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?

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.

 

you have knock with that cam on that motor? i'm kinda surprised. 8.7 you can still get away with pump gas 93 octane and decent tune. AFR's wont need much timing to make power, mine does best at 34 degrees but i've tried 38 on the dyno and worked down and power just kept getting better, even tho the motor got hotter. I never had spark retard or knock counts even with fairly lean midrange and 38 degrees and i'm at 8.3 to 1 dynamic. (230/245 on a 109 lsa, installed 108 icl, 71 degree Intake Closing)

Either way i think that bigger cam is much better choice. It will rip!!

I'm thinking its probly because that truck is pretty heavy its loading the engine up more and hence the knock. But is the cam installed correctly? did you add advance or retard it? Did you degree it?

(EDIT) I see its plus 4. Install it straight up (112 icl instead of 108) and it will help out. delays the intake closing abit more to make it act like larger grind

 

Yea, I believe for a weekend truck, the bigger cam would be the way to go especially with the bigger exhaust split b/c of my 1 5/8" headers. That would like the exhaust have a little bit longer to breathe and support the engine in the higher rpms better.

Yes, the heavier weight of the truck is what hurting me I believe. However, the cam peaked in a 383 LT1 with LE2 heads at 6100 rpms on the dyno and carried to 6400 it looks like so should be a good cam esp. when I want to shift around 6300rpms.

My A/F ratio is 12.5. We have 93 octane here but with the E10 fueling...I believe that's hurting me a little bit on timing is that ethonal.

Oh, I also installed the camshaft currently straight-up.