We're taking a flyer on this one but we couldn't resist talking about AIR! True to form, Technical Editor Kevin Cameron starts talking about us breathing and how gravity holds air on the earth ("Which is really good for us.") and we take it from there. Poppet valves, pressure waves, exhaust and intake tuning, and so much more. Ever heard of an Aspin valve? Rotary valve? Sleeve valve? You can say yes to all those if you just have a listen to this week's Cycle World podcast. Join us in the air!
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00:00Welcome to the CycleWorld Podcast. I'm Mark Hoyer, Editor-in-Chief. I'm with Kevin Cameron, our Technical Editor.
00:06This week we're going to talk about air. Air. All that we take for granted. The qualities of air.
00:13That would be a, it is a broad topic, but we're going to kind of concentrate on the management of air, really going into the engine.
00:22The qualities of air and some things about air that we don't immediately think of.
00:29And what do you think of all that, Kevin?
00:33Well, I think, first of all, here we are breathing 17 times a minute to take in the atmosphere for its oxygen.
00:45Because like an internal combustion engine, our bodily economy depends upon oxidizing our fuel with oxygen.
00:57And that gives us vitality.
01:01I must need to breathe more. I need some more vitality.
01:08The air that we breathe is held on the earth by the earth's gravity, which is really good for us.
01:17And it's roughly 78% nitrogen, which for most purposes is inert.
01:25It does combine to a very minor degree with oxygen at very high temperature.
01:31Ooh, nitric oxides.
01:33Nitric oxides, yes, sir.
01:35Better keep that out of the tailpipe if we can.
01:38And when all those nuclear scientists were waiting for the Trinity test, the first atomic bomb, there were some people who were a little nervous.
01:48Because what if the intense heat of the bomb ignited the atmosphere?
01:55Fortunately for us, it didn't.
01:57So nitrogen kind of keeps to itself, so we don't have to consider it.
02:04And then trace elements are carbon dioxide.
02:07Everyone's worrying because there's 417 parts per million now, but it's essential for plant life.
02:15So what we're interested in, the engine business, is the roughly 20% of the atmosphere that is oxygen.
02:23And although we have all these expressions like give it the gas or gas it up, when you operate the throttle, you are controlling only airflow.
02:37Either the butterflies of fuel injection throttle bodies or the slide of a carburetor, you're controlling the air.
02:51And the carburetor or the computer-controlled digital fuel injection adds to that mass of air the right amount to combine with all of the oxygen, leaving no unburned fuel, no unreacted oxygen.
03:09And that state is called correct combustion and occurs at about a weight ratio of 14.7 parts air to one part of fuel.
03:19And that can readily be ignited by a spark.
03:25But mixtures that have 20% more fuel or 20% less fuel than that ratio, the engine starts to misfire and it may quit altogether because the spark can't ignite those far out mixtures.
03:42So the old idea that some people have that, well, the more fuel you can push through the engine, the more power you'll make, it's not true.
03:50What we're trying to push through the engine is air because if we can fill the cylinder and it is being done by very well-designed engines to 125% of full, we can make a lot of power.
04:08And so one of the measures of how well-designed an engine is, is how well it fills its cylinders.
04:20As cylinder filling goes up, torque rises with it.
04:27As cylinder filling becomes poorer, torque falls with it because the degree of cylinder filling determines how much mixture of fuel and air we can burn in that cycle.
04:43And so we're all looking to fill our engines as well as possible.
04:50The measure of how well the cylinders are filled is called volumetric efficiency or VE.
04:59And you probably at least vaguely remember reading about volumetric efficiency in somebody's article somewhere.
05:06But 100% means that you filled the cylinder to its displacement.
05:12You do your high school geometry and you find the area of the bore, pi R squared, R being the radius of the bore, times the stroke length.
05:24And that gives you the volume.
05:27So this is why a larger engine takes in more oxygen.
05:34Therefore, it can make more fuel.
05:36Or an engine that is supercharged, that has a pump to force air into the cylinder, can make more power.
05:45And also an engine that revs very high, that is filling the cylinder many more times per second, also makes more power.
05:56So anything that allows us to burn a larger mass of fuel-air mixture is going to make more power, other things being equal.
06:06I mean, if we've got a completely incompetent design, it's not going to do well anyway.
06:12But these are the basics.
06:17And when you turn the throttle towards closed, the piston pulls a partial vacuum.
06:25And at idle, it may be 25, 26 inches of mercury.
06:31That's why we call it a throttle.
06:33Yes, because it...
06:35It's going to throttle you, right?
06:36Yes.
06:37The engine wants to run until it explodes.
06:39The engine's preference would really just let me go.
06:42Yes.
