don't hook the crank with your thumb.
00:07:31Leave it out in case it kicks back so it doesn't take your thumb off.
00:07:35Just a tip from the past.
00:07:37So it had just stubs.
00:07:42And when it fires, fire comes out.
00:07:45Yeah, fire.
00:07:46It's firing.
00:07:48And you can see it.
00:07:50And Harley's board track racers, the four valves, just had stubs sticking out.
00:07:58And this was considered radical and all you need.
00:08:06Whereas many racing cars very shortly later had demure exhaust systems that collected it all and fed it out the back of the car.
00:08:18Well, the motorcycle thing, it was discovered pretty quickly, whether it was on a dyno or whether it was at the Great Brooklands Speedway, which opened south of London in 1907 and promptly attracted 1,000 monkeys at 1,000 typewriters.
00:08:42One of the best ways to research anything is to do the Bell Labs approach.
00:08:48You have all these people who are fascinated by the problem they're working on.
00:08:52And you just set them loose.
00:08:54Tell them lunch, breakfast, dinner, it's on us.
00:08:58Go for it.
00:08:59The 1986 GSXR 750 effect.
00:09:03Development across thousands of enthusiasts who just got a win.
00:09:08Yep.
00:09:09You got it.
00:09:10So, and we used to see the porting that all these people had done when I was doing Suzuki Cup Tech years and years ago.
00:09:20But it was discovered that not only did a length of pipe on the exhaust bleed the horrible smoke out of the dyno shop or to the rear of the motorcycle so that you didn't have to recycle it personally.
00:09:37Unfortunately, there seemed to be a relationship between length of pipe and engine performance.
00:09:45So, people bore down on that.
00:09:48And soon they had rules of thumb for pipe length.
00:09:53And, of course, you can find all that stuff on the Internet.
00:09:56Diameters, pipe lengths, where to locate this or that junction.
00:10:00But, of course, here's what was happening.
00:10:04The pulse comes out positive.
00:10:07It goes down the pipe.
00:10:09It gets to the end where suddenly it expands in all directions, including back up the pipe.
00:10:16A negative wave propagates up the pipe.
00:10:19And when it gets to the cylinder, gets to the exhaust port, it pulls some of what's above the piston at top dead center out of there.
00:10:32And this was step one, the relationship between pipe length and engine torque.
00:10:41Step two, the big discovery came in 1912, and it may have come earlier in auto racing, of valve overlap.
00:10:53So, a very young Vic horseman, who later was a kingpin in British tuning, this is 1912, was playing with different timings.
00:11:09And he wanted a certain timing.
00:11:11So, he decided with the Singer engine that he was working with to switch the intake and the exhaust cams.
00:11:20And however it was that he timed them, he got an improvement.
00:11:25And he talked to his mentor and indicated that this looked promising.
00:11:36And the mentor looked into it.
00:11:39Oh, George Stanley, right?
00:11:42Yeah, George Stanley.
00:11:43And valve overlap is that period near top dead center at the end of the exhaust stroke,
00:11:54in which the exhaust valve has not yet completely closed.
00:12:00And the intake valve is beginning to open slightly before top dead center.
00:12:06Now, why would you close the exhaust late, open the intake early?
00:12:11Well, because you wanted to position maximum valve lift where it could do the most good on the intake side, for example.
00:12:20And people had all kinds of theories about how these things either worked or ought to work.
00:12:28So, they discovered that pipe length and valve overlap were synergistic.
00:12:37And the great thing that it did was when that returning low pressure wave arrived at the exhaust port during the overlap period,
00:12:51not only could it pull some of the residual exhaust gas above the piston out of there,
00:13:01but the low pressure that it created in the combustion chamber caused fresh charge to begin blowing in through the intake valve,
00:13:12which was just starting to lift.
00:13:14The piston is sitting there at top dead center, kind of going, tapping on the table with its fingertips.
00:13:21Now, we're waiting for orders here.
00:13:26And so, this starts the intake stroke early.
00:13:31It starts flowing fresh charge into the combustion chamber before the piston has even begun its intake stroke.
00:13:39Well, during the 1920s and 30s, the between-the-wars era,
00:13:47the synergism between pipe length and overlap was developed to an enormous degree,
00:13:56which we'll go into presently.
00:14:01But the basics of it are that when you have a little bit of overlap,
00:14:07one of these is the exhaust, the other is the intake,
00:14:10you can scissor the cams to increase the overlap.
00:14:16And that increases the effect.
00:14:21And it broadens the number of RPM over which the effect can take place.
00:14:27Well, another thing began to occur to people.
00:14:35This pipe looks small.
00:14:37Let's put on a great big one.
00:14:38Well, it didn't help.
00:14:43What if we made the pipe in two pieces?
00:14:45We'll put regular-sized pipe out the port,
00:14:49and then we'll fit a pipe an eighth of an inch bigger over it downstream somewhere.
00:14:58Well, there was a little gain,
00:15:03whether it was seen on the tachometer while bumping and crashing along Brooklyn's terrible pavement
00:15:13or in the dino shack.
00:15:17And people generalized this idea.
00:15:20This is the great thing about the thousand monkeys.
00:15:22And I don't mean anything pejorative
00:15:24by comparing very numerous researchers
00:15:30working privately to the group of monkeys in the classic example.
00:15:36It's simply that we've all heard that line.
00:15:43Finally, you know, somebody runs in from the huge typing pool
00:15:47where they're all furiously typing and says,
00:15:49come on, come down here.
00:15:50You've got to see this.
00:15:51One of the monkeys is just steadily typing out Shakespeare entirely by accident.
00:15:58Well, the Shakespeare that was typed next was someone said,
00:16:04well, if two or three of these steps work better to produce some effect,
00:16:13let's call it an extractor effect.
00:16:16Now, of course, a low pressure doesn't suck fresh charge in.
00:16:21It takes the obstacles to the fresh charge away.
00:16:25It pulls a partial vacuum.
00:16:27And then the fresh charge behind the intake valve has no choice.
00:16:31It has to go there.
00:16:32But these people reasoned thusly.
00:16:36If many steps give a good effect, what about a continuous enlargement?
00:16:42And they built the megaphone.
00:16:47And people tried extending the taper all the way back to the exhaust port.
00:16:54And it did not work.
00:16:56In fact, if they extended it too far upstream, it didn't work either.
00:17:03So the megaphone became something between 8 and 12 inches, maybe 14 at the outside long,
00:17:10at the end of the plane header pipe.
