Kevin Cameron starts from the beginning of two-stroke exhaust expansion chamber development in the 1950s to the present. What were its origins and how did it explode power output in these simple, lightweight engines? How did we go from 8-hp single-cylinder commuters to 200-hp 500cc Grand Prix four-cylinders? Kevin knows, and Editor-in-Chief Mark Hoyer rides along with him.
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SportsTranscript
00:00:00Welcome back to the CycleWorld Podcast. I'm the Editor-in-Chief Mark Hoyer and
00:00:05I'm with Kevin Cameron our Technical Editor. We have a topic this week. Kevin
00:00:12will call it acoustical or excuse me acoustic supercharging and I will call
00:00:17it the origin of the expansion chamber. So what we're going to talk about is
00:00:20where did the two-stroke expansion chamber come from? The minds of geniuses
00:00:27of madmen. So it's a it's a topic you know you guys have been loving the
00:00:34two-stroke stuff the TZ750 and the RD350 and we thought we'd get into a
00:00:40detailed conversation about the origin of the expansion chamber. Before we get
00:00:45started we want to thank Octane Landing for sponsoring this episode yet again.
00:00:50You can click a link down in the description of this video and you can
00:00:55you can shop for a motorcycle and see about getting financing to assist you in
00:01:00your purchase if you require it. So click that link and check it out even just
00:01:05clicking on it would be a big help for us. The other thing I have to bring up
00:01:10is some of the comments or let me say one comment that I is near and dear to
00:01:16my heart. King Broslaw is his name. He said this is for all you on
00:01:24the streaming services. When are you going to tell the people listening via
00:01:28streaming services about your rad mustache? Friends, I have a mustache it's
00:01:35it's pretty uh anyway we appreciate the humor there and I'm also glad it's
00:01:42flannel weather here so you can see it. Flannel companies people are watching I
00:01:47was recognized at Road America driving a golf cart by a viewer who said I
00:01:54recognize you because of your flannel.
00:02:00Pretty awesome. All right let's just let's do this Kevin. Acoustic
00:02:04supercharging. So we all we all are used to expansion chambers that have a head
00:02:11pipe they have what you would call the divergent cone. Or megaphone. Megaphone
00:02:17yep and it swells up into a ball big big thing it's like a snake that's
00:02:22eating a rat and then it tapers back down with the convergent cone and then
00:02:27it goes out a stinger or we hope a muffler because they sound pretty nice
00:02:31with the right muffler sounds like mmm beautiful popcorn and yeah so we didn't
00:02:38always have that you know two strokes were lauded for their simplicity and but
00:02:44they didn't make any power when they were first first put into motorcycles so
00:02:48talk to me about that Kevin you you may know something about this. I might well
00:02:54first thing is that when the internal combustion engine the idea of burning
00:02:59the fuel in the cylinder rather than under a boiler full of water was put
00:03:06into real form the idea was the ideal was the steam engine which is not a
00:03:17four-stroke or a two-stroke it is it it has two power strokes per stroke
00:03:23because steam is admitted at both ends the piston rod goes through a seal gland
00:03:30on one end and the other end of the cylinder is capped by a plane cylinder
00:03:37head so they didn't want the idea of taking four strokes to get one power
00:03:44stroke didn't even occur to the early workers so two strokes were very common
00:03:50in early internal combustion engine development and a lot of them were so
00:03:55pitiful they were trying to use part of this of the stroke to fill the cylinder
00:04:02and part of it to to produce power and they ended up with almost nothing and of
00:04:09course many ideas start out that way what is now the semiconductor business
00:04:17can put billions of switches on a silicon chip whereas before it's this
00:04:24business started out with mechanical relays and then advanced the vacuum
00:04:28tubes as a means of switching and those things were huge they had hardly and
00:04:33hot yes especially air-conditioned rooms anyway the two-stroke idea got a lot of
00:04:42place in the early days before Otto had his explosive introduction to the
00:04:51success of the four-stroke Otto cycle Otto O-T-T-O yes and like many men he was
00:05:01fortunate to have an understanding wife he he was frightened by the violence of
00:05:08this thing I think he'd given it a little bit too much compression after
00:05:13all it was the first one ever and his wife when he got home listened to his
00:05:17tail and she said look just just sit down I'll make you something nice to eat
00:05:23and tomorrow you can straighten this all out and he did he did but the essentials
00:05:30of this two-stroke engine are these you imagine a piston at top dead center with
00:05:36mixture fuel and air compressed above it a spark or other means of ignition sets
00:05:42it alight converting it into high-pressure gas the high-pressure gas
00:05:46pushes the piston down if there's a connecting rod connected to a crankshaft
00:05:50it can accelerate the crankshaft if the rod connects to a water pump or any
00:05:57other useful device like that nothing rotates but the piston is on its way
00:06:03down being pushed by the expanding gas doesn't get too far before the pressure
00:06:08in the expanding gas drops to a point where it can hardly push the friction of
00:06:14the piston rings so at this point it makes sense to open the exhaust port
00:06:18even though there's still a little pressure in the cylinder so there's an
00:06:23a hole cut in the cylinder wall and as the piston uncovers the top of it what
00:06:29the German engineers called auspuff occurs out puff and when the pressure in
00:06:39the cylinder has dropped by means of this process which we call blowdown some
00:06:46other means of a means of pumping delivers fresh charge to the cylinder
00:06:53through one or more fresh charge ports now the problem is the cylinder at the
00:07:00bottom of the stroke is still filled with exhaust gas although at atmospheric
00:07:04pressure so by shooting in fresh mixture we're going to be diluted by
00:07:11exhaust gas and thereby lose power so very quickly everyone devoted a lot of
00:07:19thought to ways to let the fresh charge enter without quickly mixing and being
