Thanks Duke for the training, for some reason I have never attempted to really study and understand camshafts, I always had friends or co workers to lean on when it came to choosing cams. I consider camshafts a special product that I don't fully understand but I am clear on large cams dropping cranking compression. I knew a guy with a 67 Corvette, he owned a machine shop, he raced the Corvette when he was younger and his 327 had 13.5 compression. When he converted that car for street use he installed a larger camshaft which killed his compression and made it able to run on pump gas. Stupid way to go about it since efficiency was in the toilet but it was faster than tearing down to replace pistons and he did it. He ran like that for several years and then sold the car. I almost bought it since it was an original 427 coupe and the body was in great shape he was providing a standard bore 427 block, heads and crank with proper date codes with the car, this was 2005 I believe. He asked $20 grand and wanted a quick sale because he had another car he wanted to buy. I went home discussed with my wife. As soon as I told my wife she pulled out the check book and wrote a check for it came over and handed it to me. I called him back and it had sold. I had no interest in his high compression 327 but that could have been fixed quickly.

 

Low compression in every cylinder can be caused by cam profile, as mentioned. It can be caused by large chamber heads or pistons too far down in the hole for the application (wrist pin location). I have also seen it caused by a timing chain set installed retarded a tooth. 120 psi generally means a ballpark CR of about 7.5--8.1. My '61 Corvette with a 383 has dished pistons for about 10:1 CR, and has 195 psi in every cylinder. My '65 GTO with small chambered heads has 11:1 CR but only 175 psi compression in each cylinder due to a large cam that bleeds off cranking pressure, as Duke stated. It needs race gas to run. The '61 runs fine on 91 pump gas. If your car is not a dog on the bottom end with 120 psi compression, ,I would simply drive and enjoy the car. If it has no blow-by and is not turning the oil black or using oil, no need for a cylinder leakdown test.