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Thread: ESE's works engine tuner

  1. #15331
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    Do you see what I'm trying to say about the 18mm plugs having more space around the center electrode for the A/F charge to swirl around? Since all of the related events are happening in an extremely short time, I'd think this would give a slight advantage.

    HOWEVER, after I left the computer yesterday, it occurred to me that you biker guys probably don't ever run the recessed-gap plugs that outboard racers often use when we run more exotic fuels than gasoline. In Champion, these would be L87R or L84R, for example, the suffix designating the recessed side-electrode. This is what is in MY mind when the subject is racing spark plugs. But since nobody would run this sort of plug if he didn't have to, and since you don't have to when burning gasoline, I asked a question that is probably of no interest here. :facepalm:

    Anyway, the combustion chamber shapes (and piston crown shapes) are more interesting. If you follow the car-racers' discussions of ports that impart swirl and tumble to the intake charge, you'll notice that (for them or us) the piston still has a long way to go, half a stroke, after the swirly, tumbling intake charge gets shut off. The question becomes, first, just how much is the increasingly-compressed mixture STILL swirling/tumbling as the piston approaches TDC and squashes the charge down into a tiny space? And second, how much and what kind of turbulence is imparted into the now-highly-compressed charge by the squishband? And third, can that be improved upon, and how?

    My elderly brain is failing to recall an old, obscure bit of terminology trivia. I expect you all are aware of the experimental squishband grooves of the famous/infamous Mr. Sommender Singh in India. His ideas (and remember he started as a 2-stroke motorcycle racer) are a wonderful source of speculation, though only a few engine-builders with real credibility have tried the grooves . . . with varied results, of course. Anyway, as with a lot of new ideas, somewhat similar things had been tried long before Singh's grooves. The old term that I can't remember was something like, "fire-slots" or "fire-channels" or some-such, and I first saw them in the mid-late-Sixties when OMC (Outboard Marine Corp., maker of Evinrude and Johnson outboards) came out with their first loop-scavenged engine, a 55hp triple. The heads on that motor had wide squishbands, a curious (and cast, not machined) fez-shaped combustion pocket, and two of the "fire-slots" in opposite sides of the squishband and pointed at an angle to the centrally-located sparkplug to impart a last-instant swirl. Just what Singh wants to do.

    The next iteration of the OMC triple soon followed, as the engine went in stages from 55 to 60 to 65 to 70hp. Boost ports were added (enormous boost ports, as big as the two tranfers), and the weird combustion pocket and fire-slots were replaced by a simpler, machined hemispherical combustion pocket. Maybe they learned something in the dyno cells, or maybe the new head was just simpler to turn out, with a lower scrap rate.

    You know where this is going.:yawn: Have any of you done any good tests with Singh's grooves? My first reaction on hearing about them was skeptical, but then I thought, well, we think we want that final-instant turbulence from the squish, so why sneer at somebody's new idea on enhancing that effect? I'm going to try it myself sometime next spring. I have an obsolete, homebrewed racemotor that wouldn't be competitive today, but can serve as a fine dyno-mule. This is a '73 Yamaha 125cc 56X50 motocross engine with the cooling fins mostly milled off and water-jacketed, and turned on end to make an outboard. I have a couple of extra homemade heads, and can fiddle with grooves or whatever else. I wouldn't expect anything dramatic; it just seems like a fun thing to try.

    What I'd really like to try is multi-plug heads. All the Top Fuel dragsters are using 3-plug heads, and if you fly you know that a little airplane engine always drops rpm when you switch from BOTH mags to either one singly. Again, there are undoubtedly more productive uses of one's time when searching for another couple of 2-stroke horsepower. But the weird stuff is FUN.

    (You crazed Kiwi 2-stroke tinkerers really ought to think about outboard racing, where the rules are nearly wide-open, you can convert any piston motorcycle engine, and you can use any fuel concoction you want. Yowzah!!!)

  2. #15332
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    Quote Originally Posted by seattle smitty View Post
    If you follow the car-racers' discussions of ports that impart swirl and tumble to the intake charge, you'll notice that (for them or us) the piston still has a long way to go, half a stroke, after the swirly, tumbling intake charge gets shut off. The question becomes, first, just how much is the increasingly-compressed mixture STILL swirling/tumbling as the piston approaches TDC and squashes the charge down into a tiny space? And second, how much and what kind of turbulence is imparted into the now-highly-compressed charge by the squishband? And third, can that be improved upon, and how?
    To get swirl in a four-stroke cylinder you need an asymmetrical inlet duct. But that means less flow, so you'll hardly find any swirl in a powerful four-valve engine.

    Tumble is a different matter. It comes naturally with high-flowing downdraught inlet ducts, it is augmented when the piston concentrates the tumbling charge in an ever-tighter space (like a ballerina, doing a pirouette, will spin faster when she brings her arms above her head). And in the final phase of compression the tumble is enhanced by the squish.
    Not that there is much squishband in a four-stroke; the valves occupy most of the head area, leaving relatively narrow fore-and-aft squish areas, mainly at the exhaust side. But the charge getting squeezed from between the piston and that squish area has just the right direction to enhance the tumble.