00:07:27completely diluted by the exhaust gas and we've all seen deflector piston two
00:07:34strokes the top of the piston has a wall across it on one side it may be a
00:07:40curved wall or fence this is the deflector on one side of the piston are
00:07:47the exhaust ports which in those days took the form of three or four round
00:07:52drilled holes because it was easy to produce 180 degrees from that exhaust
00:07:59port or array of ports was the fresh charge port or ports and they were a bit
00:08:06lower to allow the exhaust to blow down the pressure in the cylinder and a
00:08:14rotary blower a piston blower or some other form of blower would then push
00:08:22fresh charge in through those ports they would hit the wall the deflector on the
00:08:29piston and be guided upward hit the cylinder head flow over in reversing
00:08:38direction down toward the exhaust port and this by having the flow attached to
00:08:45the rear cylinder wall then to the cylinder head and then to the exhaust
00:08:49cylinder wall protected it to a great extent from exhaust dilution still it
00:08:58was a feeble feeble scheme and the extra surface area added to the piston by the
00:09:06deflector caused the piston to run really hot the central problem of all
00:09:12two strokes is that they're heated the piston is heated twice as often as a
00:09:17four-stroke piston so the problem is to cool the piston and this has remained a
00:09:28theme throughout the all of history of the two-stroke how many two-stroke
00:09:35pistons have been hold in this world many well the early schemes all depended
00:09:45on the idea of blowing fresh charge into the cylinder so that it would push
00:09:50the remaining exhaust residuals out and when they talking about that we're
00:09:57talking about a mechanical supercharger we're cutting yes I'm not a blower some
00:10:01kind of blowing it physically not relying on just like your normal
00:10:06four-stroke to have a you know some vacuum pulling it in it's actually being
00:10:09forced in through a pump of some kind people who are familiar with 671 blower
00:10:15that used to be used on so many top fuel drag cars that blower was used on
00:10:21a six-cylinder Detroit diesel two-stroke diesel and mounted on the side of it and
00:10:28it supplied air pressure to a chamber that surrounded all of the scavenge
00:10:35ports in that engine the exhaust ports were in the head and the fresh charge
00:10:41ports were a ring of holes at the bottom of the stroke so this was another
00:10:47step in segregating fresh charge from exhaust residual because it's leaving
00:10:53from one in entering from the other end so it's there it reduces the
00:10:59opportunities for mixing then somebody had the idea let's take that cylinder
00:11:04with the exhaust on the top and the fresh charge on the bottom and bend it
00:11:09in the middle and give the two cylinders that result a common
00:11:14combustion chamber I think Sears Roebuck used to sell pooch motorcycles and
00:11:21scooters that had this strange two-cylinder one combustion chamber two
00:11:28stroke engines I think they had a y-shape connecting rod oh yeah that's
00:11:32it's a thing of beauty if you've never seen that the Y shape it just looks to a
00:11:38person who's worked on you know regular old motorcycle engines with your typical
00:11:42you know connecting rod when you see a y-shaped connecting rod you just think
00:11:46what what horror is this well the the idea of uniflow scavenging exhaust
00:11:59leaves from one end of the cylinder fresh charge comes in at the other
00:12:03continues to this day as the power plant of world trade enormous marine
00:12:09diesels making up to a hundred and twenty thousand horsepower powers all
00:12:14the ocean ships but back to practicality how can we make a motorcycle and how can
00:12:24we get rid of the excess heat absorbed onto the piston by that deflector and a
00:12:31diesel engineer named Adolph Schnurla had this idea he said to himself okay
00:12:36here's the exhaust port at one side of the cylinder and on either side we'll
00:12:41make transfer ports that are aimed away from the exhaust at the opposite
00:12:46cylinder wall and the flow from them will hug the piston so that again the
00:12:52flow will be attached to a surface flows across the piston to the rear cylinder
00:12:57wall up across the underside of the head and down to the exhaust no
00:13:02deflector a flat-topped or very slightly domed piston it was a great success this
00:13:11was called Schnurla scavenging and it didn't require u-shaped cylinders or
00:13:17shared at cylinder here's mine no mine and it didn't take all the power out on
00:13:24the exhaust piston so but again the problem with this engine was how are we
00:13:33going to pump fresh mixture if we don't want the complexity of a bore DKW had
00:13:41built very powerful twin piston racing engines in the 1930s they claimed they
00:13:50could hear them on the mainland of Britain all the way from the Isle of Man
00:13:56they used at first a giant piston blower a reciprocating piston then they used a
00:14:03rotary blower when the war ended and the International Motorcycle Federation wrote
00:14:11new rules for racing they allowed two strokes to have the same displacement as
00:14:18four strokes and the reason they did so was one they were just such pitiful
00:14:24smoky pieces of junk and two they used the underside of the piston as their
00:14:35scavenge pump when the piston rose it created a partial vacuum in the crankcase
00:14:42a carburetor connected to that crankcase flowed mixture in when the piston
00:14:48started down its skirt closed off that carburetor port and compressed very
00:14:55slightly the mixture in the crankcase allowing cup handle shaped ducts to
00:15:01transfer the mixture in the crankcase pump yes like that much like this coffee
00:15:07cup I'm holding a coffee cup folks to show this is descriptive audio again to
00:15:12show this show the handle the curved handle that's where the transfers
00:15:16basically are on the sides of the cylinder and that'd be a whole
00:15:19discussion in of itself aiming direction the transfers will point in the cylinder
00:15:25that's later in this many workers many hands this whole process took from 1949
00:15:33until the two-stroke dominated all FIM classes in 1975 so that was a good long
00:15:40time in development but the FIM the International Motorcycle Federation gave
00:15:47the two-stroke even Stephen displacement with the four-stroke because it couldn't
