![]() ![]() I don't know how to correct for altitude though, never really had reason to bother. Since you're at a high altitude and have 2.7 psi less atmospheric pressure, I'd say your engine would develop more than the minimum 140 psi at sea level since you're very close to that now. ![]() Note that this is the MINIMUM cylinder pressure, 155 psi should be about right for a fresh low mile engine. All 74-79 TSMs (yes, I checked them all!) state that the minimum cylinder pressure should be 140 psi for all V-8s. The older TSMs don't give a cylinder pressure spec, but 74+ does. Many people add Cam, Intake, Carb and Headers hoping to pick up a bunch of power only to find that they do not have enough squeeze to make it all work. Most modern engines have very little leak down %. If you have air leaking at the carb or exhaust and not the crank case then rebuild your heads. If you have 25% leak down then the motor needs to be rebuilt if you want a high performance engine. If the leak down is 2% you have a great engine but it still may have too low a compression ratio for the cam. Air at the carb is an intake valve, air in the crankcase is rings and air in the exhaust is an exhaust valves. You are watching for leak down and listening for the air that is escaping. The unit has two pressure gauges, one to show the cylinder pressure and the other to show your air pressure in. What you do with a leak down tester is screw the adapter into the spark plug hole and then pressurize the hole with shop air when both valves are fully closed. Excessive leak down can not be fixed with tuning and can only be fix with mecanical repairs. You really should use a leak down tester to determine the condition of the sealing ability of the rings, valves and headgaskets. ![]()
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