00:17:14Now, what the megaphone does is instead of the one sudden low pressure off the open end of a plane pipe,
00:17:25you have enlargement going over a period of numerous microseconds.
00:17:33And it didn't take long for the angle of the megaphone and the ratio between the plane pipe and the megaphone outlet that that's what dinos are for.
00:17:45That's what Brooklands was for.
00:17:47Lots of people trying lots of things.
00:17:50So what came of this was conditioned by where motorcycles were going from Brooklands, the Isle of Man.
00:18:05The Isle of Man is not a racetrack that requires that your engine should pull strongly from down here all the way up here.
00:18:15So when they found something disagreeable about valve overlap combined with a tapered megaphone,
00:18:27they weren't too sad about it.
00:18:31But here's what they discovered.
00:18:33They discovered that in the exhaust pipe, it isn't just the pressure pulse that comes out and the negative wave that comes back.
00:18:41Because like an organ pipe, positive and negative waves are bouncing back and forth between the ends continuously.
00:18:51So that means that right behind the negative wave that helps torque by starting the intake function earlier, there's a positive wave.
00:19:04And when the positive wave, when your engine is turning at low enough RPM that the positive wave is the one that arrives at the exhaust port during overlap.
00:19:17It blows extra exhaust back into the combustion chamber through the intake valve, upstream through the carburetor.
00:19:26And if there's an airbox, it may make a fair start on filling it.
00:19:32So you have incombustible exhaust gas everywhere.
00:19:37It will not support combustion.
00:19:42And so that delays the intake stroke.
00:19:46So these things produce a flat spot.
00:19:49A place where there's low torque over a few hundred RPM.
00:19:56Well, they want to investigate this terrible thing.
00:19:59This is spoiling the party.
00:20:00We just, when we've got, we've got the plan for enhancing power for practically nothing but an afternoon of welding and fitting.
00:20:11Comes a dreadful flat spot.
00:20:13Well, one of the things they found was that the engine was very rich in the flat spot.
00:20:23And decades later, when people had their first super flow dyno and they put their four into one equipped four cylinder super bike on the thing and they mapped out what was happening.
00:20:36They saw this beautiful torque, but they also saw a dreadful flat spot.
00:20:42And it was dreadful because if you have to pass through the transition from the flat spot to peak torque, the torque rises out of the hole steeply to the peak.
00:20:58And if that rise occurs while you're trying to accelerate off a corner with your rear tire at or near its limit of adhesion, you're going in the gravel.
00:21:13So flat spot had to go in super bike because those great big engines could throw you farther than the little 350s and 500s of the between the wars era.
00:21:26So what did they do?
00:21:28They arranged to run the engine above the flat spot.
00:21:36And that is why the flat spot is what people used to call megaphone-itis.
00:21:43Once you made your engine dependent upon this for its power by, one, having a camshaft with large overlap, racing stuff, big cams, and two, you had an extractor exhaust pipe with a megaphone on the end,
00:22:03you would have this problem that you couldn't give your engine full throttle, say a 7,000 RPM Norton-Manks single below 55, 5,800 RPM because it would, the waves and the carburetor didn't know what to do.
00:22:22So when the fuel stuff comes, exhaust gas comes rushing through the carburetor in the wrong direction, the carburetor adds fuel to it.
00:22:32Then the intake stroke starts and that inert gas loaded with fuel now is drawn through the carburetor a second time and picks up fuel for a second time.
00:22:44So it is, as my dad used to say when he was a short order server, double rich.
00:22:51And that also made your engine into a sluggard below, in this flat spot region.
00:23:05So the trick to making a fast lap at the Isle of Man is to keep your engine off of that place and run it above.
00:23:15And one weekend at Loudoun racetrack, my rider, Rich Schlachter, managed to beat Mike Baldwin.
00:23:29And we thought, oh, we're on our way.
00:23:32We're getting someplace at last.
00:23:34The next club weekend, Mike blew us in the weeds.
00:23:39He just left and he didn't dignify it by ever looking back.
00:23:45Then he came and told us how he'd done it.
00:23:51He said, I just kept the thing above 9,300 the whole time.
00:23:57So I was never upset by the torque step.
00:24:01This is talking about a two stroke, but two stroke and four stroke, when they become dependent upon pipe action, as Muzzy, Rob Muzzy once said, the harder you tune on a four stroke, the more it acts like a two stroke.
00:24:15So riding above the flat spot or the transition is not necessarily easy, but it saves you from that region where torque is increasing so fast that it can trick you.
00:24:35So we end up with this type of engine that does not have a broad torque range.
00:24:45The Manx had a range of 1,200, maybe 1,500 RPM.
00:24:50And that was it.
00:24:53No tractoring off of corners from 4,000.
00:24:56Forget it.
00:24:57Because double, triple carburation is making it too rich to burn.
00:25:03And all that exhaust gas being forced into your intake system and then being inhaled into the cylinder as if it were pure, sweet fuel air mixture.
00:25:17There's nothing good down there.
00:25:20Nothing you'd want.
00:25:21So that was the state of the single cylinder art.
00:25:29And when Honda in the 1960s won so many Grand Prix championships in 50, 125, 250, 350, they never won one in 500 because Agostini was there.
00:25:44But all of those engines had long taper megaphones, which gave them a pretty fair spread of power, making those four strokes easier to ride than, say, Phil Reed's Yamaha at that time.
00:26:04This is the 1960s.
00:26:06So we get to the present day.
00:26:08I made a practice when I used to go to Daytona of walking around the garages to see what's up.
00:26:19And this one year, I'm looking, I'm looking, but I don't find a single four into one smokestack.
00:26:28Not one, not in any garage.
00:26:31What I saw instead was four into two into one pipes.
00:26:40How did those come into being and how do they work?
00:26:44Well, I got a phone call from Mark Domek.
00:26:49And he said, he said, basically the equivalent of, man, you got to help me because all these people bought superflow dinos and they all discovered the flat spot and they tried to jet out of it and they couldn't.
00:27:06And they tried everything and nothing worked and they, because the dino had shown them that this problem existed, they hated it.
00:27:19And they called Mark Domek and said, your dinos are no good because they, they're showing this, this terrible thing happening.
00:27:28It would fix it.
00:27:30So Mark said, would you, would you please write a short, but clear and persuasive description of how the flat spot comes to be?
00:27:44So I did that and sent it to him.
00:27:47Anyway, the monkeys got to work.
00:27:50All of the diligent, experienced, willing to try anything, people in the speed industry.