00:15:53pump any more than its own displacement by using the piston the underneath of
00:15:59the piston as a scavenge pump so this engine it's hard to imagine a simpler
00:16:06engine and DKW produced hundreds of thousands of RT 125s you can see one in
00:16:15the Barber Museum down in Alabama and it produced about 4 horsepower at 4500
00:16:23rpm so this was no hold on to your hats machine this was minimum motoring but
00:16:31the presence of the Luftwaffe in so many parts of Europe meant that these
00:16:37motorcycles were loaded into the bomb bays of any aircraft that would carry
00:16:43them because men in the soldiery always need cigarettes and beer and if you've
00:16:51brought a little motorcycle with you and you have access legal or illegal to a
00:16:58source of fuel you might be able to scare up some of those necessities so
00:17:04after World War two it was the most copied motorcycle ever there were
00:17:10Spanish copies the British copy was called the BSA Bantam the American copy
00:17:15was the Harley Hummer and several Japanese makers started out and this
00:17:23includes Honda building two strokes based on the RT 125 just worked out
00:17:30that way because what the world needed in 1945 was a way to get from A to B
00:17:37without having to walk it the whole way so now began the problem people in East
00:17:46Germany of course being persons of analytical mind began to consider the
00:17:54problem of racing the war was a drag and post-war rationing is isn't much better
00:18:03so we better go racing in order to take our minds off these other problems and a
00:18:09fellow named David Daniel Zimmerman began tuning RT 125s and he soon found
00:18:18that a rotary disc with part of it cut away made an excellent intake valve
00:18:27because you could have any timing you want if you use the skirt of the piston
00:18:32to uncover an intake port that gave only symmetrical timing if it was 101
00:18:40degrees before top center it was a hundred closed 101 after so that was
00:18:46Zimmerman's contribution disc rotary disc valves had exist before the Sun V
00:18:52test motorcycle had one but he gave it a racing application he also turned the
00:19:00cylinder around so that connecting rod side thrust pressed the piston against
00:19:05the exhaust port improving the seal and the cooling of the piston so at a point
00:19:16the official impetus was put behind a company called IFA and they thought IFA
00:19:24should go racing and so the Stasi went and had a conversation with mr. Zimmerman
00:19:30they said you will hand over all notes prototypes racing machines etc and all
00:19:39parts and you will forswear contact with motorcycles for the rest of your life
00:19:44agreed he readily agreed what choice did he have and so development of the two
00:19:53stroke at IFA which shortly became MZ Motorrad Jopau in East Germany move
00:20:04forward meanwhile DKW in the West western part of Germany was also racing
00:20:13two-strokes and in the late season of 1951 an engineer named Erich Wulf decided
00:20:26that he was going to look into the question of why two-strokes don't make a
00:20:33lot more power than they do he knew that many racing two-strokes had a header
00:20:41pipe that came out of the exhaust port and went to a megaphone and a megaphone
00:20:46is basically a means of turning a positive pressure wave which is the the
00:20:53house poof or blowdown reversing its sign and by making a megaphone you
00:21:00presented this pulse to a larger area of atmosphere so that the expansion pulse
00:21:09or low-pressure pulse went back up the pipe and into the cylinder now we're not
00:21:15only using the scavenger pump to push fresh charge into the cylinder we're
00:21:21also creating a partial vacuum in the exhaust pipe which is helping inviting
00:21:26all those hot buzzing molecules wouldn't you like your freedom come this way so
00:21:33this double whammy ran into a big problem because the engine revved up
00:21:43until the amount of exhaust lead the degrees between exhaust opening and
00:21:50transfer opening became too little to let the pressure out in time for the
00:21:56transfers to start pumping fresh charge in well let's raise the exhaust port
00:22:02then what happened then was that with the megaphone exhaust and the piston
00:22:08just now coming up to close the exhaust port it's already closed the transfers
00:22:13now the exhaust port is poking up above the piston it's pumping the mixture back
00:22:18out and the exhaust pipe with its megaphone is still going come hither I've
00:22:25got something for you so this meant that in the immediate post-war years the
00:22:33two-stroke single let's say a 125 was stuck at between 8 and 12 horsepower and
00:22:40about 7500 to 8000 rpm if they raise the exhaust port they lost charge if they
00:22:48ran that exhaust port at the normal 17 degrees or so the engine was weak and
00:22:55only made this very limited power now what so Forth had no doubt had a look at
00:23:06books such as this this is Schweitzer's scavenging of two-stroke diesel engines
00:23:13and there's a special chapter in here this is a 1949 book on the use of
00:23:20exhaust energy as a means of improving scavenging 1949 before that Michel
00:23:29Cadena see who had proposed the use of the exhaust to generate low pressure in
00:23:37the cylinder to invite the fresh charge in so there was a lot of discussion
00:23:43going on about this Eric Worf was not a gyro gear loose trying one crazy thing
00:23:49after another until he stumbled across the truth he was working with definite
00:23:54ideas his idea was we'll put a stopper on the end of that megaphone so that it
00:24:01doesn't lose as much fresh charge and the stopper was a little abrupt so they
00:24:08instead they pulled the middle of it out to make a convergent cone and that's
00:24:15what ran on DKW's 125 factory racer at the end of the 1951 season well did DKW
00:24:28become world champions overnight they did not they stayed with the original 17
00:24:36degrees of blowdown even though they had a means of preventing charge loss and
00:24:43if this was so radical imagine this DKW's three-cylinder 350 turning 10,000
00:24:52rpm maybe even a bit more unable to defeat Moto Guzzi's rather vintage
00:25:00looking horizontal single single cylinder four-stroke embarrassment how
00:25:10can this be well along came Walter Codden who'd worked at Peenemunde the
00:25:21rocket research center of Germany during World War two we don't know whether he
