ESE's works engine tuner

[speedpro]

What I am suggesting is slightly more elegant, in that the next step to what we really want cooled the most is the end gases trapped between the piston and the insert.

An insert within an insert would seem possible at 1st thought, with 2 seperate cooling circuits. O-rings would handle sealing and the boundary between inserts would create a step in temperature between the inserts. One insert being the squish and the other the actual combustion chamber bowl. Have to be careful with hot edges in the combustion chamber.

Re the damaged motor, I pulled it down last night and detonation was the problem. The piston has a slightly furry patch in the centre and on the exhaust side in the squish area there were 2 chips knocked off the crown and other fuzzy sort of damage. Time to take it out to the next oversize, 52.15 from 52.1 and only because I got the pistons. the bore is good(ish). Love those kart pistons and their .05 oversizes.

[ken seeber]

Smitty,
Have been reading the latest round on cooling discussion, but with the mind focussing on more pressing matters, haven’t had the opportunity to comment of late.
My take on cooling a 2 stroke is that, as Frits says, you can never over cool a 2 stroke. This is a very general statement, generally applying to the overall engine. Cold air passing thru equals:
• Higher charge density – more power
• Cooler temps mean better lubrication control and durability(less oil breakdown/carburizing)
• Cooler temps mean less opportunity for detonation
You are fortunate with boats in that you have the world’s biggest radiator at your disposal, with typically a 15 – 20 deg C inlet flow temp, compared to bikes/karts where the ambient temp can vary from whatever in the northern hemisphere to over 40 in Oz. From this potentially high ambient temp we need to cool the coolant down to as low as possible maybe as a guess, even with a huge radiator, that this might have delta T of 10 deg over ambient. Passing through the engine, I seem to remember that a fairly normal increase was around 5 deg, this being obviously dependent on the flow rate. The higher the flow rate the better the actual heat transfer rate, giving a smaller overall temp differential across the engine. If the 5 deg is in fact the case in current racing 2 strokes (will bow to Frits and Wob on these matters), then the need for a separate circuit is hard to justify, but who knows…I don’t. The downside to higher flow rates is the power required to drive the pump and its heat input into the cooling system (previously discussed).
However what Wob is saying, I am sure, that overall cooling is good for all the obvious reasons, HOWEVER in certain areas there are specific needs for power and engine durability. Specifically:
• We want the spark plug to remain as cool as possible
• We want the two surfaces (head outer circumference and piston crown edge) that form the squish zone to be as cool as possible to avoid detonation
• We want the combustion zone to be as warm as possible tor maximum Carnot cycle efficiency, consistent of course with detonation and even pre-ignition control.
There have been some attempts at detonation control (other than the more subtle methods that are being currently employed), one of these being Warren Willing’s Yamaha sprung loaded cyl head combustion chamber that after a certain cylinder pressure was attained, the whole insert would shift outwards, allowing the pressure to drop. Dunno if it was ever successfully used though.
Back to combustion chambers. I think the ideal shape for a combustion shape is a sphere, which offers a minimum surface area to volume ratio, thereby minimizing heat transfer, allowing maximum combustion temps and efficiency. By employing squish zones, this allows a more compact combustion chamber shape. Not perfect, but clearly the way to go. And as Wob has been saying, the toroidal shape within the head is desirable as (I think) it places the spark plug gap towards the centre of the zone (obviously more so in the case of the flat top piston) so the flame kernel can radially progress. My understanding anyway.
If you want to see a shit combustion chamber, have a look at this: https://www.youtube.com/watch?v=0SiRqmo5Onc It can be clearly seen at the 3 minute stage.
In recognition of this, a direct fuel injection system was developed that, under the generic terminology of the day, DISC (direct injection stratified charge) which allowed the fuel (and a small quantity of injection air) to be injected late in) the compression cycle such that no fuel entered the acres of squish area. In that case, we were chasing fuel consumption and low unburnt HC emissions.
As a digression, this fuel injection system was very successful, particularly so when applied to a 2 stroke engine. (both crankcase or externally scavenged). The system is still being commercially manufactured today with applications such as marine (Mercury Optimax) to small drone engines (spark ignited running on jet fuel).
Personally I wish that some of the dumb arse controlling bodies, particularly in karting (which in my understanding is the largest (numerical) arena for competition 2 strokes) where they stick to archaic/ill considered rules (possibly for pecuniary reasons) and don’t allow any significant technical advancement opportunities, would use their imagination.
That’s what is great about this bucket thing. Lots of regulation freedom and cultural freedom, allowing guys like Neil and TZ350 and many others experiment, hopefully leading to the advancement of 2 strokes and their rightful and justifiable place in the future.
My thoughts anyway.

