[Meatball]

If a piston manufacturer specs; 10.2:1 with 118cc chamber, are they assuming that there is no added chamber volume from the head gasket? If so, when I add a 10cc head gasket volume am I looking at an effective 28cc chamber?

[BillK]

Don,
Most piston manufacturers assume a stock type gasket (usually about .028") in thier specs. I know that TRW/Sealed Power shows the gasket thickness in the catalog with the piston listings.

Depends on the piston manufacturer,

[d1_bradley]

Bill, correct me if I'm wrong but don't they also 'allow' for the piston to be "down in the hole" some too? Seems that most of the time that if you actually do the math and measure EVERYTHING the 'actual' compression ratio is slightly less than the advertised ratio.

[pdq67]

Right, figure a stock DITH piston of like .025".

pdq67

[BillK]

It strictly depends on the manufacturer. I was looking at some 400 Pontiac pistons today for a customer. Stock cast pistons, nothing special. The pin hieght on 3 different pistons varied almost .020" The difference between the Sealed Power forged an cast pistons was about .010" SO basically you have to look at all the measurements and figure what you have. Most of the "good" forged pistons for a small block are speced for a 9" deck hgt, but most factory blocks are closer to 9.025" Etc Etc .....

[Highway Star]

Don, good question.

[Meatball]

Originally Posted by Highway Star

Don, good question.

Thanks, I was going through a list of pistons for a 496 trying to find a specific compression ratio without having to spend $800 to get what I want. I found some 10.2:1 Keith Black's but I think that is a little high for the combination I am putting together and for the Iron heads I am going to use (781 with 119cc). I figure with a thicker head gasket I can get it down to closer to 9.5:1, I just need to collect my data, break out the calculator and get down to business figuring it out then go from there.

[dmuller]

Most here probably already know about this, but there are some neat compression ratio calculators on the web, like this one:

http://www.csgnetwork.com/compcalc.html

[Meatball]

Originally Posted by dmuller

Most here probably already know about this, but there are some neat compression ratio calculators on the web, like this one:

http://www.csgnetwork.com/compcalc.html

Awesome! Thanks for the link

Don