06:43And that's why we hold it back.
06:45Because we have respect for our connecting rods and piston cracking and all those tiresome subjects.
06:51Go ahead.
06:54Well, I was going to ask what...
06:56You know, forced induction supercharger, turbocharger is essentially increasing the displacement.
07:03It is.
07:04It's pushing a bigger engine's air through a smaller engine.
07:08Yes.
07:09But what allows us...
07:11Well, what are the qualities of air that allow us to fill a cylinder to 125% without stuffing it in using a pump?
07:22Well, air has mass, which is why the earth is able to attract and hold it, so we can breathe it.
07:31And that mass...
07:33Well, here's an example.
07:37I visited General Motors at one point.
07:40And I saw a little piece of data sheet on the window of one of the dyno rooms.
07:49And they had dynoed a 400 Yamaha.
07:53And what they were doing is measuring the pressure inside the cylinder with a little microphone.
08:01And this high RPM engine, fairly high RPM...
08:08Basically, the air in the intake pipe was not moving during the first half of the piston stroke.
08:15The reason being that the air has mass and it therefore has inertia.
08:21If we're all standing around in the room and somebody yells fire, it's going to take us a while to accelerate toward the exit.
08:30And what happens is that the piston pulls a partial vacuum for about half of the stroke in a high RPM case.
08:40And the air is starting to move.
08:44And then in the second half of the piston's downstroke, intake stroke, the air accelerates until it's moving at several hundred feet per second.
08:54And it's just roaring in there.
08:59And this is why when the piston reaches bottom center at the end of the intake or suction stroke,
09:06we leave the intake valve or valves open for some time after bottom dead center.
09:13Because we've got a fortune in kinetic energy, air rushing.
09:18Leave the door open, a lot of molecules are going to rush in.
09:23And as the piston starts to rise, it starts to raise the pressure inside the cylinder.
09:29That pressure is opposed by the inertia of the inrushing air.
09:34And at some point, it's advisable to close the intake valves and trap all that lovely stuff in there.
09:41Well, it's one of those great observations.
09:45Who was that, the flow bench guy?
09:48The engine only makes power when the valves are closed.
09:51It's important to remember the engine only makes power when the valves are closed.
09:55The late Kenny Augustine.
09:57Kenny Augustine, yeah.
09:58Who was a wonderfully bright guy who spent his life with airflow and then got interested in constitutional law rather late.
10:11So there is a science to this valve timing business.
10:21I've just explained why we leave the intake valves open for a time after bottom dead center.
10:27Because once the air is accelerated, rushing into the cylinder,
10:31it makes sense to let it rush in until no more can rush in just as the valve is closing.
10:38So let's talk about, well, do you have something you want to finish?
10:42Well, I wanted to say that there is no valve timing that is ideal for all speeds.
10:48So for example, if we had an old style Harley-Davidson two valve engine,
10:56they leave the intake valve open for not very long after bottom center.
11:02And the reason for that is that one of the most valued things in a large touring motorcycle
11:09is the ability to heave that 800 pound lump into motion.
11:15And that means these people aren't going to want to slip the clutch at 7,000 RPM to get going.
11:22They want the thing to start going right away.
11:25So this is why touring engines have big bottom end torque.
11:31And they don't leave the valve open very long after bottom center intake valves
11:37because they don't want the rising piston to push it back out.
11:41Because at lower speed, lower RPM, the intake velocity is less because the piston is moving more slowly.
11:50And it can't crowd into the cylinder the way it can when it's moving at, say, 500 feet a second.
11:59So if we're going to go for a record at Bonneville,
12:04we want to leave the intake valves open as long as there's airflow on top end.
12:10And we may have some really ridiculous cam timing cards.
12:15Collect them. Trade them with your friends.
12:17Well, I had an MG Magnet with a 1500 inline-4.
12:21You know, it's a British saloon sedan, 1958.
12:26And the intake valves, the valve timing was opening at top dead center.
12:31Yes.
12:33And it surely did idle beautifully.
12:36It would. And the EPA would strongly approve of it.
12:40Because if the valves are not...
12:45There's a situation that can occur at top center at the end of the exhaust stroke, which is called overlap.
12:51The intake valves are already opening before top dead center because we want them open sooner in the suction stroke.
12:58And the exhaust valves, we want the exhaust process to be as complete as possible.
13:05So we don't close the exhaust valves until some distance after top dead center.
13:10So the two valves are open for a little while together.
13:14And that means fresh charge from the inlet can sail out the exhaust.
13:19And the EPA is right there.
13:22And they say, unburned hydrocarbons, you will have to pay a large fine.
13:27Indeed.
13:28To the manufacturer.