[Larry Wiechman]

Seems that we've been pumping the coolant the wrong direction, all these years. Wouldn't it be better to have the biggest temperature delta in the head instead of the cylinder?

[Yow Ling]

What I am suggesting is slightly more elegant, in that the next step to what we really want cooled the most is the end gases trapped between the piston and the insert.

Could always put a mask , like when you etch a pcb, over the combustion chamber part of the dome on the water side. Use a material like an epoxy paint that has a known thermal resistance. Leave the squish bit unpainted and allow the water up to the plug threads

[wobbly]

There are two issues in the cylinder that need the most attention from the coolest water available.
Over the transfer duct outer walls, and the Ex duct outer walls.
The first as this keeps the inducted charge as cool as possible, the second is to keep the trapped slug of fresh ( ish ) fuel air in the Ex duct
also as cool as possible.
The slug gets stuffed back past the closing piston ,thus this contributes to the combustion process - and if overheated it creates deto very quickly.
Wrap your header with glass insulation tape - and quickly find out what not to be doing.
We have a trade off situation in the cylinder/head interface.
As Frits alludes to we dont want a "hot " head contributing heat to the cool charge being compressed prior to ignition, but on the other side of this coin we dont want
cold alloy pulling heat out of the ignited mixture.
As DEA etal have found the tradeoff currently works in the favour of the carpet bombing approach of cooling the hell out of everything in the head.
But as I have found dozens of times if you ceramic coat the chamber only, power goes up.
When you ceramic coat, two things happen.The coolant temp drops, always a good thing, and this cooler water in the head then possibly has a chance to do more good by
dropping the end gas temps, thus helping to keep deto at bay.
Jan found a very simple way of keeping the plug cool, you guys wanting to tune to the edge of available power need to think of your own solution to effectively
cooling the squishband, in a better way than the current carpet bomb approach.

[seattle smitty]

(Quote=Wobbly) ". . . you guys wanting to tune to the edge of available power need to think of your own solution to effectively cooling the squishband, in a better way than the current carpet bomb approach." (end quote)


EASY, when the answer is handed to us, gift-wrapped! Dang, Wobbly, if you were in Japan they'd declare you a "Living National Treasure," and put a giant medal on your chest, with crossed bounce-pipes on a backqround of chrysanthemums and castor beans.

This is an especially easy thing to do in an outboard. You don't particularly want water leaks to the outside, just as a matter of pride in workmanship, but if you do have odd water-jacket seeps past home-designed gasketing and o-ringing, it doesn't matter! Your coolant all goes over the side anyway after it has done its job (flow through the engine is controlled by restricting water-out). An extremely simple modification to the head design I carved from billet long ago will do exactly what you advocate. Nothing in the rules says you have to put all the coolant into the engine at a single point and trust it to flow around just as you hope; you can make a water manifold that puts the water in at a number of points. This manifold can have big lines going some places and small lines going elsewhere. In outboards, we frequently let the water OUT of the engine at multiple points as well.

(I just wish my personal road to enlightenment didn't have to be paved with my endless long-winded and doofus questions in between the "AHA!!" moments!!)

