Im running TFS 225s with 65 cc chambers on a stock internal LQ4 and want to mill them down to between 10.8 or 10.9 to 1 with a stock head gasket. Im getting a lot of conflicting information on the internet which is preventing me from feeling real confident with the compression ratio calculators.

I know the bore and stroke but I've seen wide ranging stats for chamber cc on stock 317s (70-74cc) and piston dish volume. Anybody a real authority on the subject? I'd like to be able to fill in these blanks:

63 cc = ? cr
62 cc = ? cr
61 cc = ? cr
60 cc = ? cr
59 cc = ? cr

Im thinking I need to go down to 59cc which would require milling .036 off (assuming .006 = 1 cc) to even get close to 10.8 to 1 but others are saying 61cc (.025) will get me there. So I'm really confused at this point. Thanks for any input .

 

i'll like to know where 65cc head will put me on my LQ9????

 

I'm pulling my hair out already on this and there you go introducing different pistons into the mix....

 

This is what I get.

62 cc = 10.35:1 (would need to mill .018 off current 65 cc chanber)
61 cc = 10.47:1 (mill .024)
60 cc = 10.59:1 (mill .030)
59 cc = 10.70:1 (mill .036)

I'm using the following inputs into a compression ratio calculator:

bore 4.0
stroke 3.622
chamber size 71cc (stock)
piston dish -7.5 (plugged this value to get to stock cr of 9.4:1)
gasket thickness .05 (stock)
piston deck clearance 0

These inputs get me to 9.4:1 which is the stock cr on a lq4. From there I just played with different chamber ccs. Anyone see any flaws in what I am doing here?