I have a stock 350 with dished pistons. I upgraded to 67cc heads to get my compression up a bit, but I would like to get 10:1. I have the engine at the machine shop and they say I need .030 over pistons. I have a friend at the local parts store that will get me pistons at his cost, but I have to get the right part number for the piston I want. He carries sealed power pistons. It there a sealed power piston that will get close to that compression?

 

I would think that two-eyebrow flat-tops and an appropriately decked block to match the pistons would be getting close to 10:1. Are you using aluminum heads?

 

Negative on the aluminum heads. I have Iron Eagle SS 67cc with 2.02/1.60 valves. Should this one do what I'm lookin' for??
http://www.summitracing.com/parts/TRW-8KH631CP30/

 

Go here and download the compression calculator.
http://members.uia.net/pkelley2/DynamicCR.html

You can play around with the numbers to see what you need
Because you have a large chamber size ,
my rough calc has you needing
the block zero decked
a 0.041 gasket x 4.060 dia ( good quench , most important )
and a 5cc dish to get 10:1

The piston you list would give 10:1 with a zero deck block and 0.041 gasket or std height block and 0.015 shim gasket
Both ways give you a nice 0.040 quench.

 

So a standard deck height has the piston 0.025 down the bore?

 

That's correct. Those sealed power pistons add an additional .020" of deck height though, unless that's changed in the last 3 years - so you'd be at .045" deck height.

Since the engine is coming apart to have the cylinders bored, you might as well get it zero decked.

 

How do they add deck height with 1.56" compression height?? They claim 9.6:1 static compression with 64cc heads.

 

The makers quoted figures are only ballpark guidelines; they don't take into consideration things like gasket thickness unless stated.You have to measure for your application

 

Speed-pro/TRW pistons *actually* have a 1.54" compression height. One of their (most widely circulated and duplicated) catalogs listed them at 1.56", so it stuck.

Like I said, unless they changed their pistons in the last few years, this is the case. Or you could always measure a set to verify. .020" is enough of a difference you should be able to measure it with a micrometer.

 

I called Federal Mogul's tech line and they assured me that they were 1.56" compression height. Should I believe the techies? I don't have a set available to measure until I buy them.

 

Is this your first rebuild?

First step - tear block down and bring to rebuilder. Have them confirm that .030" oversize will work in your case. If not, buy .040", etc. Hot tank, etc.

Buy pistons in the overbore size you need. Once in your hands, measure them, or have your rebuilder measure them to confirm the compression height. If necessaryy, zero deck the block, or just do a cleanup cut.

Bore the block to match your pistons (spec each piston to a hole), and install.

Go racing.