piston type/flame travel

[spork]

Hey, someone help me out. I've been talking to my machine shop about my currect engine build-up (l28et) I'm keeping compression low (in the 7.5-8.0:1 range and running a 2mm hks gasket. My question is about piston shape versus cylinder efficiency and which one promotes the best flame travel for my setup. I'll be running the P-90 head if that matters. I'll be the first to admit that I know little to nothing about flame travel etc other than the concept of what happens. The deal is I can get forged flat top pistons for $70 cheaper than dished pistons, but I don't want to compromise any engine performance just for $70. Some one please help, I don't have the education/experience in this area to make the correct decision. Thanks,

 

James

[spork]

I can't get my pm to go through to you, so heres the info. They're ross pistons and priced at $664.00 with pins for the dished piston. $70 less for flat tops. I checked with venolia, JE and and a couple other companys and they all have a much longer lead time than Ross does. So that is also I slight concern for me, but if I go with flat tops, they'd be the best priced and quickest to get.

[TimZ]

Since the P90 is a closed chamber head, an ordinary dished piston will negate any advantages that you might have gained from the closed chamber's "squish" area. If you can achieve the CR that you want with flattops, that would be the preferred route. Note that the flattops would need to have zero (or near zero) deck height - adding volume with negative deck height is the same as a dished piston.

 

If you need more combustion chamber volume than you can get with flattops, the dish in the piston needs to have the same shape as the combustion chamber in the head, so that you will maintain the proper squish.