00:27:59And one of them, or maybe it was invented multiple times.
00:28:03Many inventions are invented over and over again.
00:28:07For example, squish.
00:28:09I've counted four inventors.
00:28:12I'll bet there are more.
00:28:13But at any rate, what they said was they're looking at a four into one and these four pipes go down and they join into a collector.
00:28:23And Muzzy had said, as a result of numerous trials, we found that the angle to the center line of each pipe as it joined the collector should be around 30 degrees.
00:28:38The smaller that angle, the smaller that angle, the less crosstalk there is.
00:28:43The greater the angle, the more crosstalk from one header pipe to the others.
00:28:49So it was a compromise, like everything in human existence.
00:28:54Now, somebody said, what if we put an enlargement somewhere along the header pipe?
00:29:03It would, we would time it so that it's negative wave at the lower RPM where the flat spot is active.
00:29:17Time it so that the negative wave from the new pipe junction, the new enlargement, would arrive at the valve on top of the flat spot positive wave and cancel it.
00:29:33And the flat spot would, maybe there'd be something left, but it'd be mostly gone.
00:29:41And so what they began to do was to join pairs of pipes to produce this effect at a certain distance from the valve.
00:29:52And people got on the dyno and they perfected this.
00:29:57And this one year at Daytona, the change was sudden and complete.
00:30:03Four into ones, out.
00:30:05Four to ones, in.
00:30:07So the V8 guys would call a tri-Y.
00:30:10Yeah.
00:30:11And they usually, they're often used on truck exhausts, you know, for efficacy from zero to 4,500, et cetera.
00:30:20But, um, David Visard was, uh, talking about this in one of his videos and said that the, um, he did a bunch of development on the Ford Pinto four-cylinder.
00:30:31He was talking about the way that a four-cylinder is affected by the tri-Y, which is our, our game.
00:30:35And he was doing racing stuff.
00:30:37And he said that, um, a good tri-Y, there were two, two points made, a good, a good 4-2-1 on the Ford cylinder at a two liter or 2.3, whatever that Pinto was that he was running, picked up 30 foot pounds of torque in the mid-range.
00:30:51Yeah.
00:30:53And, uh, that's pretty useful.
00:30:56That's pretty useful.
00:30:57But again, we have to make, we have to make a distinction here.
00:31:00You can do drag racing with a four, four into one.
00:31:04You're, you're not going to be trying to pull off a corner at 6,300 RPM.
00:31:11You're going to bring it up to leaving RPM and watch the tree.
00:31:17Yeah.
00:31:17Drag racing is much less about having options than road racing.
00:31:20Yes.
00:31:20Or motor racing.
00:31:21So it, it, it's a different deal.
00:31:23And on the other hand, in road racing, when, um, the old, uh, maestro, um, oh, his name is coming.
00:31:36Anyway, he, he was building 883, uh, Harleys for the AMAs.
00:31:45Don Tilly, the late, sadly, because I'm sure he had a lot more to say, and I certainly have a lot more to learn.
00:31:57But, uh, he said, and I know I've told you this before, but it's worth hearing again.
00:32:05Them young fellers, he said, they love those big numbers.
00:32:09But I've got to tell you, we won a lot of races with horsepower averaged over the actual range of RPM used.
00:32:20So if you've got a flat spot and you're hung in a corner and everyone's going under you and around you, and some may be even beeping the horn, uh, that is humiliation.
00:32:35And there are ways to avoid that.
00:32:38So, um, well, it's, he, when you're building for a range of RPM, you have to be careful to make the shape of the torque curve, something that your rear tire can use and something that your reflexes can keep up with.
00:32:58So, uh, when, when, uh, MotoGP began with 990cc, um, engines, it was promptly possible to knock yourself down if you didn't have a usable torque curve.
00:33:18And in fact, when Honda were developing their MotoGP bike, the RC211V, they gave the prototype engines to test riders and the test riders on a scale of 1 to 10 rated them 2.
00:33:412.
00:33:432.
00:33:45Basically, an unmentionable word.
00:33:50Consequently, someone on the team said, well, what about back when we were thinking about building that 904, uh, Fireblade?
00:34:01We decided that maybe the public weren't ready for a big motor in a light motorcycle.
00:34:11Well, and we hit on the idea of creating a rideability index.
00:34:19And they developed engines on the rideability index.
00:34:24And everybody loved it.
00:34:26And I use the term everybody advisedly because when they gave the high rideability engine to professional road racers, they loved it.
00:34:37The fact that race engines in the past have been finicky and terrible problems with, oh, the sun went behind a cloud.
00:34:50Where are all the jets?
00:34:51Where are the needles?
00:34:52Those were problems, not necessary qualities.
00:35:00But it's possible for humans to decide, oh, this engine's really hard to ride.
00:35:05It must be hot.
00:35:06No, it's junk because you can't ride it.
00:35:10So they apply.
00:35:11Yeah, so many times the abrupt power ban makes less power.
00:35:16It gets your attention, though.
00:35:18But you think it's amazing because, oh, this comes on way, this comes on way stronger.
00:35:23And it's like, no, actually, it's really bad.
00:35:25It's just, it has less and it comes on and it's distracting and you can't manage the traction and all that business happens.
00:35:33So I suspect that they applied the rideability index to the prototype RC211V, which is a V5.
00:35:43And they were able to civilize it.
00:35:46So the rideability index, the large project leader of the CBR900RR, Tadao Baba.
00:35:54Yes, Mr. Baba.
00:35:55Mr. Baba.
00:35:57They had, you know, a chart.
00:36:00And over here was tractability and this was, you know, a lightness.
00:36:04And his guidance was make a bigger circle.
00:36:09Yeah.
00:36:09That's what he wanted, bigger circle.
00:36:11And that's our average torque over the range we're using.
00:36:18And that's, David Vizard will relentlessly hammer that.
00:36:22And he should.
00:36:23Look at these numbers.
00:36:25Forget about that one way up there.
00:36:27Look at these numbers because we'll go back to basics.
00:36:30A 14-turn racetrack with two long straightaways.
00:36:33Do you want to take advantage of a tenth of a second 14 times or of half of a tenth?
00:36:40Or do you want to gain a little bit at the end of two straightaways when you've got to brake hard?
00:36:45And have to brake earlier, yes.
00:36:48Making the straightaways shorter.
00:36:50I mean, it's all a fine balance, right?
00:36:53And that's what's so beautiful about racing is that it's never any straightaway.