00:25:28emptied trash cans or whether he was involved at some level in the thinking
00:25:34process but he had certainly been exposed to the the roar and the drone I
00:25:41think of him as not the inventor of the modern two-stroke but as the systems
00:25:48integration officer his job was to bring together the rotary disc intake Daniel
00:25:59Zimmerman's other big invention which was very tiny needle rollers in the big
00:26:04end of the connecting rod they lived bigger rollers failed they turned blue
00:26:09and squashed out into sharp-edged pancakes I think what Codden's people
00:26:19were able to do he worked with one or two others was to discover that they
00:26:26could extend the blowdown they could raise the exhaust port without losing
00:26:33charge because they had the counter comb the Germans called it a gegen konus
00:26:39counter comb to stop reflecting back a negative wave which would tend to pull
00:26:47exhaust or tend to pull fresh charge out of the cylinder and substituted a
00:26:53counter cone which would reverse the signal again and send back a positive
00:26:59wave shutting the gaseous door yes absolutely acoustically providing an
00:27:06acoustic door and it did more than that because if you imagine what's going on
00:27:11in the cylinder the suction if you will from the megaphone part of the exhaust
00:27:18pipe is pulling fresh charge into the cylinder and into the header pipe and
00:27:24now the piston is rising it's closed off the transfers and there's still exhaust
00:27:28opening left now this pressure wave comes back from the counter cone and it
00:27:36pushes that fresh charge in the header pipe back into the cylinder the exhaust
00:27:43port closes the cylinder is now much better filled with fresh mixture there's
00:27:50a lot of exhaust gas in there still but there's been a gain so by 1958
00:28:00Walter Codden of MZ was able to build a 125 single that made decisively more
00:28:08power than the best 125 four-stroke single and that company's twin-cylinder
00:28:14two-stroke 250 was making 48 horsepower which was certainly competitive the
00:28:23problem was that East Germany was economically feeble at this time it was
00:28:32not a post-war return to health dynamic economy like West Germany and so Codden
00:28:45if Codden's R&D program was himself and one or two other fellows and whatever
00:28:52funding they could wheedle out of their Stasi advisors that was up to up to them
00:29:04so there were some stunning results really wonderful performances from MZ
00:29:12motorcycles but in the meantime that these new two-stroke concepts fell into
00:29:21the hands of companies that had serious R&D power namely Yamaha and Suzuki I'm
00:29:30going to leave out of this discussion all of the talk about Ernst Degner
00:29:34defecting to the West with his all kinds of drawings and cylinders and so forth
00:29:41stuffed under his shirt that's another matter entirely but what happened was
00:29:47that once Yamaha got hold of these ideas they quickly mastered the problems
00:29:55that MZ had been unable to namely piston and cylinder metallurgy they
00:30:02created controlled expansion alloys that did not immediately seize when they made
00:30:08more than four or five horsepower and that was essential because one of the
00:30:14Suzuki engineers described their problem he said our pistons swell like a cake in the oven
00:30:21food analogies can't can't miss yep but in 1962 at Spa Francorchamps in Belgium
00:30:37riders Sunako and Ito on Yamaha RD-56 machines just steamed away from the Honda
00:30:48Force they just left them for dead and Honda engineers realized oh this is a big
00:30:59problem we're going to need more cylinders more RPM more everything and
00:31:05the result the direct result of seen Sunako and Ito's one two was the Honda
00:31:13six the 256 because four strokes combustion pressure unsupercharged is
00:31:23limited by the atmosphere's pressure 14.7 psi so that's fixed displacement is
00:31:29fixed the other variable among the three that make up horsepower is RPM so
00:31:35Honda had to set sail for 20,000 meanwhile thank goodness I mean what a
00:31:42what a thing to what a sound addition for pushing yeah just well I mean it
00:31:47pushed four strokes and you know two strokes kept going but it pushed four
00:31:51strokes and we got some beautiful things out of it tiny little pistons teensy
00:31:55little spark plugs tiny little valves all going yes you know making a symphony
00:32:02of inline sixness pistons performing their stroke 300 times per second
00:32:11amazing I yeah I think I you know it I want to do a podcast sometime on the
00:32:18inline six and why I I think it's the perfect engine but that's me well no
00:32:25question that it is a very distinguished engine because once they
00:32:30got it working and it took them a while they introduced it at Monza in 1964 and
00:32:41not until Hale would got on the 256 and the 297 six-cylinder 350 they became
00:32:54Hale would was was unbeatable he won 250 and 350 in 1966 and 67 so that was a
00:33:02black eye for the two-stroke folks anyway what happened of course was that
00:33:09these engines were just refinements of the original Daniel Zimmerman engine
00:33:17with with three transfer ports the ones on either side of the exhaust port plus
00:33:24one opposite the exhaust sort of aimed up at the cylinder head but soon Yamaha
00:33:33and Suzuki began to refine the shapes of exhaust pipes and the shapes direction
00:33:41and number of transfer ports and the result of that work that intensive work
00:33:50over a period of years was that when the two-stroke era ended with the coming of
00:33:58MotoGP 125 two-strokes left the scene in what 2012 I think they were making
00:34:10nearly 60 horsepower or 12 times the pitiful smoky power of 1949 amazing and
00:34:21the shapes of things had changed a great deal as Dutch tuner and engineer
00:34:30Jan Thiel has said we really started to make serious power when we adopted the
00:34:40cup handle style transfer ports rather than the the more common ones which went
00:34:47up each side of the cylinder and then suddenly it turned at 90 degrees and
00:34:52attempted to enter the cylinder abruptly in that way and of course what that does
00:34:58is it's just like in a four-stroke intake port on the far side the flow is
00:35:04high velocity highly efficient on the near or short side there may be almost no
00:35:10flow at all because the turn that you're trying to make the air do is just too
00:35:15abrupt it can't do it you're basically you're almost making you know after the