13:30So, onward.
13:33Well, I would like to talk about the suction signal, the intake.
13:39So, the piston starts to go down in the cylinder.
13:43The intake valves are open.
13:45The creation of vacuum, negative pressure, is occurring in the cylinder, really.
13:54It's happening at the top of the piston.
13:56Yes.
13:57So that's where the inertia is beginning.
14:01That's where the signal of negativity is then creating a wave, correct?
14:07Which travels at the speed of sound, local speed of sound, up the intake.
14:12So it takes a while for it to spread the message, like Paul Revere, all the way along the intake pipe.
14:22So that the molecules there start to, we're wanted over here.
14:28Come on, guys.
14:30And they start to rush in.
14:34And at low RPM, it's a fairly simple process.
14:41Kind of like pumping up a bicycle tire with a manual pump.
14:45But at higher and higher speeds, as Rob Muzzy once said, the harder you tune on a four-stroke, the more it begins to act like a two-stroke.
14:57Tune on a four-stroke, it begins to act like a four-stroke.
15:00A two-stroke.
15:01You get the idea, I hope.
15:03Anyway, the thing is that four-stroke engines have a great appeal for their utility in society.
15:12Because they are more like linear devices than any other combustion engine.
15:18But if you begin to increase the overlap and rely on exhaust pipe waves and intake waves and all these inertial effects, which are what make two-strokes powerful, then a four-stroke begins to act more like a two-stroke.
15:37It has a narrow power band and it has a strange dependency on intake and exhaust lengths.
15:47Which is true of four-strokes, where we're utilizing those pulses quite a bit.
15:53Even in street bikes with airboxes and varying lengths of intake trumpets inside the airbox.
16:02There's the fabled Helmholtz resonator that was popular for Buells to kind of stuff it in in the mid-range and keep it quiet at the same time.
16:15Can you give us kind of a tour of...
16:18I mean, you're making the wave and it's traveling sonically.
16:23Upstream.
16:24Upstream.
16:26And so it's sending the signal into an airbox.
16:30The tube is a certain length.
16:33And we're waiting for the wave to come back, yes?
16:36Sure.
16:38So much of this material was discovered early in the 20th century by practical people.
16:46For example, working at the Great Brooklyn Speedway in England, which was built 1907 or thereabouts.
16:55And they found that intake length made a difference.
17:01And, of course, what's going on is the piston produces a suction pulse.
17:06It travels up the intake pipe, is reflected at the open end as an opposite wave, a positive wave.
17:16And it may bounce back and forth several times while the whole engine cycle is going on.
17:21But what we want is for a positive wave to arrive at the intake valve just as it's opening.
17:30And in that way, you can gain maybe 10 or even more percent of torque over a certain RPM range.
17:45At other ranges, the sound waves either don't help you or they may work against you.
17:51Which is why if we have a lot of overlap, which means those two valves, the valves are open together for a longer period of time.
18:02There is a longer period for exhaust waves to reach the cylinder and affect the intake.
18:11Which works as follows.
18:15We have the engine fires, power stroke takes place.
18:21As the piston nears bottom center, the exhaust valves begin to open and they release a high velocity exhaust outflow into the pipe.
18:33And that thing rushes down to the end of the pipe and is reflected as a negative wave.
18:39When you go to the end, an opening at the end of a pipe, it reverses the signal.
18:48So the positive wave comes back towards the engine.
18:53Negative wave comes back towards the engine.
18:57And it can propagate into the cylinder through the exhaust port.
19:06And then into the intake through the opening intake valves.
19:11And it can play come hither with the intake flow, even though the piston is essentially stopped at top dead center.
19:21The piston is not pumping. It's waiting there, slowly reversing its direction.
19:27So we've created a wave in the exhaust.
19:30We've made the exhaust a certain length so that at the RPM we're interested in.
19:35This negative wave comes back and causes intake flow to begin to enter the cylinder.
19:41This is desirable because at top dead center, at the end of the exhaust stroke, there is a volume above the piston.
19:50That's the combustion chamber itself.
19:52That's filled with exhaust gas.
19:55That's going to dilute the next intake charge if we don't blow it away.
20:00And that negative wave from the exhaust aspirates that nasty exhaust gas into the pipe and begins the intake process.
20:11So basically the combination of the exhaust length and the valve overlap gives the intake process a head start.
20:24So that's another way in which the length of an input-output device affects torque.
20:39And so we're manipulating that now on street bikes.
20:42We're manipulating the volume. There's sometimes multiple volume airboxes that help fill in.
20:50If you get your resonance at peak power is 10,000 and you're really ripping at 10,000, you're going to have the fabled dip in the torque curve.
