317's
 

ive been searching around and cant get a 100% straight answer. if i have a stock 1999 ls1 short block with stock pistons and i install a set of 317's what will my compression ratio be. i keep hearing different numbers and guys telling me that it "should be about" this number but i cant get a straight up solid repeatable number. HELP

how much do i have to mill them to get to 9.5?

did you guys buy them new or used and how much did you pay for a set?

9.5ish

I come up with 9.252 to 1 if you use head gaskets that are .051" thick and 4.065 bore. I'm assuming your pistons are .015" in the hole though. I think mine were close to .020" but my memory is fading fast!

If you need a set of 317s shoot me a pm. I ended up buying a set of Darts for my project so I have a pair sitting around.

the reason why you are not getting straight up answers is becasue you do not give out any information

what headgasket are you planning on using ?

where the heads milled ?

was the block ever decked ?

A stock 99 will have a bore of 3.90

I used 3.898 for the bore size. Your bore size of your head gasket is always bigger and should be matched to the heads you are using and not the bore of the block. Otherwise you could be hanging the gasket into the combustion chamber of the head.

Frank

Ic. Thanks for setting me straight on that :D

No problem brotha! :drive:

With a stock ls1, stock 317s and lq4 head gaskets, you should be somewhere between 9.1-9.2

how much would i do i have to mill the heads to get to 9.5 or so?

lq4 gaskets being the GM ones?

http://www.race-cars.net/calculators...alculator.html put in your info, get your answer.

the reason i ask this is ive heard people claim anything less then 9.5 cr will give you sluggish low speed performance.

You would need the heads to be 69cc to get 9.55. roughly every .005 you mill with give you 1cc so you would have to go .015" I would not reccomend milling the heads. The decks are thin enough as it is. I think 98 heads are 68cc. But they don't flow as well as 317s or 243s.