ok there are many ways to achieve a target compression ratio by changing head gasket thickness, deck height, pistons, head chamber size etc. my question is, all other variable the same, which is more important: a tighter quench? or using a flattop piston instead of a dished one? i know flattops are desireable from a swirl perspective, but so is a tight quench. which has more bearing on optimal combustion?

 

with my limited knowledge and research into this i'd run a dished piston over a flat top. guess before i really did it i'd do some more reading. for the record the last engine i built had domed pistons.

 

I believe current theory is that dished pistons will be the best. Because the piston has a larger surface area more energy is transfered to it. Compared to a larger, open chamber design that have a large surface area. As dished pistons shouldn't harm detonation resistance as much as messing up the quench.

 

I don't have too much experience with different pistons, but I have noticed that higher performance engines all use flattop pistons. LS1, LT1, old skool LT-1, and all of the hi-pro 327 vette motors. I think it has something to do with the breathing characteristics of a high rpm NA motor. For blower of nitrous or turbo a dished with a thight quench might be better for the burn. I would think a flat top would fill the cylinder better on the intake stroke.

Flattops are the way to go unless you are building a specific low octane or boosted motor. And it also dependds on the dish shape. I hear D-shaped pistons are good for a low compression motor. All I know is, the stock dish shape with valve reliefs and chamfered edge is possibly the worst piston GM ever put out.

 

Its very interesting to read how this debate keeps changing.
What remains constant is the fact that the factory style pistons dished, then dished some more with valve releifs arent as effecient in combustion as a smoother surface.

 

A reverse dome (aka D-cup) piston can still retain the quench characteristics of a flattop.

Your limited knowledge?

 

It really depends what you are going to run for heads. and how many cc's they are also cam?

 

LPE cnc ported aluminum L98 63cc heads and a zz-409 cam (226/226@.050, .560/.560 lift w/ 1.6:1, 112 lsa) in a forged 383 stroker for street use. target c/r will be in the 10.5 - 10.8 to 1 range

 

Nuh uh... those engines (The Hi-Perf 327s and 350s) all used domed pistons, as did the Z/28 engine (302).

It wasn't untill the start of the smog era around 1972 that the "performance" engines like the LT1 and L82, as well as big blocks, got flat tops. Almost over night right after all the domes were whacked off, the dished pistons were in everything (by about 1974 I think)

Just thought I'd correct a little mis-info