21:02And they're filling that in by getting multiple resonance out of intake and exhaust systems.
21:10And so we get the best of both worlds.
21:13Plus we can now add variable valve timing and we can get that overlap.
21:19You can either have the timing like this, this being the overlap here.
21:24This is Kevin crossing his fingers again for you on Spotify.
21:28He's overlapping the valves and he's showing them open at the same time.
21:32Yep.
21:34But that is what variable valve timing does.
21:37And if you open the hood on a lot of modern cars and look at the cam covers, you'll see these big lumps on the drive in.
21:46And that's where the cam phasers are located.
21:48And some of them are hydraulic and some of them are, I think some of them are electric even.
21:54But their job is to change cam phase according to a schedule that has been determined on a dynamometer.
22:04Say, okay, well, that's good.
22:07Hold that.
22:08Write that one down.
22:09Yeah.
22:10Now, even without VVT on motorcycles, I've looked at thousands of dyno charts over the years.
22:17Sure.
22:18And in this discussion, I want to give a shout out to Honda because Honda torque curves and power curves in general are very refined.
22:33I mean, from like 250, 300cc dual sport bikes to 1000cc sport bikes, they really have done consistently a very good job of refining the torque curve.
22:47It's pretty artful.
22:48I've seen it with other manufacturers.
22:51It doesn't have horrible dips in it.
22:53No dips.
22:54We set our smoothing and we have our SAE correction factors and all that stuff.
22:58But in general, hundreds of motorcycles, more than a thousand.
23:04I mean, I can't even imagine how many dyno sheets I've looked at because we've been running the dyno at Cycleworld since sort of mid-90s.
23:15And we have all those charts.
23:17But it's really something and it takes a lot of effort to make that happen.
23:23Well, Dynojet came out with their low-cost dynamometer that came with software that enabled a shop owner or an individual investigator to do fairly sophisticated dyno work at an affordable cost.
23:45And they sold thousands of those dynos.
23:48And one of the first things that happened when the dynos went on the market was Mark Dobeck began to get these nasty phone calls.
23:57And people are saying, your goddamn dyno is giving me a flat spot and I can't tune my way out of it.
24:07And what's happening there is that at some RPM, other than the one at which the pipe length is correct, some lower RPM, instead of a negative wave coming back to the cylinder and starting the intake process early, it's a positive wave.
24:29And it blows exhaust gas into the cylinder and out the intake valves and fills the intake port and even blows back into the airbox.
24:40So that when the piston finally says, okay, I'm going to do it now, and it starts down on the suction stroke, the first 30% of the cylinder fills with exhaust gas.
24:52So naturally, you've got this lovely power peak up here from the correct length of the exhaust pipe at that RPM, and then it drops into this deep hole.
25:03And the wider you make the overlap timing, the deeper the hole and the taller the peak.
25:14And as a result, the curve that joins the two from way down there to way up here is so steep that no one can ride that motorcycle off a corner at anywhere near the traction limit.
25:29So racers were really upset about that flat spot and people would tune and tune and tune.
25:38They said, yeah, we leaned it way out and it seemed to help, but it killed the power everywhere else.
25:45Well, no surprise, because what's happening is first exhaust gas blowing out the intake valve goes through the carburetor backwards.
25:59It picks up fuel. Carburetor doesn't care which way the air is going.
26:03And then it sucks it back in and picks up fuel the second time.
26:08So it's double rich and it won't run. It stutters. It misfires. It gobbles.
26:15Yeah. I mean, the first time I ever saw a standoff, when I saw a mixture, a cloud.
26:23Oh, yeah.
26:24A cloud of fuel on the outside of the carburetor intake.
26:29Anybody got a lighter?
26:31I was just blown away that that could happen.
26:34And I always struggled with envisioning this stuff without it sort of being instantaneous.
26:43And it's none of it is instantaneous. We cannot instantly open a poppet valve.
26:48It takes time. It takes time.
26:51It takes time for the signal to run from the dome up to the intake to get the to make suction happen.
26:58Like it's got to travel down the pipe.
27:01And it's I think the magic of tuning is someone who's able to kind of visualize those timings and manipulate them and learn to.
27:14They become familiar through experience with the kind of thing.
27:18Oh, this reminds me of something that happened at this point.
27:22Or this is the way a lot of people talk about it, because these learning experiences are intense.
27:29When you begin to pick out a simple tune on the keyboard, it's a thrill.
27:35And the first time that I was able to make a fast 252 stroke, I just felt a tremendous elation that made me cheerful the whole rest of the day.
27:48And so the practitioners of these dark arts remember these learning experiences very fondly.
27:58And nothing is remembered like stuff you've taught yourself.
