Compression test?

[Dean Feiock]

Originally Posted by Cam

How does the information from a compression test compare to a leak down test? Which provides the best info on engine condition?
With leak down you can hear the air leaking and determine if the probelm is rings, exhaust or intake valves.
In stock what are good leak down numbers, when is it time to re ring or do the valves?

Cam,
Leak down tests should be used similar to compression tests. All cylinders should test equal.

Having said that, there are many fast stocker motors that leak close to 10%. With the metric rings and ported spacers many engine builders are using, static ring seal is very low. But under combustion pressure the rings seal fine. If your trying to diagnose a ring problem, careful examination of cylinder wall and ring wear is a better choice.

Perhaps the best answer to your question would be to know what your motor leaked when it was new. You could then check it later for loss and variation.