00:36:55But the reason that we mention this is that it's a temptation to imagine that being hard to ride means that your bike is hot.
00:37:06And that, well, just this craziness of thinking that because the difficulty with the engine has historically been a part of racing,
00:37:26progress has been made and we don't have to put up with that anymore.
00:37:30So, the 4-2-1 is universally used now in any application requiring a broad range engine.
00:37:50And during the crisis, when the flat spot was discovered and what are we going to do about it?
00:37:57Things like crossover tubes and resonators and what have you were also being discovered.
00:38:04A crossover tube can give the pulse two pathways, one longer and one shorter, which can have a power broadening, a torque broadening effect.
00:38:16And a resonator could conceivably gobble up the positive wave long enough for the exhaust valve to close so that bad effects didn't reach the cylinder.
00:38:33Well, this WR-250 of mine back here, if you can peek right past the microphone, has a little resonator in the head pipe.
00:38:46And they always talk about that as the power bulge.
00:38:49I don't know, man.
00:38:51It's waves.
00:38:52It's interesting to look at modern exhaust systems.
00:38:54You know, when you go out to your Akrapovic, all the factory systems are really nicely made.
00:38:58To get a gain in the aftermarket, the first thing that you get from an aftermarket exhaust system is lighter weight.
00:39:04Typically, you get it.
00:39:05Oh, man.
00:39:06You just lose pounds.
00:39:07And it's nice.
00:39:09These people handed me a titanium system.
00:39:12It's got the muffler on it.
00:39:13It's for a super bike.
00:39:14It's got to have a muffler.
00:39:15They handed it to me, and it was balsa wood.
00:39:18Yeah, it's like packing material.
00:39:20It's nothing.
00:39:21It was seven pounds.
00:39:23We all know that there are 40-pound systems, because how happy you're going to be with your GSX-R, with its aftermarket pipe, if the thing starts rusting through after 18 months.
00:39:37Unhappy.
00:39:38So how do you fix it?
00:39:40Well, you could pay triple for stainless.
00:39:44Oh, no.
00:39:44I don't think I want to do that.
00:39:45We have plenty of stainless exhaust, but yes.
00:39:49We'll make the mild steel thicker.
00:39:52Yeah.
00:39:52That way, it'll take longer to rust through.
00:39:55Well, but yeah, seven pounds, that's what I want.
00:39:59Thou shalt be rich, was engraved on the tablet that Moses dropped and broke on his way down the mountain from his interview.
00:40:10Had it not been for that, we would all be able to afford all this beautiful hardware for racing.
00:40:18Well, you go, you know, I wanted to see what the latest offering from a Kravitz was for a BMW M1000RR and an S1000RR.
00:40:28And, you know, years ago, there was a, I didn't see any on the site this time, but there was a system that they were making for a while that was like shaped like a Cobra.
00:40:35So it would come out of the port and then the tube would flatten out and it really looked like a Cobra ready to strike.
00:40:42Yes, with that broad hood that they had on.
00:40:45And it was like, you brought up Kenny Augustine when we talked about this, about raising, this is perhaps an extension of the notion of raising the exhaust floor.
00:40:55Making it flat, in fact.
00:40:57Making it flat so that you didn't get an area of the pipe that was basically not functioning through turbulence.
00:41:02What happens when you make a flow go around a sharp end in a circular geometry pipe is that you get secondary flows.
00:41:13The flow that's high speed goes to the outside and all this other action goes on on the inside where the low energy gas is.
00:41:22So, Kenny made headers that had a tongue sticking out of the engine end of each head pipe.
00:41:35It went into the exhaust port and filled in the floor without having to have your head welded and heat treated and people grinding on it and never being able to get it back.
00:41:49Oh, this was one of Kenny's problems.
00:41:55Just that tongue came in the box.
00:41:59A lovely thing.
00:42:01You know, if you think about the sudden rise in pressure when the exhaust valve opens, the sudden rise in pressure in the exhaust pipe and that hundred something PSI in the cylinder rushing to get out.
00:42:12We don't have any of the intake problems where the air is dense and it's also got a secondary thing in it, fuel, which has a much higher density.
00:42:21Yeah.
00:42:22So.
00:42:22Six or three times.
00:42:24Yeah.
00:42:24So you can, you know, hard turns on the intake are a little bit different than hard turns in the exhaust only because the exhaust gas is hot.
00:42:32Like we don't want to get that into the cylinder head, get it into the pipe, get it out of there.
00:42:38But the, just that think about the very first step coming out of the cylinder.
00:42:43If you put the, if you put the turn right there, there's going to be a big difference between having the, having the turn two inches away about what, you know, if you look at a cast iron manifold on an American V8.
00:42:55Those things are often like, let's not, yeah, seriously, but there's just slapped on there and there's no, there's no nothing that it goes out and it hits a wall and it bounces back in.
00:43:06Like you're not going to clear the cylinder out necessarily.
00:43:09That's why even today, American V8 headers to me look like yesterday because there's so many that are just four into one.
00:43:20I mean, they're, they're, the timings are different, but it's a four cylinder and a four cylinder and a zillion of the exhaust pipes, the, the header pipes are four into one.
00:43:29Now there are plenty of, there are plenty of triwise.
00:43:31And then, you know, I was watching, I've been thinking about this quite a bit and I've been looking across the great signal to noise ratio beast called the internet.
00:43:42And I came across this check video on one of the socials and it's these guys speak, I think it's check and there's, you know, they're speaking a language I cannot understand, but they're going on these car exhaust pipes with a rubber spatula, like a rubber spatula.
00:44:00And the guy's like, check it out.
00:44:05And then he goes on and the four cylinders have a different resonance as he's hitting them.
00:44:10And he's like, this is why this guy, you know, subtitles come up.
00:44:13This is why this guy's car doesn't idle right.
00:44:14And it doesn't run right.
00:44:16And so he just casts that aside and he's like, go get Vlad's exhaust system.
00:44:20And it's like an equal length.
00:44:21And he goes, and then he hits them with his spatula and they all sound basically very close to the same note.
00:44:27Yep.
00:44:27But that's only right if the exhaust pulses are perfectly timed, if the engine crank exhaust pulses.
00:44:34So in a V8, you get like one, three, five, and then five, five and seven.
00:44:39So when you hear in a V8 idling, it's kind of going wobble, wobble, wobble.
00:44:42That wobble, wobble is a very, too, very close.
00:44:45They're 90 degrees apart.
00:44:47Yeah.