28:04Now, some of these people are quite unsophisticated in terms of engineering or physical science, but they know what they're doing.
28:15They can get results because they have the experience to be able to say, hmm, this is looking pretty mysterious, but let's try this.
28:24Oh, that's a little bit better.
28:26Well, now we're on our way, aren't we?
28:29And so I think that that kind of experiential knowledge is admirable.
28:40So you can, of course, lose yourself in all the variables.
28:49Well, the cam timing, the compression ratio, the amount of overlap, the intake and exhaust lengths, but people just get through it.
29:02And sometimes, here's another one of those old saws.
29:07They say, never change more than one thing at a time, because that way you know what's causing the change.
29:16Well, that makes sense.
29:18Let's do it that way.
29:20One wealthy California race sponsor said to his man, I want you to buy 40 TZ250 cylinders, and we'll have them modified each in a different way, and then we'll test them.
29:34And then we'll know.
29:36They were all worse than stock.
29:38All of them worse than stock.
29:41So I thought, who am I to go against this wonderful truth?
29:54But what I found was that if I raise the exhaust port one millimeter and widen it a millimeter on either side, raise the compression by milling 25 thousandths off the head and recutting the water seal groove, and shortening the exhaust pipe header 20 millimeters, I had a really fast bike.
30:22Who knew it was a system?
30:24Yes, it's a system.
30:26So when you raise the compression, you lower the exhaust temperature, because raising the compression takes more energy out to drive the piston, leaving less to go out into the exhaust pipe.
30:44So colder gas is going into the exhaust pipe, so now the engine, it's running, it's lost 500 or 750 revs.
30:54Well, we want those revs back, so now we shorten the exhaust pipe.
30:59And if the engine is going to run at a higher speed, it needs more exhaust area exposed just before the piston begins to open the transfer ports to let fresh mixture into the cylinder.
31:14So it is a system, but people get a feel for it.
31:20And I think Rob Muzzy is a favorite example because he found out from running and running and running on the dyno, he said, don't imagine that you're going to learn something on the dyno and then generalize it to your race bike, which is over there in the truck somewhere.
31:40He said, test what you race, because so often you think you've done something, but what you've actually done is a little different from what you think.
31:52So this makes skeptics out of people.
31:58And there are so many sectarian views of how to use a dynamometer.
32:04Oh, no, you have to step test, hold it at a constant RPM for so many seconds to stabilize.
32:11Well, that's going to wear my engine out.
32:14I can't afford that.
32:16And those people, those step test people just didn't like the new Dynojet dynos, which just go brrrrp, and that's a test.
32:26Yeah.
32:27You've run across this RPM range, you've got a torque for each RPM, it's all in the computer.
32:33Yes.
32:34What's not to like?
32:36I think we've seen learnings here of doing that at half throttle as well.
32:43Yeah.
32:44Because the behavior is different.
32:46Sure it is.
32:47And so as a general rule, we're testing, we're clicking into usually fourth gear because it's the closest to direct.
32:55And hitting it as wide open is at a low an RPM as it will take, which is pretty darn low with most of these fuel-injected engines that aren't relying on signal alone.
33:08Yes.
33:09That means the air is flowing and we're squirting in the fuel.
33:12We're not waiting for the air to draw the fuel through an orifice like in a carburetor.
33:17So you can just let her rip.
33:21So the Inertia Dyno, I mean, it's been fabulous.
33:26It's a great jetting tool too, what I found.
33:30You know, you can set up your lean, your mixtures at cruise.
33:36You can say like, oh, let's do 3,000 RPM in top gear and see what happens when the throttle's cracked just barely and see how it runs and then transition without being out on the road.
33:48And I think what we, and I'm not even relying on a chart to get this information.
33:54I'm just doing that so that I can concentrate on what's going on without running into the back of a Ford Explorer and watching Little Mermaid with a kid.
34:05You know, it's like we can do this in a controlled environment.
34:12But getting the dyno into a lot of people's hands gave us, you know, it was a kind of democracy in the sense that you could then find your flat spot and kind of tune for that area under the torque curve, which is really your successful acceleration.
34:32And then there came that fateful day at Daytona when four-into-one exhaust pipes on four-cylinder engines just disappeared.
34:42Not a one could I find in all the garages.
34:46And what had happened was somebody had decided not to put up with that flat spot any longer.
34:55And what they did was they joined the header pipes in pairs.
35:03So it became four into two, the joint, into one.
35:10And by having a second enlargement where the two individual pipes joined a larger pipe, that acts like a pipe end because it allows the gas to expand.
35:25And it expands in all directions when it's allowed to, including back up the pipe to the exhaust valve.
