I have read so many times that you need DCR in the 8:1 to 8.5:1 range if your a GEN I engine on pump gas. Below 8:1 you'll have loss of power. Well...the question really is....my DCR right now stands at 8.7:1 with knock occurring above 31* of timing with 66* ABDC. The cam I'm considering is a 78* ABDC which will give me a 7.8:1 DCR. Is .2 going to really matter because I'll be able to add the timing the engine should have with the lower DCR?

 

if your concerned about 7.8 as opposed to the 8.0 minimum recommended, then no, you'll still have plenty of power either way with those heads and that cam. It will rev up to over 6000 and peak somewhere around 6000-6100 i'd say

There are guys with 10 to 1 compression and those cams with DCR's in the low 7's still making great power.

 

Knowing your DCR is no more or less important than knowing your SCR (Static compression ratio). Neither tells the whole picture. They are just guides, not absolutes. And when you're talking about "staying out of detonation" it get even murkier.

DCR calculations, if taken to the extreme, can basically imply that you can run a 12:1 compression engine on 87 octane if you just shove in a big enough cam.

No. Not the case.

Static compression ratio STILL affects peak cylinder pressures (one determining factor of how detonation-prone a combo is).

What you need to do is choose cam to suit your combination of parts and your intended goals/application and then figure out what compression it will work well with.

Still no substitute for a well matched combination of parts. So whatcha got?

 

Correct and I absolute understand the concept that neither really matter that much but more on the side of the cam specs with the engine.

The engine:
383, 10.9:1 compression, 195cc AFR heads, HSR, Comp XFI 224/230 .547 lift 112 lsa + 4 on 1.52 rockers

New cam considering:
234/242 .540 lift on 1.6 rockers on a 111 lsa + 1

This is for a truck (weighs 4000 lbs)

I have a 3000 stall with 3.73 gears.

Thanks.