Can anyone explain how the design of a piston effects the combustion process. I was reading the "how to build a reliable lsvtec/b20vtec" and saw this.

Then this reply,
Just wanted some insite on piston design. Which design is more efficient?

 

It's a generally accepted principle that a flatter top piston is better for flame travel, tends to be more resistant to detonation, you can run a little more timing all while using pump gas.

If built and tuned well, it may be possible to make more power on a domed piston, I wouldn't know as I haven't tested or experienced it myself. If I was building a motor, I would personally stay away from the CTR pistons but ultimately the choice will be yours.

 

check out cbr, gsxr, crf, yfz pistons. any of the pistons in rockets or 4stroke MX bikes. all engines making exceptional power per cid

here is some F1 stuff. check out the piston with the signatures on the top.
https://www.team-bhp.com/forum/techn...gine-pics.html


make your own conclusion about domes.

 

Those pistons look like they're probably mirror's of their respective combustion chambers. they aren't the ridiculous / \ shaped domes. There's surely a point where combustion effeciency loses to compression or you wouldn't see them out there. I guess it would be easy/ideal if a given motor made adequate compression with flat top pistons.

 

the problem arises then the chamber is too large for the desired compression. the easiest thing to do is make the piston to take up the space.

it's all a packaging deal on the engines we are dealing with. on production stuff the intake manifold cant stick up out of the hood and the engine cant be lowered any more to keep the IM under the hood so the ports are shallow in the head. then the valve gets angled more and the chamber gets more of a peak in it.

 

This is exactly what I was thinking. I had a VR6 GTI before my integra and was looking into rebuilding the motor. The pistons on that motor were flat, but this was reletive to the 12v vr6 head design. So ideally the best piston would be a flat top piston that can provide high compression. This is not achievable considering the design of the Honda head?

 

Those flat spots that seem to mirror the combustion chamber are called quench zones. They force the fuel mixture toward the spark plug creating a more complete burn. In doing this they also keep those flat areas cooler and reduce detonation in a high compression chamber. Honestly I never understood the exaggerated /\ on most of the B series HC pistons. But now I see that it is because of poor OEM combustion chamber design.

The aftermarket only feeds the demand for people wanting higher compression engines. In order to do this they create drastic dome pistons to fill the large combustion chambers. It's much easier to do that than it would be to change the geometry of the combustion chamber.

 

WELL PUT. Funny how engines like F22A, F22B SOHC and F23 can make nice compression with flat top pistons, yet weren't intended for performance applications.

 

no, but they were intended to be efficient, hence the design.

 

Sorry, I could've worded it better. My point is that you can achieve 11-12:1 compression with flat top pistons in the Accord engines (possibly others as well), which is ideal. Why are the higher performance motors designed to use heavy domed slugs? Isn't that a design flaw?

 

Originally Posted by ALL M0T0R
Your so outta your ball park its unreal.
They aren't in anyway identical to p30's. P30's are used as a good solution to people wanna bump the compression up, and have a good flame and piston weight

CTR pistons are called slugs for a reason. They are the heaviest piston for b series.. and the dome is entirely too fat and big, it spreads the flame too thin and doesn't allow for the correct combustion process.. other pistons come to a point, you'll notice on ctr's at the top of the dome is almost flat for 3/8ths of a inch which spreads the flame too thin..


ctrs are ****en garbage. They belong in nothing but a b16.

Can someone explain to me what this guy is trying to say for clarification. So a flat piston is more efficient, but he says the ctr piston is to flat "which spreads the flame to thin".

 

ctr piston has too wide/flat of a peak is what he was saying I believe. A flat-top piston would have no peak whatsoever.

 

Correct. Ya he's more or less saying that the height of the dome on those pistons act like a wall, disrupting the flame travel across the top of the piston.

Most higher performance motors don't use "heavy domed slugs", it's only the B16b that uses them. It's not so much a design flaw as it's a design "compromise". In those situations a part is sometimes selected that will do the job but not necessarily in the best possible mannor to achieve a certain goal in a certain way. It's possible that Honda wanted a simple solution to achieving a certain compression ratio in the b16b without having to change anything else like rod length or stroke etc. In that sense, many aftermarket companies do the same thing by designing large domed pistons to gain a certain level of compression to perhaps run a certain type of cam or fuel. It is better to redesign the combustion chamber, alter rod length or stroke and come up with a more efficient design but this obviously costs more money and isn't always possible. So the domed piston is the cheapest "compromise".

 

Not a design flaw, but rather a compromise.

A domed head allows for larger valves, with allows better high RPM breathing, which is where performance oriented Honda engines make their power, which is why performance Honda engines have domed heads and pistons.

 

with the design of the head you can pretty much stuff the chamber full of piston and get away with it. other engines, not so much.

the theory is sound, but in practice it doesn't make much difference.

I have a mahle Toyota F1 piston.. im not sure of the CR of those engines but the piston does not have a dome per say, but you can tell from the design of the piston that they basically fill the chamber with the piston. the valves are early parallel which further allows for this design.

the old "dome hurts efficiency" thing holds very true for engines with crappy 2 valve heads, on a good 4 valve chamber its not really that big of an issue.

 

Ideally you want a relatively flat dome and piston combination, but modern day packaging and other factors sometimes require a deeper dome.

 

Thank you sir, makes sense!