35:33So by putting a second enlargement in the middle of that four-into-one pipe, turning it into a four-two-one, they were putting a negative wave on top of the positive wave and canceling it out.
35:55So now the torque curve was no longer...
36:00And it became much more rideable and everybody went quicker.
36:05And we'll call it progress.
36:10In certain areas, humans haven't made a lot of progress, but there's one and let's cling to it.
36:17So now I want to talk about our adherence to the poppet valve.
36:28Every engine out there, Mazda flirted with the rotary, which had its own unique qualities.
36:39But the poppet valve is in every four-stroke pretty much.
36:43And almost invariably, it's overhead cam.
36:48We have a few deviants out there still with pushrods.
36:52But poppet valves, why do we like them so much?
36:56Because there have been rotary valves, cone valves, sleeve valves.
37:02There's all these disc valves.
37:04There's all these different ways of controlling.
37:05We could certainly get into two-strokes, but because four-strokes have basically won the battle.
37:13All the ways of controlling air getting into a four-stroke.
37:16We have our limitations with poppet valves, which will float and get thrown off their camshafts if you spin them too fast.
37:23And how stiff can we make the springs?
37:26Nope, too stiff.
37:27The cam's going away or whatever it is.
37:30But why not just make a...
37:32I know it's a podcast.
37:33We got to talk and there's people on Spotify are going to be like, what's a sleeve valve?
37:38But maybe help us visualize if you might.
37:42Well, the one thing that has kept the poppet valve where it is in all the engines of the world is that nothing is moving when it is closed.
37:55There's no rubbing.
37:57There's no sliding.
38:00It's like a manhole cover in the street with rush hour traffic rolling over it.
38:09It doesn't require a lot of fussy business.
38:13Now in those huge aircraft engines, the poppet valves were like two and a half, three inches in diameter.
38:23Tremendous, great big thing.
38:24So the exhaust valves got very hot because they're being heated on both sides, the side that faces a combustion chamber.
38:32And when the valve lifts and the exhaust gas rushes out, heats the back of the valve.
38:37So they decided to deal with that by half filling the hollow valve with liquid sodium.
38:44And that worked well.
38:49It helped.
38:51So the sodium's ricocheting around in its little chamber.
38:54And carrying the heat up the stem.
38:57Yes.
38:59Normally, most of the heat of the valve travels out of the valve through its sealing surface into the valve seat ring, which is a part of the cylinder head.
39:08Which is either water cooled or it's covered with fins.
39:12No wonder we wreck those things so much.
39:14Yeah.
39:15So the hot exhaust valve acted as an ignition source.
39:23Or it caused the engine to detonate, which is an abnormal form of combustion.
39:28In which little pockets of the very last part of the mixture to burn just go pop all by themselves.
39:35And burn at the speed of sound.
39:38And they make an awful slap when they hit the inside of the combustion chamber.
39:42We call it tinkle or knock or what have you.
39:45So one group of engine manufacturers decided to do without the poppet valve.
39:51And what they came up with was a sleeve valve.
39:58This is worth seeing on YouTube, folks.
40:01So it's a sleeve valve.
40:04On this end, there was a peg and a ball on it.
40:11And here was a crank going round and round that clenched that ball so that this thing made this motion.
40:26And these ports, some of them functioned as intake ports only, some as exhaust only, and some were shared.
40:34But the way this motion causes them to open, these make a very efficient kind of port.
40:43And the sleeve is constantly moving, which means that the oil film between it and the outer cylinder is maintained by the motion.
40:54And transmits heat quite well.
40:58So the sleeve did not overheat and burn up immediately.
41:01And many thousands of aircraft engines like using sleeve valves like this were built in Britain by Bristol and by Napier.
41:13And today they're a curiosity because we don't use exhaust valves that big anymore for any purpose.
41:23And usually we don't have to fill exhaust valves with sodium because the valves are small enough that their heat can be transmitted to the valve seat.
41:34But on the other hand, this is why we don't make exhaust valve seats as narrow as we do intake valve seats.
41:43On the intake valve, we're mostly interested in making the seat as smooth as possible to invite the air into the cylinder.
41:51Smoothness.
41:53But for the exhaust valve, the seat has to be wide enough for the heat in the valve to be transmitted to the valve seat ring and into the cylinder head.
42:05Now, I know we were moving on from poppet valves, but it brings up a point what you're describing also, that intake valves are larger than exhaust valves.
42:14And that would be basically due to the density of the charge, correct?
42:18And heat, the temperature.
42:22Originally, they made the exhaust valves larger.
42:25And then people tried it all different ways and they decided that it worked best with a larger intake valve.
