I've got a 396 bbc behind a 4 speed and a 3.07 gear. For a while now, I've felt like the engine had a lack of power. (despite the gear)

The cam is a comp cam magnum 270 hydraulic (224/224 with 0.510 lift). This runs with an edelbrock performer rpm intake and a holley 750.

I've finally pulled the engine and tore it down. What I found was 820 open chamber heads giving me a compression ratio of 7.9:1!!!

If I find a closed chamber head (101 cc), that only brings my ratio up to a 9.0:1.

I'd like to get my compression at 10:1. The application is the weekend driver on pump gas. I'm not interested in racing but do like to hammer it every so often.

So here's my questions for you guys;

1. If I stay with the 820 head, is there a domed piston big enough to get me to 10:1 compression?

2. Is there an advantage to sticking with the open chamber head vs finding a closed chamber head?

3. Even if I go with a closed chamber head, I will need to replace the pistons. Is there an aftermarket head (cast iron) that would get me to my target compression or am I bound to buy new pistons? What pistons do you recommend?

4. Other comments?...

I'd appreciate your comments. Thanks.

Dave

Look at this chart! (http://www.flatlanderracing.com/trwchevy396_427.html)

scoobydoo i have been in your shoes..... when i had my first big block 396 rebuilt by a machine shop alot of years ago....i was told my engine had 10 to 1 compression and they put in a 272 crane cam........when i started to add bigger cams and intakes and carbs my car was slowing down bad........thru the 1/4 mile.....

i tore the heads off (my mentor at the time believed i didnt have the compression as stated and thought that was my problem)and come to find out i had 7.7 to 1 compression!

my pistons was cheap replacements that had a small dome that was worth about 10cc and they was cut for the intake valve on both sides so the piston could be placed in any hole. the pistons was down .055" in the hole and had thick head gaskets with 118 cc open chambered heads.

i found a set of closed chambered heads that was factory rated at 96.4 cc and added steel shimmed head gaskets to get it up to close to 9 to 1 compression.

this made a big difference in performance.

later on i wanted more compression so i bought the trw factory replacement 11 to 1 375hp 396 pistons.....this brought my compression to 11.7 to 1 with the same heads and steel shimmed head gaskets and my deck height was around .020" now with those pistons.

if memory serves right those pistons had about a 36 cc dome on them and if you would buy them and use your heads and a set of steel shimmed head gaskets your compression ratio should be around 10.3 to 1 about 9.8 to 1 with .039" head gaskets.

i think this would be your best bet just buy the 11 to 1 375hp trw 396 pistons and run with them.

Your # 820 heads have a combustion chamber around 113cc. An easy and quick fix would be to locate a set of 1965 #206 heads they have a 97cc chamber/ 66 #702 head with a 98.5 chamber/ 67 #390 head also a 98.4cc chamber. Any of these heads should bring your compression to 9 to 1 or a little better. This would also save U the trouble of a complete tear down of the motor. U shouldnt have much of a problem locating a pair of these early castings, but if U do I have a set of the 67 #390 castings.