I am trying to get my pistons ordered by Friday. Im looking in my Competion Products catalog and The JE pistons im looking at part# 105038 will give me 10.8 compression )I looked up the same part # in a different catalog) I called CP's tech line and he said, "did you have the block decked" I replied, "No" Then he said,"Those figures are done with a zero deck block. Since the pistons will be "in the hole" (he said .20 or .30) That should give you the lower compression you need for the street." (I want around 9.8-10.3:1. Do you guys think that since I have not decked the block and my pistons (at the highest point ) should be around .2 or .3 in the hole. that I should be okay running with these pistons? Sorry Its late at night so I might not make perfect sence. But Thanks in advance for your help,
Chris

 

These pistons are designed for and spec'd out with a 3.5"
stroke crank.
On a 4.030"x 3.50" Odecked motor with 6" rods
and 64cc heads with a 9cc felpro gasket (.041") the cr would be
10.76:1

IF*** you build your motor with a stock 350 3.48" stroke crank
using a undecked block and 6" rods These pistons should be .035" in the hole, resulting in a cr of 9.84:1 with the same gasket and head.

If you used the factory type .015" shim gasket, the cr
would be 10.52:1 and your quench clearance would be a lot better.

A .028" gasket would get you 10.19 cr

 

Thanks alot F-Bird So will I be okay using these pistons with the 3.48" stock stroke crank? okay well I think the compression with the stock .015 gasket is alittle high. Do you think the .028" gasket well give me a decent quench area?
Thanks again, now I can order my pistons!

 

The idea is to have a final quench clearance including the gasket
of .040" to .055". More than .060/.070" is too much.
Your motor will still run, but won't be as good as it could be.

If I were building that motor I'd do some deshrouding
and cleanup in the combustion chambers to add head cc's
to allow a tight quench with reasonable compression and pick up some low lift flow in the process..

The only way to know for sure what your final deck height will be
is to either measure the parts ( block, pistons, rods,crank)
or pre assemble the motor and check. The factory block height is
9.025" but production tolerances vary. I like to check deck height
of the factory motor when I tear down a core, then mark that block for future reference.
You'll have to decide on your cr depending on the available gas in your area and engine design.

You can download a good demo compression ratio calculator
(Windows based) from Performance Trends and play with the
numbers yourself. The Keith Black site has good online calcs
and lots of info too.
http://www.performancetrends.com/

http://www.kb-silvolite.com/

 

Thanks for your help F-bird, I have 91 and 93 easily avalible. I guess I will do like you said and take away a few CC's by deshrouding the combustion chamber. and run a .015" gastket That should get the compression in the mid 10's. I found these Fel-Pro gaskets. http://www.sdpc2000.com/cart.asp?act...id=575&pid=712 will these work?

Thanks alot,
Chris

 

Yep, they'd be the ones....