[TZ350]

.... what is great about this bucket thing. Lots of regulation freedom and cultural freedom to experiment ....

Yes we are very lucky, and the class structure makes it affordable too and competitive enough to keep skilled riders happy, I love it.

[Frits Overmars]

I shouldn't ignore that you are advising a readership comprised overwhelmingly of motorcycle racers, and probably some kart racers; for both of them, the coolant enters their engines already twice as hot as the water entering a racing outboard engine.

Smitty, basing your opinion about my experience on the prevailing type of readership here may not be the way to go.
As long as 30 years ago (yes, I'm an old sod) you would not find any form of radiator on Jan Thiel's Garelli test bench. There was a hose from the cold water tap to the engine and a hose from the engine to the sewer. And Jan was not afraid to measure a stone cold engine at full throttle. It made him realize were the power is, and how important cooling is.

I am, as everyone should be, very wary of contradicting what Frits has to say

Thanks for the flowers Wob. I hope everyone here realizes that we all owe you the same courtesy.

in this case he is citing the result gained from the DEA head as being exactly what he found in practice works best. That is, cool the hell out of everything - the carpet bombing approach.

There's two ways to look at this.
A: You can't argue with measured results, provided that these results include all the variables that played a role during the measuring.
B: Those results will not prove that they are the optimum. There may always be better, or as you put it, more elegant ways to advance. You made me curious...

what we really want cooled the most is the end gases trapped between the piston and the insert.

That's where detonation occurs, so your desire is logical. But around here a quote from yours truly has become well-known:
"Squish it till the doctor comes; try to get your dynamic squish gap down to zero. Mixture that isn't there anymore, won't detonate".

There are two issues in the cylinder that need the most attention from the coolest water available. Over the transfer duct outer walls, and the Ex duct outer walls.

Don't forget the transfers' inner walls. That brought another HP or so for the RSA. Yes, I know, that will require some casting skills. Or the Selective Laser Melting that I used for the FOS cylinder.

[husaberg]

Yamaha during the sixties found a correctly fuelled air cooled engine HP fell from 30 cold to 23 HP when tested hot.
Where as a over rich mixtured one began with only 27 yet when hot still made 25hp.
Of course the figures were not as good as a water cooled ones lesser power fade.

Re the damaged motor, I pulled it down last night and detonation was the problem. The piston has a slightly furry patch in the centre and on the exhaust side in the squish area there were 2 chips knocked off the crown and other fuzzy sort of damage. Time to take it out to the next oversize, 52.15 from 52.1 and only because I got the pistons. the bore is good(ish). Love those kart pistons and their .05 oversizes.

I don't understand the furry bits in the middle? Wouldn't damage or erosion their not also suggest pre ignition?

[Martin1981]

From time to time one just has to say thank you to wob frits and all the other 2 stroke builders and tuners for that awesome thread. Wayne and Frits are sharing their lifework with us. one can not appreciate that enough. if only we could meet all together in New Zealand someday and talk about that simple looking but so complex and complicated 2 stroke engines (and and eating bratwurst). kicked ass by politicans unfortunately for to me no obvious reason. fortunately there are some people left on earth paying the 2 stroke the attention it deserves. thanks Jan Thiel, Wayne and Frits and all the others!!!!!!!!


Mentioning Jan Thiel.... Frits, one remarkable issue, at least to me.... it seems that Jan realized just from the Beginning that the rotary inlet is the best for power. there are not many pictures showing Jan with piston port or reed valve engine. maybe a stupid question but is that the only reason (power) that he so to speak started straight off with the rotary inlet system or are there other reasons that makes him prefering it?

[Frits Overmars]

it seems that Jan realized just from the Beginning that the rotary inlet is the best for power. there are not many pictures showing Jan with piston port or reed valve engine. maybe a stupid question but is that the only reason (power) that he so to speak started straight off with the rotary inlet system or are there other reasons that makes him prefering it?

