Cylinder head discussion 340 with stock above deck pistons

nfhDODGEnfh said
I have a 340 block with approximately 10.25:1 compression bored .040 over, j heads with 72 cc chambers, comp cam xe268h, air gap intake, holley 780, Doug's headers, and a 100 shot of nitrous. 3.55 and a close ratio 4speed. It ran 13.1 last season with the spray. I'm wanting to get a bit more out of it on the track and am thinking about upgrading to aluminum heads. I've seen discussion about how aluminum heads can lower compression by 1 point due to heat dissipation. Is this true? And would the 65 cc head make up for this difference and get me back to where I was? I've been looking at the eddys for the 340 pop top pistons because that already how my motor is set. The shocker 185 wirh 65 cc look good aswell. I know I've seen a few other threads with similar convos but some of them are fairly old and don't address my exact concern. Wouldn't the aluminum head also help me fight detonation against the nos with the better disapation of heat? What heads would you consider to be best to get me down into the 12's?

hi. i am going to try to give you the answers to the questions YOU asked. first things first , your actual compression ratio right now is closer to 9.5:1 ( i get 9.4). you could safely use a 65cc head and get around 10.2:1. that is assuming everyone is wrong and that you have stock replacement pistons (l2316 speedpro or similar) with the top of the piston being 0.018 in. off the deck. that means there should be no problem to use the aluminum heads, compression ratio wont be too high. contrary to others, i would use the edelbrock 340 heads not the 360 heads from them. the 340 heads are relieved in the chambers so the pistons dont come in contact with them. or use the tfs heads, they come cnc ported from tfs, but, not sure about the pistons being too close to the heads on a 340. also, as a rule of thumb, a nicely ported set of j or x heads would flow about the same as a set of un-ported edelbrock heads. have the aluminum head ported, and you got even more power potential. to answer your original question, i gained 2-3 tenths going from home ported cast-iron heads to professionaly ported edelbrocks on a 360 with stock stroke. yes, they make more power. now, if you want my advice, lower your shift points 200-300 rpm each pass till you get to 5500 and give it a real try. and to do like others, here is my recommendation : put some 4.10 or 4.56 gears in the rear before you do the heads ! you will like it, even on the street !