00:44:48And so if you have an equal length, everybody's like, oh, my headers are equal length and they're only a quarter of an inch apart.
00:44:54This is me quoting David Beisard, by the way.
00:44:56And it's like, no, that's wrong.
00:44:59That five, seven thing needs a different length so that the resonance coming back extracts, does the job it's supposed to.
00:45:07And all these 421s, you look at the S1000RR system I was looking at.
00:45:12You go out, the initial bend and first pipe is straight, I mean, straight diameter, curving.
00:45:23Then it goes to a short tapered cone that's a few inches from the port.
00:45:28Then it goes to a larger diameter.
00:45:31There's a crossover between one and two and three and four, just a small one that's, you know, a quarter to a third the diameter of those larger header pipes.
00:45:42Then it goes down and hits the collector, the two collector.
00:45:50Yeah.
00:45:50And then there's the other two collector.
00:45:52And then those go into the ones that go into the two collector that goes out to the rest of the system.
00:45:58Now, here's something that you won't find on the Internet, or I couldn't, maybe you can.
00:46:06But at one point during the development of American superbikes, tapered headers came into use.
00:46:13They tapered from the exhaust port at one or two degrees, enough to see.
00:46:23And when I asked Muzzy about that, he said, well, it kind of broadens it out some, I guess.
00:46:32And which could be a code word for mind your own business.
00:46:35Well, how many times have you asked somebody about something, and they're just like, oh, it's just something.
00:46:43I don't know.
00:46:44They just wanted me to try it, and I don't know.
00:46:46And it's like, it is the Holy Grail, but they're just like, it's just something.
00:46:51What's Kel said about Goodyear slicks at Daytona in 1974?
00:46:56People asked him, and he said, oh, it's something that Goodyear's playing with.
00:47:00It was a solid gain in lap time, and he didn't want any company up at the front.
00:47:09Who does?
00:47:10So anyway, this tapered head pipe thing, you will find the following description.
00:47:15It says, as the pipe enlarges, it gradually sends back a signal that helps scavenge the cylinder.
00:47:23This doesn't happen, because during the first part of blowdown, that is, the drop in cylinder pressure from end of the exhaust event, or beginning of top dead center to the beginning of the exhaust event,
00:47:43there's a standing shock in the header pipe, and it tends to go upstream.
00:47:55No signal can penetrate the shock, which tells us that the taper in the pipe is not sending signals upstream because it can't.
00:48:08Therefore, whatever is happening, the benefit from it is downstream.
00:48:17And that's why I thought to myself, oh, remember that chapter in Blair where he talks about wave steepening?
00:48:26Maybe this is medicine against wave steepening.
00:48:32If you could, instead of having all the disturbance behind catching up to the main disturbance at the front and causing a shock,
00:48:41you could broaden out the pressure pulse, and therefore the return low pressure pulse.
00:48:49You'd have a little wider torque band.
00:48:55So, when I saw, this was a big deal in two strokes years ago, tapered header pipes.
00:49:02I saw them first on Yamaha.
00:49:05And I'm thinking about that, and I remembered that there has to be a shock in the exhaust port during blowdown.
00:49:14And that means no message can go upstream, so therefore the purpose of the taper has to be downstream.
00:49:23Either that, or it's just the welder showing off.
00:49:28Well, you know, straight pipes are a lot cheaper than tapers.
00:49:31It sure is.
00:49:34But you could buy them as pressed halves and put them together and weld them.
00:49:41Yeah.
00:49:42I think Yamaha was closing in on three degrees when I stopped looking, or when nobody could afford a TZ250 anymore.
00:49:54Yeah.
00:49:54Well, rollers, that'd be the funny thing about trying to roll that on your sheet metal rollers,
00:50:02that you would need a roller that was whatever your primary, your initial primary had to be.
00:50:07And that's pretty small.
00:50:08My rollers are big.
00:50:10I think they've got to be two and a half or something inch.
00:50:13Good.
00:50:15And it occurs to me that we're playing, the orchestra is a couple of instruments.
00:50:24There's all the instruments on the intake side that are doing their honking.
00:50:29One, the famed Helmholtz resonator.
00:50:32The airbox.
00:50:33Helping the airbox resonate to fill in flat spots.
00:50:39Variable length intakes.
00:50:41Horns that lift off at high RPM.
00:50:44The long horn at low RPM.
00:50:45And then some solenoid says, oh, it's 7,500 or whatever it is.
00:50:50And lifts up.
00:50:52Lifts up.
00:50:53And the horn that's below it gets to be this long.
00:50:56Instead of three inches, it's two inches or it's one inch.
00:50:58Whatever they felt worked.
00:50:59Different length intakes.
00:51:03Some of the ones in the middle because the cylinders are hotter or whatever.
00:51:06There's all kinds of.
00:51:07So there's all that stuff happening on the intake side.
00:51:10It's also talking to the exhaust side through overlap.
00:51:15Yes.
00:51:15And then we're getting to the exhaust system.
00:51:20And so one of the things that I was thinking of is we have doodads like EXIP, Yamaha's gate
00:51:26valve that would drop at the collector.
00:51:29And it occurred.
00:51:30You made a joke one time about, I think it was about two strokes, having like basically
00:51:36like saxophone keys on it to where it would open up a piece of the tone and change the
00:51:42frequency because that's what a saxophone is doing.
00:51:45And we're essentially blowing air through some things with some cones, just like a musical
00:51:49instrument.
00:51:50And then I was thinking, well, you made also the joke about a trombone.
00:51:54Like if you could just have a piece of that exhaust system, you could slide back and forth
00:51:57like a trombone.
00:51:58The outboard racers do it.
00:52:00Oh, see.
00:52:01Because I don't know where the hell we fit that on a motorcycle or, but, you know.
00:52:05Well, on the boat, on an outboard powered hydroplane, it's all behind the engine.
00:52:10It points straight back and pulling your pipe.
00:52:13But the hardest thing is that the engine wants to turn, let's say it's a 250 twin.
00:52:21It wants to turn 12,500.
00:52:24And the boat is sitting still in the start.
00:52:31So if you have this great long pipe, it helps it to get moving and then to rise up and get
00:52:41on the step.
00:52:41So the hull is just sort of skipping along like a throne, a stone thrown by a child.
00:52:49And most of your drag is from the air and the propeller.
00:52:54But yes, that's very common in hydroplane racing.
00:52:59And one year at Daytona, a fellow that I knew showed up with one.
00:53:04And he was so proud of it.
00:53:06All four pipes on his TZ750 were under the engine.