00:35:22turn you're effectively reducing the size of the port because it's blocked by
00:35:27all the momentum it's all the slum to the outside yeah we're talking about a
00:35:32curved transfer that's like the cup graceful graceful curve because air air
00:35:39air needs that air as mass and momentum and all the things that happen with with
00:35:44making it flow it near supersonic speed sometimes and having that curve allows
00:35:50the air to do its thing whereas the old transfers or the ones on an art like a
00:35:56parallel twin you know they they're 90 degrees they are sharp turns and it just
00:36:01doesn't flow right and just doesn't tell you what you want and this is why then
00:36:06yep this is why a big step forward for 250 twins in GP racing was to take the
00:36:16two cylinders and swing them apart 90 degrees that made room for all the
00:36:23transfer ports you could all the cup handle transfer ports you could want
00:36:27Evan took his fingers and made a parallel twin and then he crossed them
00:36:30over to make it a V twin and then you had room on the sides of the cylinders
00:36:34instead of having them smashed up against each other you had room on the
00:36:37sides of the cylinders put those transfers in to make it make it flow I
00:36:41want to get some yeah I want to go back to the the basics of what we're talking
00:36:46about to help people visualize you know a two-stroke has a solid cylinder head
00:36:52with a spark plug usually centrally located in a little dome a lot of squish
00:36:58and then a ring of squish a ring of squish which is just a squish is an area
00:37:04of the cylinder head that is really close to the piston when the piston
00:37:09reaches top dead center it might be if you're fancy it might be twenty eight
00:37:14thousandths of an inch the clearance yeah very very close and if you're on
00:37:18tenths of a millimeter yeah and if you're running your you know your pre
00:37:24unit triumph with aluminum connecting rods you're probably not going to go
00:37:28under forty thousandths of squish but you're making the piston get really
00:37:31close to the cylinder head and they call it squish because it squeezes the
00:37:36mixture out from the edges of the piston to where the spark plug is especially in
00:37:40a two-stroke centrally located bang and it's right where the fire is being lit
00:37:45so that gives a last-minute stir and it yes homogenizes it mixes the fuel and
00:37:52the air really well and it jams it right up against the sparking device
00:37:57which is great so that's all we have the two-stroke is the piston is the valve
00:38:04essentially we can talk about we can talk about reeds and all the other
00:38:07things but if you took if you if you just put the piston at the bottom bottom
00:38:13dead center and blew through the carburetor it's gonna go in and out it's
00:38:20just gonna you have an exhaust port and you have transfers and there's nothing
00:38:26to stop at the piston has to block those and that's the whole trick with
00:38:29two-stroke timing is when is the exhaust port open unblocked by the piston when
00:38:36are the transfers unblocked because you have to close that off the only time the
00:38:41engine can make power is when the valves are closed right so it's and the piston
00:38:47is the valve here in this case and so yes it is that's this is the whole trick
00:38:52and you know Kevin's talking about mixture firing into the cylinder and
00:38:59going out the exhaust port if it if it's not timed right and if you don't have
00:39:03the expansion chamber sending a pulse back to shut the door and to do it to
00:39:10open it and to invite it out and then to shut it to keep this this is the reason
00:39:16for the ring ding idle which four-stroke which nervous four-stroke
00:39:23enthusiasts like to make fun of because what happens is when the engine is
00:39:30operating on very low throttle you're squirting a little small volume of
00:39:34mixture into a cylinder filled with exhaust gas is the fresh charge anywhere
00:39:41near the spark plug when the spark occurs probably not well another stroke
00:39:49and it will have squirted in a little bit more fresh charge all that time it
00:39:54there wasn't any near the spark plug either a third revolution and a third
00:39:59injection of fresh charge Oh pop it gives it fires weekly and so it takes
00:40:07several revolutions of the crankshaft to accumulate enough idle mixture in the
00:40:12cylinder for the spark plug in the mixture to be in the same place so it
00:40:18sits there going pop pop pop pop pop and does not give you an inkling of what
00:40:25will happen at Daytona
00:40:29an amateur built motorcycle that of Nick Ricchetti who who delivered orange juice
00:40:35in New York City as a means of income he went through the timing traps at 183
00:40:42miles an hour on his TZ 750 operating on this foolishly simple principle which
00:40:52had been so refined that it worked quite well over a narrow range of rpm well
00:40:59that's the real point here is that this acoustic supercharging is tuned to make
00:41:07power it can't work across the entire I mean without what would you do they
00:41:12tried many different things to change the waves like water injection to change
00:41:16the density of the exhaust resonators resonators they started yeah they
00:41:23started moving exhaust ports you know that was the power valve eyelid exhaust
00:41:28ports yes and so that was an attempt because in the in the strictest
00:41:33mechanical you you put it to me when we were reporting my RD 350 is that
00:41:39whatever it was you know we had talked about the power band and and I wanted
00:41:44torque and you said yeah my engines have always had torque and you were talking
00:41:48about I was talking about like oh I'm building a street motor it's 4,000 you
00:41:52know it's five to seven I want you know this nice strong mid-range torque and
00:41:57you're like five like you just looked at me like I was insane and because it
00:42:02was you were making whatever it was six to ten or seven to ten or something
00:42:06seven seven to ten seven to ten so between seven and ten you said that's
00:42:11it's time to cut wood that's when you know that's when the motors that's when
00:42:16that's when the tuning of everything yeah yep yeah all the waves are doing
00:42:23exactly what you want them to when you want it to happen and you're pulling in
00:42:27a tremendous amount of fresh charge and then you're pushing it back when the
