Im looking at getting a different set of heads to lower the compression down. Its a forged 383 with JE pistons. Do stock lt1 heads need to be shaved in order to reach a compresion ratio of 11.8:1? I believe the rods are 6 inch rods and that JE only makes one piston for a 383. Well anyways I am looking to lower my compression ratio obviously. What head should I choose and how low can I get the compression?

 

well, JE i believe makes a -31CC piston for a 383, which will drop it quite a bit. Also, you do not shave a head to lower compression, look into like a trickflow head or something

 

How much will a trickflow head lower compression?

 

In order to determine the static compression ratio of a motor, you need to have the following information:

Cyl. head volume in cc's
Piston top volume in cc's
Cyl. bore in inches
Crank stroke in inches
Deck Height in inches
Head gasket thickness in inches

Rather than relying on someone else to calculate various compression ratios for your motor, why not use one of CamaroZ28.com's automotive calculators yourself, such as http://web.camaross.com/services/calcs/cr.shtml so you can try different combinations. If you look on Trickflow's web site and AFR's web site you will find the various cylinder head volumes available for the LT-1 motor. You should probably look to get your compression ratio around 8.5 to 1 if you are wanting to run the F1-A.

 

To give you an estimate, i'm running the JE -31's in my 383 with ported LT1 stock castings. There ported to bring it down as much as you can with a stock casting anyway and i believe i'm running right around 9.0:1 or a shade over that. Like stated above, you may want to look into a different head with an F1a.

Ken R.

 

I have no idea which JE piston is in there, but It's not a dished piston thats for sure...pretty sure its a flat top. Its got 6 inch rods, but dont know what the deck height is because I dont have a copy of the build sheet. All I know is that its in the neighborhood of 11.8:1 compression. Im just going to pull the motor again and get some dished slugs and some AFR's and see what kind of power I can make with 20 psi...

 

Realistically, that is the best way to go about it...Good luck with the project!

 

With your compression ratio that high, I doubt any set of heads will lower the ratio enough to be safe (at least with any decent or moderate amount of boost on pump gas). Shaving or milling the heads will raise the CR so, definatly stay away from that.

What you really need to do is look into getting new pistons. I know you are trying to just do it with heads, but to bring it down enough (and you need it down a bit from where you are at), I can't see any way other than changing the pistons.

 

I would recommend going with some true blower pistons especially since you are around 20 PSI. The blower piston specs are around 8.5 to 9:1 compression depending on the heads. Also a good idea might be alcohol. Give it a try, it will bring down the chances of detonation big time