00:53:10And he had this mechanism by which it could, the length could be altered.
00:53:15And of course, it was an additional task for the rider.
00:53:21You can't pull away from me.
00:53:23Watch this.
00:53:26Whoosh.
00:53:27So you have the question of how to combine all of these transient effects because only
00:53:40compression and displacement help your engine at all RPM.
00:53:46All this other wave-based stuff is like the pipe organ that plays one note really well.
00:53:53And if you excite it at other frequencies, it doesn't quite get it.
00:53:58It has some range, but it's a narrow curve like this.
00:54:03And that's the way all of these, the airbox resonance is good for a few hundred revs.
00:54:08The intake length, the, oh, the ram air is, of course, dependent upon your forward velocity.
00:54:17If you're going 160 miles per hour and you can realize the entire gain from ram air on a hundred
00:54:25horsepower engine now becomes 103 horsepower.
00:54:31So how you construct the torque curve depends on the application you have in mind.
00:54:39If you want a killer top end, you can pile all the effects on top of each other.
00:54:45If you want a range or if you've got problems with poor flow at a certain RPM, you might want
00:54:53to put the airbox on that or locate whatever else you have going on that RPM to, to sort
00:55:01of help things along.
00:55:03Well, my ongoing.
00:55:04Yes.
00:55:06Go ahead today.
00:55:07Oh, today valve overlap is going away because, uh, fuel coming in can go out the exhaust where
00:55:20the EPA considers it fair game.
00:55:23You're busted.
00:55:25You're fine is in the mail.
00:55:27So, but what has been done to get around this is that where overlap plus pipe effects can
00:55:39give you this strong torque bulge, the changes that are being made today are toward shorter
00:55:49timing, less overlap, less overlap, scissoring it away to, uh, remember the 11 degree.
00:55:56That was what Ducati engineers referred to the, um, their, what is that big cruiser that they
00:56:08build?
00:56:09Oh, the Diablo.
00:56:10Yep.
00:56:10Yeah.
00:56:11Diablo had 11 degrees of overlap, which is practically nothing.
00:56:19Whereas between the wars in the 1930s, there were motors running overlap 80, even a hundred
00:56:29degrees.
00:56:31So that's a bunch.
00:56:34Reminded me again of Kenny Augustine.
00:56:35His observation on cams was it's always important to remember that the only time an engine makes
00:56:42power is when the valves are closed.
00:56:46So yes, it's not a bad thing, not a bad thing to keep in mind.
00:56:51What people are, what's happening today is that, that, uh, the European union, uh, the EPA
00:56:58and the U S and competent, um, responsible organizations acting for other governments are saying,
00:57:05overlap, um, our new standard is going to require you to reduce that even further.
00:57:12So if you don't get this boost one way, try to get it in another way, less timing, greater
00:57:22valve lift.
00:57:23And this is why you're seeing now engines that don't turn astronomical revs being given formula
00:57:30one MotoGP style finger followers, because finger followers are light.
00:57:39The latest finger followers for that BMW that Mark was talking about now weigh eight grams.
00:57:48The reason that they are having to lighten the valve train so much is that to get the valve
00:57:57open a lot in a shorter distance means wham, you have to hit it hard to get it up to a speed
00:58:04that gets it over the nose of the cam and onto the closing side.
00:58:10So that acceleration, uh, would normally call for frightening valve springs made out of wire
00:58:20as thick as your little finger, but that's not going to last because oil complains when
00:58:27it's asked to carry enormous loads.
00:58:31It invites the two surfaces that are crushing it.
00:58:34Why don't you kill each other rather than me?
00:58:36And they do.
00:58:38Oh, there's nothing worse than that flat spot on the top of your cam that's been all scorched
00:58:43away.
00:58:44Yep.
00:58:45So, uh, and that's why in early times, race engines were constantly revved during warmup.
00:58:53In, in, in, because they're hoping that their oil film will remain complete and unpierced.
00:59:04Yeah.
00:59:05You want to keep that wedge, you roll, roll it down to a low RPM and you can squish all
00:59:10the oil out.
00:59:11Yes.
00:59:11And it's tragedy.
00:59:14Because those two surfaces love one another.
00:59:18Well, think of accelerating, you know, your bicycle, just standing next to it.
00:59:23You're going to push your bicycle down the road and it's one of those fancy ones.
00:59:27You know, it's one of those, uh, carbon fiber jobs.
00:59:29It weighs 15 pounds with tires and everything.
00:59:33Yep.
00:59:33And you can just run, you just start running.
00:59:36That bicycle is pretty much going to go with you, but to try to do that with your gold wing,
00:59:39you can't do it.
00:59:40That's like, that's what you're doing with your valve.
00:59:43Yes.
00:59:44Absolutely.
00:59:44You know, you're trying to accelerate this valve in a short period of time and that's
00:59:48where the, so much of the, you know, the real disco is going on is in, in the opening
00:59:53and closing ramps so that closing and that it doesn't close so abruptly.
00:59:58You're trying to bring the valve down ultra rapidly.
01:00:00And then at the very last second, you're kind of going, ah, and you're just setting it on
01:00:06the seat rather than letting you.
01:00:07Because you don't want it to bounce.
01:00:09Yeah.
01:00:09If it bounces, man, it's over.
01:00:11Yeah.
01:00:11And when I was at S and S, uh, the operator of the sort of emissions operation there said,
01:00:23uh, we have a Spintron here, which we use for, uh, evaluation of valve motion.
01:00:31And in NASCAR, he said, they're looking to limit valve bounce to three bounces after closure.
01:00:42It used to be five.
01:00:46And here, here is an example of how far regulation has changed valve timing.
01:00:56The, uh, V4 Panigale, Hatsi Tatsi, uh, street bike with all that horsepower has 26 degrees
01:01:09of valve overlap.
01:01:11Not a lot in traditional terms.
01:01:16Where, how do they make their power then?
01:01:18They make it in the manner that Formula One and MotoGP have determined to work.
01:01:28They've developed it to the point that it can be made reliable.
01:01:32Ultralight moving parts, high, high accelerations, and, uh, short timing.
01:01:41So, um, that is the response of the industry to being told to do away with, uh, overlap, valve
01:01:54overlap.
01:01:56And each time a tougher standard comes along, uh, the engineers have to scurry around and
01:02:04identify every detail, crevice volume, identify every possible source of, of emissions and
01:02:12struggle to meet the new standard.