Jan should be answering this really, but I'll give it a try. I assume he started with a rotary because everybody in GPs was using that when Jan built his first engine.
For his own constructions he always stuck to rotaries, with one exception: the reed valve Rumi. It produced 46 hp on the test bench in a season where the world title was won with 42 hp, so our prospects were bright. Sadly this could not be said of management...
Jan made a direct comparison at Derbi where he developed the RSA while Lorenzo's GP-winning reed valve Derbi was still around. Jan worked on both engines, extracting 49 hp from the reed valver before dropping it in favour of the rotary RSA that produced 10% more power with the same cylinder.
The rotary engine has other advantages over the reed valver: setting the carburation is much less fussy. But the power difference is the main attraction.

[seattle smitty]

[QUOTE=Frits Overmars] As long as 30 years ago (yes, I'm an old sod) you would not find any form of radiator on Jan Thiel's Garelli test bench. There was a hose from the cold water tap to the engine and a hose from the engine to the sewer. And Jan was not afraid to measure a stone cold engine at full throttle. It made him realize were the power is, and how important cooling is. (QUOTE]

Frits, one reason I keep asking, even after someone who knows more than I do makes an assertion that to his mind is clear and final, is that if we can get him to keep amplifying his experience we might see the WHY of his conclusions. And right or wrong, we might then decide it doesn't quite apply to our individual situations.

For instance, if I just decide, "Well, okay, the man says 'the colder the better.'" I could ram-feed LOTS of water into an outboard at higher pressure than city-water faucets, using huge hoses and manifolding to put it into the engine at numerous locations and with lots of drains at the other end, and I could build a head that has internal fins giving ENORMOUS surface area for this river of water to flow over. Going on, you tell us Jan "was not afraid to measure a stone-cold engine at full throttle." What is a duffer like me supposed to make of that one if I don't ask about it, seeing that many other two-stroke owners have skidded pistons that weren't yet expanded and sealing well (commonly seen as a "four-point seizure")?? Which of these incompatible "findings" applies best to MY engine? Should I massively cool my engine and start buying boxes of semi-finished pistons that I can turn with a lot less taper and clearance than standard? This kind of thing is why I hope to learn what's behind anybody's flat assertion of what is best practice.

There is not a pfennig of prize money in the racing 98% of us know; a boat is a hole in the water into which you pour money (there must be a similar saying for bikers and karters), so we have to be a little cautious. So as another "for instance," when Wobbly says cool the squishband, and you say, no, squish harder, I'm inclined toward cooling it because I can't be whacking too many pistons trying to find the sweet-spot, a dimension which will exactly apply only to THAT engine. As an eighth-grade teacher once told me, "Sometimes discretion is the better part of valor."

(EDIT) You're old, okay, . . . but an "old SOD"??? Frits, that's MORE than I need to know!!

[Frits Overmars]

Frits, one reason I keep asking, even after someone who knows more than I do makes an assertion that to his mind is clear and final, is that if we can get him to keep amplifying his experience we might see the WHY of his conclusions. And right or wrong, we might then decide it doesn't quite apply to our individual situations.

You know the type of kid who drives his parents crazy because he keeps asking 'Why?'
No, I'm not going to say what you fear right now. I'll just say that I was that kind of kid myself, and still am, so I can understand what you mean.

Which of these incompatible "findings" applies best to MY engine?

That works two-way only: I can only answer your questions if I know your engine inside-out. But that would be a day job, and I've already got one.

Wobbly says cool the squishband, and you say, no, squish harder!

I never said no to cooling the squish band. And I said 'squish hard', not 'harder' because I do not know how hard he is squishing right now.

[Muciek]

Finished Webco reproduction heads for RD350/400 with Wobbly designed combustion chambers

[wobbly]

There is a 250 version as well, jfyi,and luckily for me the first back to back dyno run gave +6Hp.