ESE's works engine tuner

[seattle smitty]

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.

NO, no, I posed the question rhetorically, exactly to point out that to make my own decisions for my own machinery, I want to get some sort of understanding of what went into your decisions . . . . much as I might want you to retire, move to Seattle, and become my personal private outboard engine-builder.

But I WOULD like to know why Jan Thiel could go WFO with an un-warmed-up engine, where our engines, given that treatment, will likely go RRRRIIIIIINNNNNGGGG-bleeeeeugh-squeak . . . AND whether when you/he found that very-well-cooled engines worked better, did you alter the taper and fit-up of your pistons??

[F5 Dave]

So the reduction of squish.

All figures made up and assuming a road based crank which may not be as stiff,

lets say a static squish of 0.7mm

start the engine & it becomes 0.3
9000 it goes 0.2
12000 0.1

does that sound reasonable order of magnitude?

So you will have more mixture trapped at 9000 than 12000.


It can be a tricky phenomena. Just Sunday I was getting flashes on my Knockgauge at the end of the straight, yet up the hill in 6th right through to over-revving it was fine. You'd think that would put more load on.

[Yow Ling]

But I WOULD like to know why Jan Thiel could go WFO with an un-warmed-up engine, where our engines, given that treatment, will likely go RRRRIIIIIINNNNNGGGG-bleeeeeugh-squeak . . . AND whether when you/he found that very-well-cooled engines worked better, did you alter the taper and fit-up of your pistons??

Possibly because the piston and the bore had similar expansion rates as they warmed up, unlike a CI sleeve which will expand much slower than the piston heats up

[wobbly]

The Aprilia setup with 0.7 squish I believe would just clip at the absolute overev margin of 14500
Now I have the squish cooling organised in KZ2 I can run down at 0.9 ( from 1.3 min ) and it just clips at 15200.
The 66 bore Banshee/RZ based race engine with 58 stroke set at 1mm will clip at 12200.
A TM125 MX engine for open karts would clip at 13200 with 0.6mm
A CR250 road racer set at 0.9 will clip at 11400.
That gives you some idea of the state of play from real experience.

The big open class Jetski World Champ engines I used to build needed an absolute minimum of .15mm = 0.006" clearance
on 78 to 92 bore when running 40*C out of the case and 60*C out of the head.
On the dyno the power would fade at the end of a 30 second pull if the case went over 40* - much under that and we would certainly squeek a piston.
We used restrictor jets on the individual 6 outlet points to regulate the local temps.

[Frits Overmars]

I WOULD like to know why Jan Thiel could go WFO with an un-warmed-up engine, where our engines, given that treatment, will likely go RRRRIIIIIINNNNNGGGG-bleeeeeugh-squeak . . . AND whether when you/he found that very-well-cooled engines worked better, did you alter the taper and fit-up of your pistons??

Possibly because the piston and the bore had similar expansion rates as they warmed up, unlike a CI sleeve which will expand much slower than the piston heats up

Right, and it's self-amplifying too: the piston will heat up much faster in a sleeve because the sleeve itself won't conduct sufficient heat to the cylinder body.
I don't hate sleeves without a reason.
Of course the piston shape (an oval, conical barrel) was adjusted on the basis of the wear pattern. But that's nothing new; you've got to do that with every engine.

[F5 Dave]

The Aprilia setup with 0.7 squish I believe would just clip at the absolute overev margin of 14500
Now I have the squish cooling organised in KZ2 I can run down at 0.9 ( from 1.3 min ) and it just clips at 15200.
The 66 bore Banshee/RZ based race engine with 58 stroke set at 1mm will clip at 12200.
A TM125 MX engine for open karts would clip at 13200 with 0.6mm
A CR250 road racer set at 0.9 will clip at 11400.
That gives you some idea of the state of play from real experience.

.. .

Thanks. What it doesn't tell me, if I really needed to know other than idle curiosity, is what the dynamic squish is at lowest usable revs. The numbers seem to indicate that heavy pistons and lots of revs continue to stretch but I'd imagine that bearing clearance would take up early on. In absence of measuring equipment one would need to build an engine with say 0.5 and rev it to a low figure and check. Just curious.

[kel]

Question for Wobbly, do you know the name of the tape, and where I might purchase this tape, as used for masking the squish area of piston pre ceramic coating (the stuff that was used by BSL before sending pistons to HPC). Thanks

[wobbly]

As far as I know HPC made a circular mask that simply sat on the piston crown, and the ceramic was sprayed on like a paint.
Then it was heat cured.
Because there was a definitive line around the squish edge where the piston became flat, it was easy to align the mask.

[husaberg]

Thanks. What it doesn't tell me, if I really needed to know other than idle curiosity, is what the dynamic squish is at lowest usable revs. The numbers seem to indicate that heavy pistons and lots of revs continue to stretch but I'd imagine that bearing clearance would take up early on. In absence of measuring equipment one would need to build an engine with say 0.5 and rev it to a low figure and check. Just curious.

I seen something with a v8 block ran headless and filmed slow mo, The rod stretched a lot. I have pulled that figure out of my ass.
Anyway force equals mass x accerleration.