42:33Well, all we have to fill the cylinder on intake in most engines is the atmospheric pressure of 14.7 pounds per square inch.
42:42Whereas at the bottom, nearing the bottom of the stroke, the exhaust residual gas as the exhaust valve opens is of the order of 100 PSI.
42:53So, with that much pressure, it doesn't take that much valve.
42:58It wants to get out.
43:00And in fact, our favorite wise guy, Jim Fueling, and I'm very sorry to bring up his name for those people who didn't get on with him.
43:09But we all agree that he was a very clever man and he sold Detroit on the idea of solving their cylinder head heat problems by making the exhaust valve and the exhaust port smaller.
43:27And it worked.
43:29Because there's all this pressure to push the exhaust out.
43:33And the smaller the port and the shorter you can make it in the cylinder head, the less exhaust heat enters the cylinder head where it has to be trucked away by the cooling system.
43:48So, it's a big gain to sort of make the exhaust system disappear.
43:55As short as possible, as small as power will permit.
44:00He made a lot of money that way.
44:03He had a collection of tanks.
44:06He did, yep. And he had engines in a can.
44:09He had great big 4360s and engines in cans at his shop.
44:16I rode the W3 and I went up there and interviewed him and we talked about little kernel shaped combustion chambers that he was making for two strokes.
44:23So, he was taking the chamber and basically making nearly the entire diameter squish.
44:30And then putting a tiny little rocket shaped outlet with a spark plug in a tiny little kernel in the middle of it.
44:39So, it just got smashed up in there and then blasted out of that little hole.
44:44And he was making some power.
44:46There were guys in European GP racing back in the two stroke era who were firing their two stroke ignitions at 10 degrees before top center.
44:59So, that was probably pretty rough.
45:04Steep pressure rise.
45:06Yeah, but back to sleeve valves and other types.
45:10Because there was a rotary valve, I think that was a Roland Cross.
45:14Yeah, the cross valve.
45:16The cross valve was a cylinder that rotated and the exhaust pipe was connected to one end and the carburetor to the other.
45:27And in the middle of this cylinder was a diagonal septum and there was a port in the head that was roughly rectangular.
45:37So, that as the cylinder rotated, it would expose intake as the piston descended on its intake stroke.
45:46And then it would close and the piston would rise on compression and power.
45:52And then at the end of the power stroke, the exhaust port inside the cylinder would line up with the rectangular port in the head.
46:00And what the Germans so delightfully call Auspuff, exhaust, would occur.
46:08Auspuff.
46:10Auspuff is nice, yep.
46:13Yeah, so it would generally run in parallel with crank.
46:18Yes.
46:20And as you say that the cylinder, the pipe, the pipe has a septum, a barrier.
46:28And on one side, the carburetor is on one side and it would go in that tube and kind of ricochet 90 degrees into the cylinder.
46:36Thing keeps turning, closes the chamber, bang, does its thing.
46:40And then when it rolls over, it goes out the other end.
46:44The cylinder has two ports in it, of course, an intake and exhaust port.
46:49So Norton got interested in this toward the end of their period of admirably intensive development and they built a cross-rotary single.
47:05And they were able to get up to the same power that they were getting from their factory poppet valve road race max engines.
47:13But because it took quite a bit of oil to lubricate this valve, it was hard for the engine to pick up when the rider wanted to feed power to accelerate out of a corner.
47:28I would imagine sealing that also would be a challenge, sealing that big long cylinder.
47:34You know, today they would surround the port with something very much like a Vonkel tip seal.
47:43And it would be like a piston ring made in any arbitrary shape, just like Honda's NR500.
47:51They said, why can't we make an oval cylinder?
47:54Well, it turned out they could.
47:56And the Vonkels, they have seals of all different weird shapes.
48:02Wonderful stuff that they did.
48:04Unfortunately, the tapering tips of the combustion space were quench areas.
48:15The cold metal had that part of the charge surrounded and it said, yeah, I was really hot to burn, but now I give up.
48:24And so you'd get unburned hydrocarbons out the exhaust.
48:31So all these things, some people will sort of tell you almost any idea can be made to work.
48:40But can we afford to make it work?
48:43Can we tool this thing for economical production?
48:47And whenever I see a world beating new engine designs, I think who's going to throw away their round cylinder poppet valve production line and give this a try.
49:01Someone's going to have to have some money, pretty serious money that they can afford to kiss goodbye.
49:09If it should turn out that way.
49:11Yeah.
49:13Well, there was also the Aspen valve, which was a cone.
49:17Yeah.
49:19The cone, as I understand it, was the chamber.
49:23Yeah.
49:25And it rotated, essentially the top of the chamber rotated.
49:29Yes, it did.