00:42:32wave you know if it's coming out the exhaust port a little bit that wave
00:42:34comes and knocks it back in there and that's when you're making all the power
00:42:38and you can expand that a little bit with power valves and other other things
00:42:43but really it's just time to cut wood and the thing about this is anyone can
00:42:50do it and that was the point of the late Gordon Jennings's book two-stroke
00:42:57tuners handbook it basically said here are a few simple ideas and a few
00:43:03elementary numbers that will enable any person of curiosity with any talent with
00:43:11you know any manual dexterity to have a fast two-stroke motorbike this is not a
00:43:20matter two-strokes were not developed by mathematical models mathematical
00:43:28models may have helped years later but the basic work was what the chemists
00:43:34call combinatorial analysis try everything there were two guys in the
00:43:42basement I don't know there's HRC or a previous organization whose job was to
00:43:47get the horsepower out of engines that the engineers had finished designing and
00:43:52you can bet that some of those new designs came into their department and
00:43:57they looked at the cylinders and then they looked at each other like what but
00:44:04they quickly got to work trying lots of different exhaust pipe dimensions and
00:44:10transfer port aim transfer port size transfer port timing until they got a
00:44:17glimmer and I once had a phone call from a man who was participating in grass
00:44:26drag racing on snowmobiles and he said I'm almost there but I'm not there can
00:44:36you help me and I said well one of the things is that mixture that is caught in
00:44:42the squish band burns late because flame doesn't transfer into a 28,000 gap very
00:44:52rapidly so you may be using too much squish too wide a squish band
00:44:58unfortunately the only way you can vary this is to make different sets of heads
00:45:06all with the same squish clearance but with various widths of squish band and I
00:45:12described how he might do this and I didn't hear from him for several months
00:45:18and he called me and he said I'm now the dominant force in my sport because he
00:45:25was willing to make those repetitive experiments until he got somewhere and
00:45:32he got where he got to was the top and there were lots of people messing with
00:45:40two-strokes kelker others mess with him he's the one who teamed with the late
00:45:46Don Vesco in 71 I think and he said Don had this primitive dyno back in a
00:45:56storeroom somewhere and I I got the thing out and set it up and built a test
00:46:02engine that I could put it one cylinder on and he said I started finding things
00:46:08out and he found things out to the point that when Kenny's 250 was out qualified
00:46:18in 1976 Kel must have said oh all right and he shortened the header pipes 20
00:46:29millimeters in each exhaust pipe he took 25 thousandths off of the cylinder head
00:46:35and recut the water groove water seal groove these were liquid-cooled TZ 250s
00:46:41and he raised the exhaust port and widened it a millimeter on each side now when you do that
00:46:54those cylinders were chrome-plated today we have Nikasil which is more durable but with chrome
00:47:00you cut it it means a 900 mile cylinder becomes a 300 mile cylinder but what do we want beautiful
00:47:09cylinders or races one you know it's like now with with saving the planet you want to save the
00:47:19planet it's going to cost you no solar arrays aren't free well Kel knew that making those
00:47:30changes would completely transform the stock engine and they did and the proper order of
00:47:38things was restored and I doubt that it took him half a shift to make those changes so two strokes
00:47:51if you if you collect a few exhaust pipe dimensions there's some and there's an excellent Australian
00:48:01book that has all the TZ Yamaha exhaust pipe dimensions with the aid of that you can make a
00:48:09pipe that will be close for any cylinder and similarly you can get close on port timings
00:48:20this is not an arcane secretive cult of unknowable beings in tall pointed purple hats
00:48:32it's just stuff we humans do you can do it too yeah and I think that the lessons that were
00:48:49learned in two-stroke GP racing have now found a place to live in competitive snowmobiles and
00:48:57outboard racing and other places where the beat goes on but of course the problem with street
00:49:09two-strokes the reason that after 1984 approximately they disappeared as a road going vehicle is that
00:49:18there is mixing between the fresh charge and the exhaust and some fresh charge goes out the exhaust
00:49:24about 30% of it and becomes unburned hydrocarbons that are detected by the the people up in Ann
00:49:36Arbor and they say you can't run that in this country and clean that model up or be gone now
00:49:44one way to deal with that is to say oh we'll put the fuel in after the piston has closed the
00:49:51exhaust port so that's direct injection that automatically means no lost unburned hydrocarbons
00:50:00another method is to identify that part of the transfer stream that will never reach the exhaust
00:50:09port by the time until after it is closed and that's transfer port injection Bombardier builds
00:50:15engines of that type there are a few European two-strokes that employ these two principles so
00:50:21the the two high power two-stroke is not dead it's just hibernating yeah this is the specific
00:50:33horsepower is still a winner the weight I mean it just it's it's great like if four-stroke
00:50:41motocross bikes and Enduros are magnificent and a lot of fun and and a good 350 ktm or 500 ktm is
00:50:50a you know four-stroke is a magnificent motorcycle but then you try a 300 cc two-stroke that they're
00:50:57making also and you see the light as Malcolm Smith said weight is the enemy ultimately weight
00:51:08is the enemy and he's so right because you get on a 300 two-stroke and you just think this is
00:51:13the greatest dirt bike in the world this is the most magnificent motorcycle for traversing any
00:51:20terrain it's just magnificent really is you know so when we're talking about resonate the
00:51:28resonation of the pipe and the waves you know we're talking about you always talk about pipe
00:51:35organ you know it's a pipe organ the pipe makes a nice note plays a single note a bottle if you
00:51:42blow across the top of a bottle the volume of the bottle determines the tone with the air going
