jag1886

I took a ride up to Oregon a couple of months ago and noticed that my car was pinging on mountain grades at 55 MPH. Today I compression checked and it has a 195 LBS.
I have a true 10-1 350 and my engine guy insisted on a little RV type cam, I questioned him 3 different times on his cam choice (I was worried about pinging), 3 times he said there would be no problem, I'm a bit pissed.
I also have a small problem with the engine running a little hot, I believe this is a byproduct of excessive pressure, am I correct or not on this?
I don't really don't know what to do about this, I don't want to install thicker head gaskets and ruin the nice squish band I have now and changing a cam in the car sounds like a real PITA.
What would you guys do about this?

TripDeuces

Other than changing the cam or the head gaskets you have a few options.
Less timing
Water/methanol injection
Octane additives or race fuel mix

Personally I've been down this road and all three of my suggestions suck. I had 230 psi so you have it a little better. You're correct in assuming the cam is the problem. You need a bigger cam with more overlap to bleed that pressure off. Changing the cam, although maybe a pita, is your best bet. If you could get the psi in the 180 area you'd be happy.

kirkwoodken

Increasing overlap does not "bleed off" compression. Cranking compression is determined by intake closing point and combustion chamber size. Overlap occurs way before the intake closing point.

Increasing overlap does tend to increase exhaust dilution of the intake mixture, which will result in slower burning mixture mixtures and poor power output at a specific RPM.

To the OP: the "Right" cam, with the right duration and the right intake lobe centerline WILL reduce your cranking compression.

MDchanic

Are you certain that your vacuum advance is properly dialed in?

- Eric

young olds

I am interested in this topic, my nova has a 9.6:1 engine and 220 cranking pressure. I get pinging when pulling up hills in high gear and a little when getting on it hard, also seems to run hot. When I back the timing down it runs bad, I usually run 87 in it but started pumping 89 in but i dont drive it enough for it to be all 89 yet. Curious to see what you come up with to reduce pinging.

TripDeuces

The bottom line is you need more duration on the cam. More duration usually comes with more overlap unless you're spreading the lobes out farther to the point you reduce overlap. Then you get a RV cam like you have now. Although secondary to intake closing point overlap is a part of the equation. Cams have always been a give and take scenario. Your problem is not static compression but dynamic compression, This article will do a better job of explaining my point.

http://www.empirenet.com/pkelley2/DynamicCR.html

TripDeuces

Dynamic Compression Ratio Calculator

http://www.wallaceracing.com/dynamic-cr.php

wild70

don't forget altitude will make a big diff. Not sure if gets leaner or richer. 195 lbs is compression dream usually indicates correct cam 180 or less junk it.

jag1886

Maybe 30 years ago 195 would be a dream. I live at 3100 ft if I lived at sea level I'd probably already have holes burned in things. Everything I read says 160-180 is good for todays gas. Going to add a considerably larger cam, I think it's the same cam I tried to get my idiot engine guy to use in the beginning, he was with you, he said I'd have no problem with pinging because of our altitude, man was he wrong and I guess that makes me an idiot for listening to him.