mrx

Hallo,

i asked myself if the piston design have any effect on the point when detonation occures?

if yes, what design is good and what is bad?

is there someone who has real technical backround and can answer on this question?

Thanks
Malte.

rhd

yes...that's about 50% of it

Ri5e

The higher the compression, the higher the chance of detonation

Also, pistons with a lot of jagged edges will create hot spots that can cause pre-ignition which causes detonation. However, most manufacturers will "buff out" the edges so that they are smooth.

beepy

The ideal piston is perfectly flat. If you could get away with flattops and good compression then go for it.

earl

I asked CP that question once and they said if your air/fuel mixture is correct, you can put spikes on top of the piston and you won't detonate. You only get hot spots when running too lean in the first place.

system60

AFAIK , unless you have alot of jagged spots on the piston to create hot spots, it doesnt matter. Id figure its more in the combustion chamber. coming from VWs the old 8v cant take as much timing as the more modern 20v head that seems to be able to eat up timing in comparison

blundar

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TurboSmart &raquo;</TD></TR><TR><TD CLASS="quote">The higher the compression, the higher the chance of detonation</TD></TR></TABLE>
Not necessarily. The picture is considerably more complicated than this. Things like quench+squish can play a huge role, particularly with higher R/S engines where the pistons dwells at TDC for longer periods of time. Particularly with a favorable head design (GSR, Y8 for instance) you can really do wonders.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TurboSmart &raquo;</TD></TR><TR><TD CLASS="quote">Also, pistons with a lot of jagged edges will create hot spots that can cause pre-ignition which causes detonation. However, most manufacturers will "buff out" the edges so that they are smooth.</TD></TR></TABLE>
I've yet to see a piston that came out of the box with all the edges "buffed out" to my satisfaction. In addition to taking fine-grit to any edges (including valve relief cuts) I'd also highly recommend getting the piston tops + skirts ceramic coated to improve their ability to reject heat.

Remember that the combustion chamber in the head is only half of the true combustion space - the top of the piston is the other half. The design of your piston is effectively half of the design of your combustion chamber.

This is a huge topic. I will probably get flamed for saying this, but Endyn has some fairly decent articles on piston/combustion chamber design that are definately worth checking out. Also, googling for "quench" with "piston" and some other juicy terms can drag up the occaisonal interesting tidbit.

bbarbulo

it's really the shape of the combustion chamber that affect detonation, and since the piston face is part of the combustion chamber, I'd have to say hell YEAH!

As for what is best... again, the piston and the shape of the head CC work together to promote even distribution of the intake charge, and you want a nice even flame front with no lean/hot spots in your mix.

m R g S r

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blundar &raquo;</TD></TR><TR><TD CLASS="quote">
I will probably get flamed for saying this, but Endyn has some fairly decent articles on piston/combustion chamber design that are definately worth checking out. </TD></TR></TABLE>

why?

blundar

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by m R g S r &raquo;</TD></TR><TR><TD CLASS="quote">

why?</TD></TR></TABLE>
To make a long story short (and I might even get flamed for this summary) Larry is a dreamer and tinkerer much more than he is a businessman. Additionally, he seems to have a bad habit of shooting himself in the foot with ... somewhat inflated claims. Many people (as I once did) totally disregard what the man has to say because of the public persona his shop has developed.

I feel that regardless of how the man has carried himself in public, regardless of "how many HP _____ motor built by Larry" made, the man has a lot of very solid ideas to offer the racing community. Execution hasn't always been great, advertising/press has often been horrible but the potential is there. liveforphysics has done some very thorough scientific studies towards his degree exploring some of the piston / combustion chamber design techniques advocated by Larry with great success. Many of the OEMs are slowly catching on as the shift from the massive chamber (Hemi/D16A6/ZC/B16A1/D16Z6) designs to more closed-chamber quench heavy designs (B18C1, Y8).