00:51:50across the opening so if you made a roll it up a quarter of the way in it the pitch rises rich
00:51:55rises or you change the size of the bottle and it will make a different tone big big bottle low
00:52:00tone got to push a lot of air to make it resonate and that's what we're talking about with the
00:52:05expansion chamber it completely changed it really changed transportation for us you know
00:52:14it really made such a simple engine move the world because it was easy to manufacture and
00:52:19and we could make a little bit more smoke back then we didn't we hadn't I hadn't cleaned our
00:52:29act up yet and that's what happened to the two-stroke as you were just pointing out you
00:52:33know it was more difficult to control emissions you're putting oil into lubricate oil you know
00:52:41you had oil injection or you're mixing oil in your gas and it's going in to you know first
00:52:45thing it does is hit those bearings in the bottom end and keep them from locking up yeah and but
00:52:54it's it's also gonna burn some of that so that was our particularly our hydrocarbon problem with
00:53:01the two-stroke and that's why when you said to me about my RD 350 and how I said something around
00:53:096,000 or 5,000 rpm and you said well you'll find that it won't run particularly well down at that
00:53:15rpm and you're going to get terrible fuel economy because it wasn't keeping all the gas and it
00:53:23wasn't burning the gas it was it would send it when it's off of its happy tone off the pipe off
00:53:31the pipe fuels fuels just going into the exhaust pipe unburned and this is why when I first started
00:53:39measuring all the fuel that went into the race bike fuel tank and then measuring the fuel left
00:53:47at the end of the day I really learned something what I learned was the greatest fuel consumption
00:53:54occurs in first practice and I was in Europe in 81 with a rider who had not ridden on those circuits
00:54:03so he was learning the circuit in first practice fuel consumption was high second practice fuel
00:54:09consumption came down a bit lowest fuel consumption of all in the race itself because once the rider
00:54:17had got the range so to speak knew what to do what the swear the circuit went how to keep the
00:54:26engine in the power band instead of this mixture going out the exhaust pipe it was being trapped
00:54:33in the cylinder and burned to produce power now reed valves there has been a lot of talk about
00:54:41how reed valves were going to make this wonderful broad-range two-stroke it's a two-stroke with
00:54:47two natures below the pipe it is only the crankcase acting as a pump that is moving mixture
00:54:56so yes the engine will run but if it's a piston port or if it's a rotary valve timed for high
00:55:07speed at low speed it will push a lot of mixture back out so a reed valve improved that situation
00:55:14made the engine more drivable below the exhaust pipe resonance but the actual power band was
00:55:24still determined by the pipe because for example when Honda put motocross large area reeds on the
00:55:32cylinders of freddy spencer's 1982 ns3 500 triple power band was 9800 to 11,000 1200 rpm just like
00:55:48with a tz 750 just like with any two-stroke then you start adding devices like the variable exhaust
00:55:56port timing exhaust resonators cooling the exhaust gas in the pipe with water injection
00:56:03to make it resonate at a lower frequency you can extend the range to a useful extent but not all
00:56:13that much which is why when moto gp began in 2002 the big difference was with four-stroke you could
00:56:23start to feed power from the apex even before the apex because you could feed gradual smooth
00:56:32power with a two-stroke there was nothing until you open the throttle a fair amount and then it
00:56:40started to eight stroke pop pop pop pop and then to four-stroke and finally to two-stroke and at
00:56:49each step there was a sudden step up in torque so that's why you saw riders like mcduin
00:57:00holding the motorcycle radically more upright than their own bodies which were offset into
00:57:06the corner so that there would be enough tire that when the engine hit the pipe
00:57:12the tire would drive the motorcycle forward rather than spin
00:57:15a lot of high sides in those days right in those days yes in fact the fim told us that if
00:57:24the high sides weren't brought to a close that they would first impose
00:57:31minimum weights and then intake restriction as the ama had done um was it 78 sometime like that um
00:57:45at daytona because kenny had said we're getting sideways past start finish and
00:57:53something bad could happen ama were
00:57:59chewing their nails so um they only got as far as the uh increased weight minimum
00:58:08no intake restrictors for the fim because the manufacturers responded quickly with torque
00:58:14controls they simply uh reduced the amount of torque that was available in lower gears where
00:58:21it's easy to spin the tire and where and thereby they limited the hit as the engine rpm rose uh
00:58:31onto the pipe and savvy riders like mcduin and uh mike baldwin took care to ride the engine in its
00:58:41linear range that is in the range controlled by the exhaust pipe on a tz750 that meant between 9300
00:58:51and 10-5 or so unless you had somebody else's exhaust pipes on there blocking out the entire
00:58:59tack except that area yes because it's the area of interest the idea of trying to
00:59:08dump truck your way off of corners at 6000 rpm no because when you hit 9300 rpm the torque is
00:59:16going to double and you're going to tip over yeah it spikes so fast it starts it becomes
00:59:23it just goes yeah yeah that was the old schwantz roll you always talk about you know kevin would
00:59:30have a lot of throttle and then as the bike is coming in and coming off the corner he's actually
00:59:36rolling the throttle closed to try and make the torque output more linear though the power is
00:59:41steadily rising yeah rolling it back to keep it from rising too much yeah and uh
00:59:51uh those primitive torque controls and uh other electronics of the 1990 period
01:00:00soon were elaborated into the electronic rider aids of the present era old-timers didn't like
01:00:07them at first oh it interferes with the rider's freedom and it's a existential issue and let's
01:00:13take several college courses but uh then they got to kind of like it yeah well always everyone
01:00:24fellows at bmw people on staff who rode but were not um competition riders found they liked rain