But here is the F1 stuff

Cosworth's 2005 V10 was the TJ model, which had its max RPM at 19,000 rpm. With next year model CA, Cosworth took the uncompromising approach of targeting 20,000 rpm from the outset. This was the first time it had produced such a high-speed V8. At 20,000 rpm the CA's maximum piston acceleration was 10,616 g while the load imparted on each crankpin by the associated piston and con rod reached a very substantial 5937 kg at that unprecedented speed. To put that into context, an anti-ballistic missile attains a g-force of only 100 g while 5937 kg is approximately two and a half times the weight of a Rolls Royce Wraith! Cosworth, to counteract high friction that can counteract horsepower gain, applyed a Diamond-Like Carbon (DLC) coating to the piston skirts.

Revving to 18,000 RPM, a modern Formula One engine will consume a phenomenal 450 liters of air every second, with race fuel consumption typically around the 65 l/100 Km. Revving at such massive speeds equates to an accelerative force on the pistons of nearly 9000 times gravity (9000 G).


Of course, the biggest challenge has been holding everything together as reciprocating and rotating parts are worked ever faster, and generate increasingly fierce loadings. Even at "only" 12,000rpm there are seven tons of load going up a con rod, which responds by growing longer, then 12 tons going down it, which unavoidably shortens it somewhat! F1 piston travels only about 40 millimeters and acceleration from 0 to 100kmh has been measured at 0.0005 seconds. The bore is roughly 98 millimeters (called supersquare bore (wider than higher)).
The engines produce over 100,000 BTU per minute (1,750 kW) of heat that
must be dumped, usually to the atmosphere via radiators and the exhaust, which can reach temperatures over 1,000 degrees Celsius. Nonetheless a Formula One engine is over 20% more efficient at turning fuel into power than even the most economical small car. Unsurprisingly, engine-related failures remain one of the most common causes of retirements in races. The engine oil capacity is about 3 litre or so. This is because of the dry sump system.

Calculating inertia force
http://www.wallaceracing.com/Calcula...-of-Piston.php

[rodg]

Long time listener (lurker?) first time caller....

Thanks to the lads at the house of speed I finally got my AM6 (50mm malossi mhr replica barrel) powered TZ 80 onto the dyno tonight. Unlike pretty much everyone else on this thread I'm a strict amateur when it comes to building motors and my first up dyno run confirms such! I was pretty confident I had built up a tidy little motor that would deliver 15+ HP pre-tuning (it feels faster than my 14-ish HP FXR).

First dyno chart below (red) came as a bit of a shock - 10HP!. A bit of fiddling with the ignition (PVL Go Kart analog) and leaning up the main pushed us out to 15HP pretty easily but as you can see the graph is horrid.

Thanks to the generosity and experience of the lads we'll spend a couple more nights on it and i'll keep you posted.....

[adegnes]

Maybe start accounting for rod compression when aligning the piston and transfer port floors @btdc, just like you account for stretch when setting the squish?
I've actually done just that, piston dome is 0.3mm above transfer port floors, I don't know exactly how much rod compression there is, just picked a number. (39.1x40 stroke/bore)

[chrisc]

Thanks to the generosity and experience of the lads we'll spend a couple more nights on it and i'll keep you posted.....

Ah Jesus, why would they do such a thing, you're fast enough on that thing already!

[F5 Dave]

Maybe start accounting for rod compression when aligning the piston and transfer port floors @btdc, just like you account for stretch when setting the squish?
I've actually done just that, piston dome is 0.3mm above transfer port floors, I don't know exactly how much rod compression there is, just picked a number. (39.1x40 stroke/bore)

Hadn't even Thought of that but it makes sense,. . . though empirically the slight overhang might be worth it for a teensy longer flow cooling that piston.

[Frits Overmars]

What it doesn't tell me, is what the dynamic squish is at lowest usable revs.

I can't for the life of me think of a reason why you would want to know that. What can you use this knowledge for? Please enlighten me.

In absence of measuring equipment one would need to build an engine with say 0.5 and rev it to a low figure and check.

We have measuring equipment. You may remember the story where mechanical contact between piston and head fooled a detonation sensor into shouting 'deto!'
So minimize the chance of real detonation by retarding the ignition timing and run your engine until the deto sensor shouts. Because of this late ignition the pressure rise above the piston will be later than usual, so the force slowing the piston down will be less than usual. Then if you advance the ignition to its previous value, the touch-rpm that you just established will be safe at WOT. But close the throttle and the pressure will drop, increasing the piston overshoot.
This was the reason that the 100 cc direct-drive kart engines of yesteryear, that could be revved past 20.000 rpm, should be braked down to more civilized revs before you could close the throttle. If you did it the other way round, chances were that the con rod would self-destruct, taking the rest of the engine with it.

[F5 Dave]

OK that makes sense I think (slowly).

My thought process was that if you can help stave off deto by reducing squish to as little as possible, this is only most effective approaching peak revs. So at the bottom of the useable power there is more trapped mixture. But I wasn't sure how much more.

I also thought of the sliding head but it does seem complex for what might be minor gain. That said perhaps if you could decrease deto you might be able to crank up advance at 9000.