i have a 69 396 265 hp 2 barrel, that i have put a cc 270 cam and a factory cast intake holley 4 barrel on. so a couple of ?s, are the pistons the same in the two barrell 396 as the 4 barrel 396?
the 2 barrel has 9.1 cr, the 325 hp has 10.25 cr is the difference in the heads or pistons, 063s have 101 cc chambers and the 148s have 112 cc.
according to my old service manual they shared the same cam. so is it all in the heads or are the pistons different?
and is the hp difference more from the compression, or the 2 vs 4 barrel carbs?

Per the Chevy parts catalog ,the pistons are the same (except for 1st & 2nd design which doesn't mean anything here).
Cam appears to be the same also (pn 3874872 id 3874874).
Difference would be compression ,intake/carb and (on some) exhaust manifolds.

Different HEADS (combustion chamber) , and obviously the carb and intake, DAH!

Yep the compression ratio diff is all in the heads, larger combustion chamber. Valve sizes are the same. Cam is the same as 325 hp (weak).

So, put the 063 heads on and you have a 325 horse engine.
You will have 10.25:1 compression (really less than that) so do yourself a favor....
RUN A BIGGER CAM so you do not have too much low rpm cyl pressure.
Run something in the 226-232* duration at .050' lift

So, put the 063 heads on and you have a 325 horse engine.
You will have 10.25:1 compression (really less than that) so do yourself a favor....
RUN A BIGGER CAM so you do not have too much low rpm cyl pressure.
Run something in the 226-232* duration at .050' lift
so now i need to find some heads the cam allready installed is a comp cams 270. 224 @.050 is that close enough? thanks for the imformation guys

What you have will run OK on 9:1
More compression does help.
Will the cost of heads (and any repairs) plus swap time and cost of gaskets etc justify the performance improvement?

the heads on it now possible need a valve job (have a cylinder not runnin right) if i find this to be the problem i will need to pull them off and have a valve job done anyway so ill try and find some 063s or 290s

Steve,

Sounds like a plan.
Get a pro shop to do the valve job. Consider some extra bucks for a bowl blend.