01:00:32mode on their new zippity-doo four strokes because it made them feel more secure motorcycle wasn't
01:00:43going to get away with them now you see him now you don't yeah yeah it was a it was a it was a
01:00:53magical uh time if you weren't one of the riders getting hurt by the motorcycle but look i remember
01:01:00going to laguna seca camping at laguna seca sleeping on rocks because we got there late
01:01:06on a hillside in a tent there were no good campsites left so we were camping on on a hill
01:01:12with rocks on it and um it was sort of 88 89 i went both of those years and uh
01:01:20i would always walk a lap of the track during practice so i would practice would start and i
01:01:26would just walk the entire circuit across the bridge i probably saw you then yeah i'd like to
01:01:32do that too yeah you want to see you want to see folks go through six at laguna because it's a neat
01:01:38fast corner you want to see them drop through the corkscrew and you want to see you know between
01:01:43four and five that's a that's a really neat shoot and then five is a much faster corner than you
01:01:49might imagine you know it's kind of banked and it goes uphill at laguna and walking between four
01:01:53and five is when i saw kevin schwantz crossed up wheelie spinning the back tire with the bike's
01:02:00front wheel in the air on his pepsi suzuki weaving between four and five on the back wheel driving
01:02:07out of that corner it was it was a thing of beauty watching uh who was i think it was ron haslam
01:02:13uh on the kojima get or no it was uh mamola i think uh off into the dirt in six
01:02:22massive tank slapper broke the windshield goes back on the bike on the track heading toward the
01:02:30corkscrew without skipping a beat just immediately tucked completely fully tucked in behind a broken
01:02:37windscreen with the throttle backed wide open like i'm back back on pace i'm going through the
01:02:42corkscrew next that's behind me so it went well awesome yeah sorry go ahead it has been uh noted
01:02:54by uh ben spees who rode uh in that era that uh the extreme torso offset practiced by riders like
01:03:09jorge martin and bastianini would simply not have been possible on two strokes because the rider's
01:03:20ability to control the motorcycle was incompatible with having one arm stretched
01:03:27across the top of the gas tank and the other shoulder on the track surface
01:03:32uh that that kind of the two-stroke slip and grip corner exit would just shake the rider off
01:03:41the rider had to take care to stay on the motorcycle
01:03:50yeah um this reminds so we're talking about rider aids and the way the power is coming in
01:03:57uh all we've sought with all of these electronics is smoothness of application at the lowest
01:04:02traction point right you're trying when the maximum lean when you introduce the throttle
01:04:09you want that to be as perfectly smooth as possible and it was uh this is perhaps another
01:04:15show we were sitting with romano abesiano uh yeah and we were talking about he's a he's
01:04:24he's much like you kevin in the sense that he's a polymath and uh as far as as engines and and
01:04:30things metallurgy you guys were talking about rail locomotives and aircraft and this beautiful you
01:04:37know you guys just were off on a lot of tangents and it was beautiful uh but what he said was well
01:04:43we have we were starting to talk about the electronics in play on the aprilia and he said
01:04:49well the first thing that happens is we have a map that takes up the slack in the gear train
01:04:57the first application the first application of the throttle by the rider has a map that takes up
01:05:04from deceleration to acceleration in the drive train to be normally there would be a clunk there
01:05:10when you when you first move the throttle it would go clunk you don't want that at the apex
01:05:14you don't want the clunk you don't want yeah you don't want uh you want that to be perfectly
01:05:19smooth no and when we're talking about tiny tiny changes in mass reverberating through the drive
01:05:27train which they are eliminating with electronic controls with very precise i mean it's just it's
01:05:35crazy good and it's related it is related to the two-stroke expansion chamber because
01:05:41what a nightmare it was to uh to try to control that throttle off the apex you know and and all
01:05:46that stay within the to stay in in sync with the with the organ pipe yeah
01:05:55well thank you very much for listening folks this is the uh we're we're going off the pipe now
01:06:02we're gonna go whoa we're bogging off the pipe um it's uh that's the two-stroke expansion chamber
01:06:11what a uh what a thing what a change it made to uh smoky little dirty little two strokes to uh
01:06:21beautiful high specific horsepower and a sound so many of us uh grew to know and love i still love
01:06:27it i have an rd 350 it's time to fly back and make pipes kevin making those pipes was was good
01:06:35once they were finished you could look at this smooth shape that you'd made yeah the exhaust
01:06:41poured all the way back to the rear wheel and not think about the 32 welds each one of which had to
01:06:48be tapped and hammered and body worked into a smooth curve because what you don't want is an
01:06:54exhaust pipe that looks like the tin woodman no a series of clunky joints well it was who who
01:07:04who was doing that um there was a company that began hydroforming oh lovely lovely yes hydro
01:07:12forming their expansion chambers and it made more power to not have the seams and the steps
01:07:19you have a continuous flow curve yes smooth curve it it uh it just made more power you could make
01:07:25the pipe in basically the same dimensions but the the hydroformed one was more uh more better
01:07:32and of course botaco had a certain guy i have his name in notes who formed the pipes for tss race
01:07:41bikes from halves and those halves were hand formed into expansion chamber shape so that
01:07:50a slight taper from the cylinder then the megaphone part then the center section the
01:07:56convergent all one piece i would like to shake his hand pardon me yes yeah i would like to shake that
01:08:03guy's hand and talk to him because that sounds exactly like the very troublesome problem that
01:08:09i'm somehow drawn to try to solve i don't know why but uh all right well thanks for listening folks
01:08:16um and we will uh catch you next time