NightMoves

317 heads on 5.7L look like they would only have a CR of about 9.3 if I have figured right. How much should they be milled to get up to about 10.3 to 10.5 CR?

TJ

iTrader: (10)

around .030 maybe more?
dont forget to factor in PTV clearances if you are running a stout cam.

JoshuaGrooms83

iTrader: (2)

has a simular question but im thinking of running 317s on my boost build.
im not sure if im doing the math right or even if i have all the right data for the calculator casuse some of it is confusiong me.
does this look right for comprtession ratios and data.
LS1 standard sizes (i think)
Enter Cylinder Bore Size-----3.90
Enter Piston Stroke Length-------3.6
Enter Head Gasket Bore Diameter-------3.90
Enter Compressed Head Gasket Thickness----0.053
Enter Combustion Chamber Volume In CCs -----66.9
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') ---0
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') -----0.002

with this calculations,
Static CR is 10.16:1

now if this is correct now entering the 317 heads unmilled data with thinner gasket and this is what i got:

LS1 with 317 head sizes (i think)
Enter Cylinder Bore Size-----3.90
Enter Piston Stroke Length-------3.6
Enter Head Gasket Bore Diameter-------4.05
Enter Compressed Head Gasket Thickness----0.040
Enter Combustion Chamber Volume In CCs -----72
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') ---0
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') -----0.002

with this calculations,
Static CR is 9.8:1

Now if thats the right estimated calculation, would the 3 points of CR lost be even notice able? this slight drop in compression is what helps keep detonation down and able to crank up boost. Am I correct? need others with a bit more input.
I used this calculator for my reference. http://www.csgnetwork.com/compcalc.html

87DodgeD150

iTrader: (18)

I used to run 317's before I went to ported 5.3's. Mine were decked .015 and from what TEA told me my c/i was low 9's and you would need to take a good chunk of metal off of them to get even close to 10.5. Also he mentioned how much the combustion chamber layout or something would hinder performance.

Like TJ said, check your ptv if you wish to run these heads with a large milling job. These are more of a boost head than a n/a head, hence why I switched.

JoshuaGrooms83

iTrader: (2)

for me, im trying not to mill mine. at least not alot if i can get away with it. im trying to lower my compression a little without lossing a TON of CR.

JoshuaGrooms83

iTrader: (2)

ive been playing with the CR calculator and im getting alittle more compression with certain numbers, for example
5.7L LS1 block, stock rotating assembly
317 heads - 72cc
different gasket thickness
cometics .040 w/ 4.010 gasket bore- 9.9:1 CR
LS9 gasket .051 - 9.8:1CR
Stock MLS gasket .056 - 9.7:1

so would a cometics gasket keeping the CR nearly close to stock CR be ok to run on moderate boost like 14psi?

JoshuaGrooms83

iTrader: (2)

any updates since last time?
I'm valve springs and head studs away from doing 317s, LS9 gaskets, and a 226/230 cam on my LS1.

JoeNova

Why would you not just run stock LS1 heads?
Milling the heads reduces deck thickness and PTV clearance and you're BARELY getting a drop in compression.

JoshuaGrooms83

iTrader: (2)

I myself have a 98 block with the the 98 heads with the graphite gaskets and notched heads still in the engine compartment from when gm put it in there lol. Plus i picked up a set of 317s cheap. Im running a gt45 turbo with at least 10psi when its all said and done. The cams a summit pro stage 2 turbo cam. By the math my cr will be roughly 9.8:1 on the old 5.7L and gives some room for tuning as well.

jjzepplin

I am also wondering about this combo. I have a 1999 5.7 and a set of 317 heads as well as the stock 853s. I am replacing the 5.7 with a 6.0 and AFR heads so I have these leftover parts and don't want to give them away and thought I would set up a turbo engine for my next unknown project. Have you built this engine yet?