    Four-strokes need all the mixture movement they can get at that final stage of compression in order to get anything like a decent combustion; the combustion volume is shaped like a wet pancake. No wonder last year's Formula 1-engines needed an ignition advance of up to 60° at full throttle, and even more at part-throttle.
    (This year's F-1 engines don't rev, and sound like lawn mowers. Before the present rules were accepted, F-1 bos Bernie Ecclestone was warned that a low-revving six-pot turbo would not produce an attractive sound. Now he's complaining to the engine builders. What does he expect them to do? Change the laws of physics?)

  3. #15333
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    So the swirl speeds up approaching TDC, shoulda thought of that; what's that called, conservation of angular momentum or something, I'm just a dumb welder with a useless liberal arts degree. Thanks for that, Frits, although you didn't specifically address Singh and his groovy heads or multiple plugs. As to swirl in a 4-valve car engine, David Vizard did an interesting experiment in a Mitsubishi four that he built for a drag racer, with asymmetrical valve sizes specifically intended to impart swirl. Part of his intent was to keep the normal tumbling charge from tumbling right out of the exhaust ports given a wild camshaft. Google "vizard poly-quad head" to read about it.

    Well now maybe I don't see it yet. Since 2-stroke loop scavenging imparts tumble, rather than swirl, what is THAT charge doing as the piston gets up to TDC? Does the tumble velocity increase in the same manner as the spin/swirl, even though the shape of the vessel in which it is tumbling is good for swirl but not so good for tumble? The puff from the squishband (assume we have the usual centrally located combustion pocket) would NOT be in a swirl, right? So then the question again would be: would a swirl at that instant be of value, and would some grooves in the squishband, aimed NOT straight at the plug but at a small angle, impart a swirl?

  4. #15334
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    Smitty - do you remember Torquemaster spark plugs ? long reach surface gap plugs with the last of the threads machined off and used in short reach heads....Idea was to get the spark source well into the chamber.
    The reviews were a bit hit and miss as i remember - it worked well in some engines but not others. I'd assume how well they worked depended on how bad the swirl and squish worked in a particular motor.

  5. #15335
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    seattle smitty, thank you, I enjoy reading your posts. Most interseting, any pictures?

  6. #15336
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    Maybe this will help a bit

    My neighbours diary says I have boundary issues

  7. #15337
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    i have to think grooves on crankshafts dont work. if they did why wasnt there any on the rsa125 ? surely jan thiel would of used them if it was of some value





    i dont recall jan or frits recomending everyone try grooves on the combustion chamber either. leads me to believe they have little or no value. i thought a mirror polished piston top and combustion chamber was the way to go ? i been thinking of trying it.
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  8. #15338
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    Grumph, I never even heard of those plugs. Mercury outboards introduced the first surface gap plugs I know of in the late '60s along with a CD ignition. The tech rep would demonstrate the new system at the dealerships by dipping a surface gap plug into a can of grease, then showing how it would keep sparking. Yet while lots of racers immediately adopted the CD ignition (anything had to be better than Lucas magnetos!), almost no one I know used the new style plugs.

    Flettner, I'm too old and tech-challenged to post pix. I should learn. I could show you guys some fairly oddball engines.

    Yow Ling, I never knew you could fuel an engine with tomato paste. Interesting video, though I wish I could slow it down.

    Pee Wee, X2 on mirror-polishing piston tops, something motor racers have done since the Thirties as maybe the best thing you could do for a piston until ceramic coatings came along (another interesting subject). Not clear on your statement about crankshaft grooves. I'm referring to putting grooves in the squishband. Google "Sommender Singh grooves;" quite a few people think Singh is a crank, maybe that's what you referred to . . .

  9. #15339
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    Quote Originally Posted by seattle smitty View Post
    Flettner, I'm too old and tech-challenged to post pix. I should learn. I could show you guys some fairly oddball engines.
    I would love to see the oddball engines...... :D

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  10. #15340
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    Little end bearings. For the same inner diameter and width is there any reason to use either a 18mmOD or 19mmOD bearing? I'm looking at 2 similar rods but with different diameter little end eyes. Bearings are readily available for both sizes. Obviously the bearing for the 18mmOD has smaller diameter rollers than the 19mmOD

  11. #15341
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    I know there are some aftermarket rods with small L/End eyes that suit the TZ350's and the little end brg breaks up after a while, something that does not happen with the original sized L/E brg.

  12. #15342
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    Quote Originally Posted by seattle smitty View Post
    I'm just a dumb welder with a useless liberal arts degree.
    You're a free thinker. What more could anyone wish for? Yeah, more education, and that goes for all of us. No matter how much we have studied, there will come a time when we reach the borders of our knowledge and we'll have to stop calculating and start guessing. I got rather good at guessing .
    you didn't specifically address Singh and his groovy heads or multiple plugs.
    Groovy heads make me think of a rasta-band rather than a combustion chamber. All of the mixture in the combustion chamber should be concentrated in one easily-accessible (for the flame) volume. Any other shape will bring about unburned mixture and/or detonation.
    The first time I laid eyes on a grooved Singh-style head, my reaction was: "shouldn't cooling fins be on the outside of a cylinder head rather than on the inside?"