01:02:17It occurred to me when you were talking about valve bounce that, um, good valves want to bounce
01:02:23like a good fitting valve.
01:02:24Like it's one way to check in a cylinder head without springs or anything.
01:02:29If you're lapping valves and that you want to, you know, know that the guide is, is just so
01:02:33cool and concentric with the seat.
01:02:35And all of that is really good as you can drop the valve and it'll go.
01:02:39Yeah.
01:02:40And if it doesn't bounce, it's not a good fit.
01:02:42It means that, that something's off center.
01:02:44Yes.
01:02:44Yeah.
01:02:45Um, that's a good point.
01:02:48Intake valves used to have this flaring shape that came from Brooklyn's speedway.
01:02:56What they found was with early valve materials, exhaust valves naturally gave them
01:03:03themselves that shape.
01:03:04The spring is pulling the head of the valve is red hot and it sort of says, well, okay,
01:03:13you, you'll go that way.
01:03:15I'll go this way.
01:03:16And so people gave valves that tulip shape and reckoned that it must be good.
01:03:23Well, it turns out, and this is another case of multiple inventions, at least four of what
01:03:31Ford called the nail head valve.
01:03:34They made quite a big deal of it back in the sixties when they discovered that a valve whose
01:03:41stem just went down and attached to it pretty close to a flat disc, flowed a lot of air.
01:03:48So, uh, tulip valves on the intake side?
01:03:55No.
01:03:56Again, uh, referring to, uh, Augustine, Kenny Augustine, um, very different case from intake
01:04:08to exhaust.
01:04:09The exhaust side, the tulip shape can work.
01:04:13On the intake side, no.
01:04:19So I have in a window in this office, a number of valves from different kinds of engines just
01:04:27to invite me to look at them and maybe have an idea or discover a connection.
01:04:36I like to have these things around talking to me.
01:04:39I have a lot of failed parts for that, so.
01:04:44Yes.
01:04:45It's really charming.
01:04:46Lots of us have those, uh, collections of all my smeared, yeah, my smeared pistons and
01:04:53the, you know, it's, everyone's getting thirsty, but the Vela set when I redid, I got rid of the
01:04:59hairpin springs and these redid the guides and, uh, it was a three inch, a three inch stem on the
01:05:06exhaust and now you can buy all this stuff that's just unassailably awesome materials and you can
01:05:11have a five sixteenths.
01:05:13You can have a tiny little, tiny little stem and it'll hold up just fine.
01:05:23How do we, how far we've come from exhaust pipes?
01:05:27Indeed.
01:05:28Well, it's all, you know, it's all part of the symphony that we're looking for and we
01:05:33go, you know, I was going to bring up, uh, exhaust or a cylinder pressure, you know, you
01:05:37have 120, say 170 PSI when you crank it and you check your compression and then you, you
01:05:44know, pulls in the mixture and it's coming back up and it's compressing this stuff and
01:05:48then you light it off and it's usually what?
01:05:5010 to one, whatever your compression ratio is, you're going to go up.
01:05:53A hundred times the compression ratio is the rule of, yeah.
01:05:58Yeah.
01:06:00I'm tired of rules of thumb, Kevin.
01:06:01You know what?
01:06:02Because I've been reading all of these things about, oh, the, um, here's a rule of, here's
01:06:10a formula for the rule of thumb on the diameter of the primary that you should make the header
01:06:14for your, your Ford V8 and I go and I do my math and on the Ford 460, it says it should
01:06:21be, I did the math and I did it right at 2.1 inches.
01:06:24I'm like, this is a 4,500 RPM engine.
01:06:28That seems, it doesn't seem right.
01:06:31And then you go into the market and it's a very rare engine that has a two inch primary.
01:06:36I have a friend racing a V8 Mustang with a 358 and it has a stepped header.
01:06:42So the initial pipe is an inch and seven eighths and that thing revs to 9,200 and is making
01:06:50800 horsepower, inch and seven eighths.
01:06:52And then some distance is the next step and it gets a little bit bigger.
01:06:57And I think it's got three steps before it gets to the collector.
01:07:02And what's going on there?
01:07:05What's fascinating to me is that I'm sure that big, big exhaust companies have lots of
01:07:11pressure transducers.
01:07:13They're able to measure.
01:07:14They have.
01:07:14And they're, they're sticking this stuff everywhere and measuring all this stuff and trying to
01:07:19make sense of it.
01:07:20And then you have the chart, you know, for me, I'm still trying to get a grip on
01:07:24the crank throws and when the pressure wave is happening and how it relates to the other
01:07:31cylinders and then where's the collector, the temperature of the gas varies the speed
01:07:39of the wave.
01:07:41It does.
01:07:42And so here's another variable.
01:07:45And, and I, a lot of times I think like in the car industry, B8 headers, inch and three
01:07:52quarter primaries, incredibly common.
01:07:55Lots of people have done lots of dyno testing and this is what we end up with, but it's just,
01:08:02it's just like, get, grab some of that tube and let's try this.
01:08:06That's how it is.
01:08:07And let's try this and like make this long.
01:08:09And like those pipes, like you would see pipes at Brooklands that were like three feet
01:08:14beyond the rear wheel.
01:08:15Yes.
01:08:16And they were trying to, just huge, like struts holding this pipe, like so far behind the
01:08:22vehicle.
01:08:23It's just, it's really crazy.
01:08:25It's working.
01:08:26Yeah.
01:08:26Well, um, those, uh, people building hot Bonneville, Triumph Bonnevilles in the 1960s, they,
01:08:39like the look of big head pipes, big chrome head pipes that turned blue from heat.
01:08:48Now there is a dynamite combo.
01:08:52Just can't be beat.
01:08:53Then Triumph 500s win the Daytona 500 with little dinky, little tiny head pipes.
01:09:03Well, all right, let's try that.
01:09:07Oh, it works.
01:09:09Um, well, at a distance of two or three weeks, now I'm looking back on that and starting to
01:09:19look beautiful.
01:09:21This is what happens when something wins races.
01:09:24Yeah.
01:09:25Becomes attractive.
01:09:26Everybody wants it.
01:09:27So, uh, if you want to do the scientific method and have repeatable and reliable results, you
01:09:38have to have some self-discipline.
01:09:40It's great to have enthusiasm because if you didn't, you wouldn't be there.
01:09:45You wouldn't own a motorcycle.
01:09:47You wouldn't have spent all that money on stuff to help you understand.
01:09:53So, um, yes, we need that enthusiasm, but if we let it get away from us, we'll put big header pipes,
01:10:04oversized headers on our, on our Triumph 650.
