Guys,

Here are my specs:
1975 L48 8.5:1 comp I believe
bore is .040 over
Hooker side pipes
Aluminum heads (64cc chambers, 180cc runners, 2.02 valves)
My heads are not name brand...chinese knock offs. One guy on here mentioned that this is my problem, but I still think that I am overcammed. If cam #3 doesn't work, then maybe I will start looking for some new heads.

edelbrock performer intake
edelbrock performer 600cfm

I just finished installing my 2nd cam today since sticking these new heads on this motor. I still have not made an improvement on power.
My first cam was a ***** Thumpr....it was extremely over cammed and killed the compression/power (Compression reading were around 160psi). Advertised duration was 235/249 at .050. I then decided to throw the cam I had taken out back in (Crane HMV-278-2). It is not performing well either. It has .050 duration of 222/234, but the intake valve closes late, which killed compression yet again. Compression showed 150psi.

So, I am very frustrated now and I am going to try this again. I am now looking at the Comp Cams XE262 (.050 duration is 218/224). I also compared the intake valve closing point between this and the original Thumpr I had and the XE262 closes 4 degrees sooner.

I am wanting to shoot for cranking compression of around 185psi....do you think this XE262 is going to get me there and maybe bring my engine to life a little?

Sorry this was so long, but I am getting very frustrated! Any help is very much appreciated. I have learned a lot through all of this, even though my engine output doesn't reflect it yet

 

8.5 to 1 is this with those 64 cc heads
10 to 1 compression flat top pistons good heads and a mild cam seems to be the formula for a nice street small block

 

The compression ratio on the original L48 was 8.5:1 and that was with 76cc heads. The heads I installed are 64cc. I left the bottom end alone, so I am not sure what the compression ratio changes to from 76cc to 64cc heads. I am guessing 9 or 9.5:1?

 

You should be at 9 to 9.3 to 1 comp. What are the specs on these chinese heads? That crane cam should make some pretty decent powa.

 

Head specs are:

64cc comb chamber
180cc intake runners
2.02/1.6 valves
good to .550 lift

flow as follows:

Int Exh
.100 74 68
.200 123 109
.300 165 132
.400 206 165
.500 237 177
.600 244 187

I am using full roller rockers.

 

I'm using the Comp XE262 cam in a mild 383 with 9.7 to 1 compression. It makes enough power to run 12.6 at 105, in good air. I think its worth a try in your case.

 

After looking at the intake closing points on the ***** Thumpr and the Crane (HMV278) I am a bit confused by my compression readings. The HMV278 closes 1 degree later, but it showed about 5psi more cranking compression than the Thumpr? Maybe this is an anomaly?

Does anyone know if Crane grinds their cams advanced at all? I know the Thumpr stated that it was ground 4deg advanced.