Compression question (317's on 5.7)
 

Came up with this compression # with this calculator. I used .051 gasket (-) the ~.007 the piston comes out of the hole for a total of .044 in the last field. Is 9.9 correct?




http://i42.photobucket.com/albums/e3...ps6ccfd68b.jpg

Really?

Yep....Sounds good to me.

Why does everyone say it takes you down to 9.5 or some even say lower? 9.9 is fine for me, I just don't want to put them on and have it be w too low is all...

That's a pretty generic calculator. It doesn't factor things like gasket bore, or crown to ring volume. After you factor all that in it would be a little lower.

^^Like bww said, it is not factoring in gasket bore and such, but 9.9-10.0:1 is about right anyway, and good enough in most cases!

Stock compression on an ls1 is 10:1, jumping up almost 5cc's in chamber size will probably drop it to around 9.5.

Also, considering the 10:1 stock compression of the lq9, being the only difference between these two instances is the larger bore, 9.5:1 on a stock ls1 with stock 317's is more believable than 10:1

He's not calculating using a stock thickness gasket though :) I ran it through my calculator to verify the numbers, using several different bore size gaskets too, which makes very small changes only.

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


I just used this one and got 9.78

-LS9 gaskets (4.100 bore, .051 compressed)
-.007 out

That'll work for me. I think I'll have them take .005 off when resurfacing, should be good to go. I just wanted to make sure I wasn't doing something incorrect. Thanks guys.

Why would want the lower compression? The int/exh ports and valves are the same...you can get a set of ls1 for $100, if you are getting or have a cam it will prefer the higher compression

Because I'm throwing 12-13lbs of boost on a stock bottom end... And yes I'll have a CCP grind cam (222/230 115). It should be a tick above 9.8:1 after being resurfaced.

I went from the setup in sig to FI. My old LMS 243's were 59cc...

Makes sense...

Wrong...the intake and exhaust ports are the same as ls6 heads, not ls1 heads. They are far superior to ls1 heads in terms of flow.

was wondering. ive been reading around and it seems that .040" gasket size is the one alot people recommend to get to get "optimum" quinch in the camber.

now with that added math,
that puts my stock LS1 at 9.9-10:1 CR (9.7:1 with LS9 gaskets) with 317 heads. with boost in mind, is 10psi "safe" to get HP up to 600ish?

just wondering about which gasket size to go with the 317 heads on my build and which would be better suited for 10psi and under. all things being equal of course. on a side note, im considering the Tu1 or 228r cam for it as well.