    Multiple plugs are a good thing. But just how good, depends on the shape of the chamber, on the number of millijoules your ignition system can throw at those plugs,
    and on the position of the original plug. Aprilia-experiments learned that twin plugs produced the same maximum power, revved a bit higher and required 3° less ignition advance than the original single plug. The engine also sounded a bit nicer, which makes me think of yesterday's Christopher Jacobs quote.

    Since 2-stroke loop scavenging imparts tumble, rather than swirl, what is THAT charge doing as the piston gets up to TDC? Does the tumble velocity increase in the same manner as the spin/swirl, even though the shape of the vessel in which it is tumbling is good for swirl but not so good for tumble? The puff from the squishband (assume we have the usual centrally located combustion pocket) would NOT be in a swirl, right? So then the question again would be: would a swirl at that instant be of value, and would some grooves in the squishband, aimed NOT straight at the plug but at a small angle, impart a swirl?
    Loop scavenging imparts tumble, not swirl. It would produce swirl only if the right/left symmetry of the transfer ports was faulty. And you don't want swirl;
    you don't even want tumble while the scavenging is still going on, because it would mean mixing the fresh charge with the spent gases instead of expelling those.
    The scavenging video posted above by Yow Ling, nicely shows this (assuming the CFD simulation was correct, which would mean that the scavenging of the engine in that video was far from perfect).
    Tumble is inevitable in a loop-scavenged engine, but what tumble there is, will be messed up by the squish action near TDC, which is much, much stronger.

    Tangential grooves would impart a swirl; they would also cause a pressure loss in the squish area (like grooved tires on a wet track let the water escape from between the contact areas). So no grooves for me.

  13. #15343
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    Quote Originally Posted by Frits Overmars View Post
    . So no grooves for me.
    Well, I have to try it, Frits; costs nothing but time (but then time is always the biggest hangup!!!!). I'll have a pal help me post a photo.

    I'm going to back off for a while; I've been hogging this thread for several days to where the long-time members can hardly get a word in. But let me ask one more thing:

    Looking at the references roadracers make, I take it that Aprilia's last GP engines were and are the peak of 2-stroke development so far, and that Jan Thiel is the ranking expert. Elsewhere there is a page or two of observations by Thiel, which included the number of dyno experiments he got to run every month at Aprilia. Wonderful!!

    Anyway, I'd like to know if the factory still sells parts for those 125s. Cylinders, heads, crankshaft assemblies, pistons, . . . the powerhead parts I'd need to build a couple of outboards, a 125 single and a 250 opposed-twin. Obviously I'd be fabricating the crankcase, adapting the powerhead to vertical operation, etc.. Since the factory racing operation is shut down, was/is there a production version for privateers, and does the factory still support the owners of those machines?

    I'd also like to acquire similarly high-tech parts to build a 175 opposed-twin (the 250s having gotten too fast for this old man to race himself). Half of 175 is 87.5cc. So far as I can tell, there's no roadracing class close to that displacement, but I think there is a motocross class for kids at about 80cc (true?). If there's a well-designed and currently-available cylinder with a bore in the range of 45 to 48mm, I'd like to hear about it . . .

    I really appreciate all the helpful and friendly input.

    --Smitty

  14. #15344
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    Quote Originally Posted by seattle smitty View Post
    I take it that Aprilia's last GP engines were and are the peak of 2-stroke development so far, and that Jan Thiel is the ranking expert.
    You could say that, Smitty. Jans machines won 26 FIM Constructor World Championship titles and riders using them won 300 GPs and 25 Rider World Championship titles. No one else comes close.

    I'd like to know if the factory still sells parts for those 125s....Since the factory racing operation is shut down, was/is there a production version for privateers, and does the factory still support the owners of those machines?
    I can't say; I always kept as far away from commercial things as I possibly could. And so did Jan. But a friend of ours, Thijs Hessels, produces his own parts for Aprilia racers (with a little input from Jan) and his cylinders are as good as the works RSA cylinders (hesselsfijnmechanica@versatel.nl).
    Another option is to take a look at the various people who build 250 cc tandem-twin engines for superkarts: DEA, FPE, PVP, BRC, etc.
    They all based their products on the Aprilia RSA.

    I think there is a motocross class for kids at about 80cc (true?). If there's a well-designed and currently-available cylinder with a bore in the range of 45 to 48mm, I'd like to hear about it
    KTM builds motocross machines with 65 cc (bore x stroke = 45 x 40,8 mm) and 85 cc (bore x stroke 47 x 48,95 mm). Those cylinders are not bad.

  15. #15345
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    Smitty, all the Japanese manufacturers make 85cc motoX bikes with oversize pistons available up to +2mm, some of the cylinders are Cast iron bores some Nicasil, our rules prevent us from using them in Buckets, The 85 cc engines are around 22hp
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