01:10:07So it's good to keep close to the data.
01:10:13It is as much as you can, but that's, what's so fascinating about the exhaust pipe is the,
01:10:18even with all the sensors, we still really don't have all the data.
01:10:23No, people don't know exactly how it works.
01:10:27And there's, there's just dyno people out there who are like, well, let's build this thing.
01:10:33And we'll, we'll use a two inch secondary.
01:10:38We'll use a two inch, you know, three inch collector or two inch collector.
01:10:42Well, let's make the collector long.
01:10:44Let's make the collector high volume.
01:10:46Let's, you know, all these, and they're just trying stuff and there's, and what's working
01:10:51against what, you know, you change one thing upstream and then you move your collector
01:10:55and suddenly nothing works or it works amazing, but you don't know why.
01:11:02Here's one that happened to me.
01:11:05Uh, somebody said, would you make me a set of pipes for my 250 for Daytona?
01:11:13And I thought, what do I know?
01:11:15Well, I keep a big file of every exhaust pipe that I've come across with measurements.
01:11:23So I was able to look at what Yamaha had been doing year by year.
01:11:28And when I did that, I saw that as they made the head pipe shorter, they made the taper greater.
01:11:36Well, let's, let's get out the formula for the volume of a truncated cone.
01:11:43Well, this is why we graduate to get away from stuff like this, but I needed it.
01:11:49Didn't I?
01:11:50When I, when I ran the numbers, I found that the volume of the head pipe was remaining constant
01:11:56as they shortened it and tapered it more.
01:11:59So I thought, hmm, that's interesting.
01:12:04I wonder what it means.
01:12:07Yeah.
01:12:07And what it probably means is when that, the volume in the cylinder has expanded that much,
01:12:17it's time to start the, the first divergent cone.
01:12:23But at the same time, it can be, it can be simple.
01:12:29Things like people say, well, take 20 millimeters out of the header pipe, take 25 off the head
01:12:38and raise the exhaust a millimeter and widen them a millimeter on each side.
01:12:47And there's a big improvement, but it may not be the optimum improvement.
01:12:52That's why the dyno is there.
01:12:54It's great to have this enthusiasm to say, let's saw things up.
01:13:00Let's weld them together in a different way.
01:13:03The goal is to learn something and to understand so that when you're having a bad day, you may know
01:13:11what to try first.
01:13:13It might work because you've gained understanding.
01:13:17At one point, Ducati was making header pipes on, they're making those great big V-twins and
01:13:24the header pipes were humongously large, just monster.
01:13:29And I'm looking at this and I'm thinking, those are bigger than the header pipes on a 4360.
01:13:37A 28-cylinder radial aircraft engine.
01:13:40Yes.
01:13:41Displacement of 4,360 cubic inches.
01:13:44So I thought, okay, let's see what the timing looks like and the RPM and so forth.
01:13:54And it all made sense, given that this volume of gas had to get through this hole in this
01:14:03length of time.
01:14:04And in the Ducati, it had to get through, it was a smaller volume, but it had to get
01:14:09through a much shorter time because the Ducati was turning, what, 11,000, 12,000.
01:14:16And the 4360 was turning 2,700.
01:14:20And it all worked out that, yeah, those pipes are fairly, it's a good comparison.
01:14:34It made sense.
01:14:35So it's, what we want is results.
01:14:47And empiricism gives them very quickly, just try a lot of stuff on the dyno.
01:14:54The chemists call it combinatorial analysis, which means try everything on the shelf.
01:15:00Now, what's this white powder?
01:15:02Let's try some.
01:15:04Let's dignify it with a long name, combinatorial analysis.
01:15:09But the theoreticians are working off somewhere else.
01:15:14Used to be Dr. Blair.
01:15:15There's a bunch of others.
01:15:18And they're trying to predict all of this.
01:15:20They're trying to develop math models for it.
01:15:24Well, it could be that Ducati has something really good, but they're not publishing it.
01:15:31The NASCAR people aren't publishing theirs because they have a use for it.
01:15:38When it's old hat, like those Honda Formula One reports, they publish it.
01:15:46And we read it and weep.
01:15:49Oh, to be able to have the facilities and the backing to do this kind of work.
01:15:57But we don't.
01:15:59So what's for lunch?
01:16:01Yeah.
01:16:01Gosh.
01:16:07So many variables.
01:16:09Yeah.
01:16:09Again, it's why it's fascinating.
01:16:11And you constantly seek to kind of get a grip.
01:16:15There are two ways to get a solution.
01:16:17There's a math method.
01:16:19And there's, instead of using silicon logic, we use the logic of steel and titanium.
01:16:27Because reality is going to do the calculations its own way.
01:16:33We just don't understand it perfectly.
01:16:37Wonderful.
01:16:38Yeah, it is.
01:16:39Well, it's like the tire guy who said, I just look at the tire.
01:16:47Yeah.
01:16:48And you think, oh, okay.
01:16:50But if he sees a wear pattern in the tire, he knows what that means to suspension damping.
01:16:57There's nothing theoretical.
01:16:59It's like, no, you need more rebound damping.
01:17:03I mean, that's why that's doing that on your tire, you know?
01:17:07And then there's a good wear pattern where you think, yeah, this is pretty solid.
01:17:11And electronics can't fix it.
01:17:14You know, it's like a lot of these guys talk about when they do their testing, they work
01:17:18on mechanical grip first without all the hoo-ha.
01:17:21Yeah.
01:17:22It's not just making the bike work and then adding your other elements to it later.
01:17:29Anyway, that ain't a tailpipe.
01:17:33Oh.
01:17:35There are formulas for roughly perfect smokestacks out there.
01:17:39You can start with math.
01:17:40You can start, you know, get your TIG welder fired up and go get one.
01:17:45Get your saw.
01:17:46Make your joints nice.
01:17:47Don't make them bumpy on the inside.
01:17:49Purge your system before you weld it.
01:17:55We'll talk about that later.
01:17:56But anyway, thanks for listening.
01:17:57That's the Psycho World Podcast.
01:18:00The mystery of exhaust pipes goes on.
01:18:05And hit us down in the comments.
01:18:07Tell us what to talk about.
01:18:08Give us some topics you want to hear about.
01:18:10We'd love to...
01:18:12Learn about them.
01:18:14Learn about them.
01:18:15Yeah, we'll start.
01:18:16Thanks for listening, folks.
01:18:17We'll catch you next time.
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