Way back in early summer had the intake and exhaust valve springs out to test spring pressures and noticed air leaking out with air pressure to the cylinder to hold the valves up. No amount of turning of the valves to clear any crud would reduce the leakage.

After getting the springs back installed, tried a leak down test cold and all were consistent except number 1.

So I ran the car a few races and retested with warm engine. Seven cylinders showed a leak rate of 19% with number one at 37%. The leaking cylinder still shows compression of 150 psi. Other cylinders range between 150 - 160. Sounds like most of the leak is coming out of the exhaust valve.

What do you think ?

Way back in early summer had the intake and exhaust valve springs out to test spring pressures and noticed air leaking out with air pressure to the cylinder to hold the valves up. No amount of turning of the valves to clear any crud would reduce the leakage.

After getting the springs back installed, tried a leak down test cold and all were consistent except number 1.

So I ran the car a few races and retested with warm engine. Seven cylinders showed a leak rate of 19% with number one at 37%. The leaking cylinder still shows compression of 150 psi. Other cylinders range between 150 - 160. Sounds like most of the leak is coming out of the exhaust valve.

What do you think ?
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I think you have a leaky exhaust valve :D
Also, 19% is unacceptable leak-down in any cylinder in a fresh engine, why is it so high & where is it going?
I do not see any more than 8-10%, usually more like 2-3% in a fresh engine.
It is not unusual for some exhaust valves to leak big time cold but normally will seal after warm-up.

Thanks Mike, will pull heads this winter and see what is going on. For sure the number one exhaust has some sort of problem. The other reason beside testing two valve springs was to cycle through a check for piston valve clearance, which turned out to not be an issue.

Before I do that however, I am going to do another leak down test with another brand of leak down tester just to confirm the 19 % that I got to start with is a true representation of the state of the engine.

If the 19 % is confirmed I agree it is pretty bad for an engine that is relatively fresh when the number should be down at least under 10 % range or less as you say.

Funny thing it starts and runs perfect and is pretty consistent around 119 mph with a cam (and maybe valve springs) that I think is limiting the top end. Doesn't want to go much above 6600 through the traps.

This is a 454 with 049 iron oval port heads. Should have mentioned that the pistons are sealed power hyper cast pistons which should have a fairly tight ring/cylinder seal.

Probably this is a good example that just because an engine runs good and has decent and even compression pressure, the leakdown test is much more revealing about the actual condition of the engine sealing.