49:30Frank, Frank Aspen.
49:32Lined up with ports that were provided for that.
49:36And Veleset invested quite a bit of money in this thing.
49:42And Harold Willis was their competitions director and a very bright man and a word lover.
49:51I'm sure he eventually had some delightful things to say about the Aspen valve.
49:55But they were never able to bring it to workable excellence.
50:03It was like, yeah, we proved that you can make an engine run this way, but not as well as the engine that we already have.
50:12Particularly the excellent KTT 350.
50:17Yeah.
50:19Aspen had a 250 that he was spinning in 1937, 1940, they were spinning at 14,000 RPM.
50:29Sure, because no valve springs.
50:31No valve springs.
50:33And so you're balancing advantages and obviously, whatever it was, ceiling surface, too much oil, all the things that made that work were not enough of an advantage.
50:47People have tried to make rotating valves that have the same, that are sitting still during the high pressure phase, just like a poppet valve.
50:59And they're driven by something like all those Geneva stars that drive camera shutters, movie camera shutters.
51:11As the star rotates, it is driven by a pin on a wheel that goes into a space and then it sits still until the pin comes around again.
51:26So it's, it should have worked.
51:33But when you have going to have it sitting still and then accelerating violently, you're going to have the same problems of durability that you have with a poppet valve.
51:45So where's the advantage?
51:48But there are people who want to know.
51:51And so they keep on dragging out these old ideas, adding some modern materials or a modern lubricant or a modern sealing system.
52:00And they show this to the potential investors and they all go, oh, that's very interesting.
52:07Phil Vincent, he worked on one of the many barrel engines that has a series of pistons with a swashplate between them so that the pistons are all moving in a sort of sine wave fashion.
52:24AC compressors are like that.
52:27Yeah, very compact.
52:28Yeah, some of them, they say they're 10 cylinder, but really it's five and they're, but they're working on either end.
52:36And they just, they swash, they have a plate and it moves them back and forth.
52:40And that gives you your, you're constantly cycling pressure build and throwing it through your check valves and watching snowflakes come out of your air conditioning ducts in your 89 Ford F-250.
52:52Good one.
52:53Well, yeah, I was just going to say, we've got 53 minutes of air, a lot of air coming in and out.
53:06Yep.
53:0817 times a minute.
53:1017 times a minute.
53:12Well, as the late Kenny Augustine did, there have been a great many people who've devoted their lives to getting more air into engines.
53:25And Harry Westlake, an Englishman in 1926, bought three Sunbeam 500cc race engines.
53:38And one of them made 26 horsepower, one made 25 horsepower, and one of them made 29.
53:45And he wanted to know why.
53:47And he thought that it must have to do with their pumping ability.
53:51They were all had the same bore and stroke.
53:54They all had the same intake dimensions.
53:56But when he looked into it, he found that lots of small details in the shape of the intake port and the way the valve seat is cut and the way the valve seat blends into the cylinder head on the inside of the combustion chamber can exert a large influence on how much air enters the cylinder and is trapped there.
54:19So this is why people go to the airflow wizards.
54:23And it used to be, of course, you had to take your heads and they would grind every port.
54:30Nowadays, the wizard does one port and then they digitize that and the 3D machine does all the grinding.
54:43It turns the nasty parts of the port into powder.
54:47Yeah, those CNC porting machines are spectacular to watch and it just takes the tedium right out of it.
54:57Yes, indeed.
54:59You do it the one time, you make your art and then the machine replicates that for you and away you go.
55:04That means that you can then go down on the boulevard, order a very dark coffee, adjust the angle of your beret and be an artist.
55:13Well, air has mass. It doesn't like to turn corners.
55:17Ports need to be smooth. We need to get rid of usually the sharp edges.
55:23You got to pay attention to so much because air is invisible, but it's very clearly there.
55:32Yes, and it has an opinion.
55:34It does.
55:36Thanks for listening, everybody.
55:37Thanks for listening, everybody.
55:39Get down in the comments. We're still enjoying those. We have more ideas coming out of those for future programs.
55:47I was going to say the Yamaha R7, not the current twin-cylinder R7, but the homologation special of 1999-ish.
55:58This is something perhaps for a future podcast, Kevin, but why did that motorcycle sound so good?
56:04What was it about its intake valve timing, the length of its trumpets, the size of its airbox?
56:12I've ridden a lot of motorcycles and it's a quality of air. It's why the trombone can sound good.
56:20It was amazing. Maybe next time we can think about the sounds of engines.
56:29Oh, the sounds of engines is a wonderful topic.
56:33Indeed, it is.
56:35Thanks for listening, everybody. We'll catch you next time. Take care.