I'm looking to raise the compression on my LQ4 and was going to use a set of 862 (61.25cc) over the 317 (71.06cc) but think i will go with a set of 243 (65cc) to help raise it. The truck will be N/A with a Jegs cam JEGS Performance Products 200582 JEGS Hydraulic Roller Cams - Free Shipping on All Orders @ JEGS and will see alot of cruising time being my DD. Later down the road i might spray it. My question is does anyone know how much safely can i mill the 243 heads to get to 11.1 compression. Thanks

 

Do not run the 862 heads, even tho it will raise your compression, it has a smaller intake valve and smaller intake port. One of the worst flowing heads. Flow>compression.
You can however mill your 317 heads .040 and achieve a 64cc chamber and raise your compression that way. It would basically be like the 243 heads since the 317 and 243 have the same flow characterictics. Would be cheaper than buying a set of 243 heads.

 

Thanks for the reply
What would the comp be with the 317 milled .040

 

Ok after some research looks like if i mill the 243 .030 i will achieve a 11.1 with .051 gasket or mill them .020 to achieve the same 11.1 with .040 gasket. And with the dish pistons ptv should be in the clear but will check when the time comes.

Does all this sound right?