Just curious if this makes much difference for a forced induction build:

What's best to get the right cr:

A shallow piston dish and big cc head(ex. A 75 cc head)?

Or a deep piston dish and smaller cc head (ex. A 62 cc head)

Or does it not really matter how you achieve your compression ratio
Thanks

 

I'm gunna say a shallow dish and a big chamber.

A shallow dish gives more meat around the top edge of the piston and the top ring land. Breaking off a chunk is a fairly common dished piston failure for forced induction applications. A dish also does some weird stuff with your quench height around the top face, where as a larger chamber is a one open pocket, not sure if this is an issue though.

 

Curious as well. I'm going deep dish, less cc; but my setup is mild.

 

IMO going to depend on the specific designs of the dish and chamber.

 

Either way will work if you can keep the mixture from detonating prematurely.

 

Yep. I had two cracked pistons and that's where they broke.

 

Depends on the design of the piston as said. You want a full dish piston vs a D-shaped so the ring land can be uniformly strong all around, but a good quality piston should hold no matter what if you can keep away from detonation. SHort answer, go with lg chamber and smaller dish if possible. My engine builder told me you dont need to worry about quench much on a boosted engine, and he been building race engines for the last 40 yrs or so. He says its not a big player in the grand scheme of things on boost as in NA engines.

 

What he said. If you're building a fresh FI combo, you're going to detonate at some point. Having a larger chamber and smaller dish will increase piston strength at the top ring land. I've broken more of these than I care to remember.

BTW, for years I used D-shaped dish pistons to increase quench area. However, the last set of pistons I bought were from Ross. Ross made the dish circular instead of D-shaped. This left a lot more area all the way around the piston and, thus, much more top ring land strength. I never broke one.

Keep in mind that the Buick 3.8 pistons were cast not forged, which implies that the geometry of the piston is much more important than the material, so be careful in choosing the geometry.