Technical > Matt Shaff's Engine Shop

Cranking compression vs. cam timing

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wideopen231:
 Was working on car to day and decided to check CC for reference  for future use. Was way low 150 psi on 1st 3 cylinders. Decided to move cam a little and see it couldn't bump it up. Was set at 33 @ .050. Moved 1*,cc was 165,moved 1 more and it was at 190 psi. Figured to experiment little. I moved another and now at 36* At .050 and 195 psi. Moved one more and stayed the same.Tried another degree and no change so went back to the  36* at .050.  Now this is with cam that 296* at .050 which is probably 10 to 15 more than motor needs. Then have two of these sitting here and no cost. Probably buy another cam later.

 Seems 45 lbs cranking compression increase for 3* is bunch,but again cam is little over requirement for car.

jeff/21:
advacing or retarding cam makes a big difference in how a motor reacts.loosening or tightening valve adjustment does too and changing rocker ratios
when you do order a cam talk to the tech and tell him what  changes made improvement. any additional info he has will help find the right cam.

wideopen231:
With cost of 2500 to 4500 changing rocker set up is not happening. Cams are only 500 bucks,only. As for what car needs I have a cam spec that I am going to get custon ground later on,after some recovery from 3months of seeing how much I can spend and doing dang good job. One thing never changes in racing,no end to how much fun can you afford?

jeff/21:
Some rocker set-ups are pricey we played with various cams and rocker ratio just to come back to what we started with. blown bbc on alky more lift and less rocker ratio didn't find any hp. only no spare parts
so we went backto what everyone  was running

jeff/21:
all i was trying to say was the cam is the heart and and dictates how the motor reactes and use parts similar to the others incase you have to borrow, especially if you run a circuit and are away from home you can't carry everything.

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