If my 340 is 10 to 1 compression how much should the compression gage read?? 150# or 160#?? I had a 12 to 1 and it had about 180#

Depends on the cam etc. I would just make sure they are all pretty even between them.

thanks for the reply, I just checked two cylinders and the were both 160, so I think all is well.

How do you know all is well if you didn't check all eight cylinders?

Remove all the spark plugs - then check each cylinder with no plugs in the engine at all.

This way if you have a leak between two cylinders you wont get false reading.

A little more info would be helpful - why are you testing compression?

Its a fresh motor just changed the cam, and it was running sluggish, so I was concerned that the cam was in a tooth out (retarded) so if it was, the compression would be low, not sure how low, but for sure not 160#.Had the timing at 37deg. had to go up to 45deg for the motor to act rite, got lots of power at 45. I think my timing lite is toast.

"SHOULD HAVE DEGREED IT IN"