There is a lot of discussion on this topic, so I thought I would provide some of the info I have on the subject, as well as share my personal opinion/experience.

Here is a DCR Calculator

Here couple articles:
Article 1
Article 2

DCR is used as a GUIDE only to help set up street engines to make good power, if you want to run on pump gas.

Opinions differ, but I think a DCR 8.0 max with iron heads/carb, a little higher for iron heads/injection....maybe 8.3...

Aluminum heads/carb 8.5
Aluminum heads/injection 9

(When I say fuel injection, I am not addressing TBI, but sequential FI, like LT1/LS1.

The use of dome pistons is another world....most street guys are using flat tops with valve reliefs. About the smallest cc for a flat top with valve reliefs is 5cc pistions or larger (more piston volume=less compression ratio). I think I may have seen 4.7cc, but anyhow, this limits a stock 350 to 9.9 to 1 as a maximum available for 64cc heads. You can shave the heads, but that starts moving the pistons closer to the valves, especially when running hydraulic roller cams....even worse with solid rollers because roller cams snap the valves off the seat quickly while the piston is near TDC.

I gotta finish this and go....

One of my setups is 4.030 bore, 3.48 stroke, 5.7 rods, 5cc pistions, .039 thick gasket at 4.166 diameter with the intake valve closing at 67 ABDC which gives 10.51 static compression and 8.24 dynamic compress running RPM heads shaved to 59cc and a carb.

Gotta run...more later...

 

Hey!! I have another minute.

If you take my same setup above, and simply change the stroke from 3.48 to 3.75, static compression jumps to 11.25 and dynamic compression is up to 8.86...which is too high for a carb, but fuel injection would work well.

Fuel injection is more efficient, better fuel atomization where using a carb, the fuel hits the bottom of the intake and dribbles over to the cylinders very inefficiently.....oops...wrong subject.

Now a word about Intake valve closing points. Comp lists most of their IVC at .006 or .004 lift....the solid cams get tricky with the valve lash, but the hydraulic cam data is easy. Just pull the IVC from the card and pop it in the calculator. The calculator says "ABDC@.050 lift plus 15 degrees"...and I guess you add 15 degrees when your IVC data is presented at .050 lift.....but for IVC at .006 lift, that is considered closed.

Another topic into itself is preignition....when pushing your DCR's up to the max for pump gas...you better make sure those head chambers are smooth and deburred around the edges of the chambers and the spark plug hole. My AFR's were pristine...but the edelbrocks were very jagged around the spark plug hole. I just took a screw driver and smoothed the jagged edges out.

Note also, after you surface the heads, one edge of the chamber will be kinda sharp.....don't miss that one either. Smooth the chambers....

Just a few "opinions" of mine that I would think to be generally accepted, but not everyone agrees on specifics.

 

This is the exact reason that my 383 was always near the verge of detonation on pump gas with my 232/240 roller cam. DCR went down enough with 236/244.

So the 236 cam is lowest i recommend to anybody building these 11.2 compression motors.

 

The other thing to keep in mind is that the recomendations are based on empirical evidence using typical aftermarket cam ramp designs. It is difficult to apply the same DCR recomendations when running a GM "old school" design cams because of the VERY SLOW ramp rate near the intake valve closing point.

Other than that I think Pat Kelly's FREE program is the shizznet!

-Mark.

 

That is oh so very true.......technology has come a long way. I cannot wait to get the stock cam out of my 71 base engine......