5_02ls1

iTrader: (20)

i have a set of 317 6 liter heads im wanting to port and install on my car....i have reaserched and learned the only difference between these and the 243s are there larger combustion chambers....72cc....i found a couple of threads that stated .030 would put me back to stock comp ratio....does this sound accurate???and does anyone know if a ms3 would clear with this setup....im running a smallish cam now and its not what i want...and anythings gotta be better than my stock 806s....

smask04C5

iTrader: (1)

mill .006 for each cc. .030 would get you a 67 cc chamber. Use some .040 cometics to better the quench. You are correct, the 317 are similar to the 243's. 317's come on all marine 6 liters we install.

Dragkid1917

iTrader: (2)

i have the same question with the 241 heads and a tsp 233/239..... im just gunna do a ptv check with no gaskets, cuz thats .052 thickness less then with a gasket and if it works imma mill em .030 and get a .020 thinner gasket. Btw does anyone know the ptv clearence you should have if spinning up to 7k rpm?..

smask04C5

iTrader: (1)

depends on the valvetrain stability at that speed. I've run as tight as .080 and .060 but with Ti valves on a stout mech. roller. spun it to 8800 on a regular basis twenty years ago.

hammertime

iTrader: (1)

LS1 engines have a positive deck clearance, meaning that the piston extends above the deck surface of the block at TDC. It's damn near impossible to check the PTV clearance without the engine at TDC, which you can't do without a gasket.

Minimum recommended safe clearance on a hydraulic roller is .080" Intake / .100-.110" exhaust. Don't use clay, do a search on the proper way to measure PTV with a dial indicator and checking springs.

santiago

iTrader: (28)

i run 317 milled .40 with the cam in my sig....i have -8cc pistons though. my comp is right around 11:1

hammertime

iTrader: (1)

and it looks like you are running a 408, while it would appear that the original poster is still on stock cubes

5_02ls1

iTrader: (20)

yep stock cubes....anyone else???

ShevrolayZ28

iTrader: (4)

Skip the milling and get a supercharger

5_02ls1

iTrader: (20)

wouldnt go well with y 200 shot

5_02ls1

iTrader: (20)

ttt anyone know if .600 lift will clear???ptv

ShevrolayZ28

iTrader: (4)

There ya go

See if I can help.
Stock combustion chamber on ls1 is around 67cc, that has an SCR of about 10:1.

https://ls1tech.com/forums/archive/i.../t-111207.html

Now I've read that changing to a 72cc combustion chamber will lower compression by about one point to 9:1.

https://www.patriot-performance.com/...&cat=35&page=1

So, roughly, the relationship is for every 5cc of chamber volume, the compression ratio changes by one point.

Another approximation....1cc change in chamber volume per every 0.006" milled.

So the above would lead me to think that to get back to 10:1, assuming you would be using a stock thickness head gasket, you would need to mill 0.030".

As far as P/V clearance, sorry, I have no idea. I would definitely want to assemble it and measure before going to town with the milling.