Leak down testing (not strictly EFI related)

Johnny johnny at johnny-enterprises.com
Wed Jul 16 03:21:48 GMT 1997


Tony Bryant wrote:
> 
> R.e. Leak down testing.
> 
> What units is leakdown typically measured in?
> 
> What are some example good and bad numbers?
> 
> And what pressure does the cylinder get pressured
> to?
> 

Typically, you would use 80psi on the supply side. In aviation, again
typically, when the cylinder gets down below 60psi, it won't pass. In
racing, it's usually used to find the bad hole and listening where the
air is escaping from will tell you pretty much exactly what's bad about
it.

All it is, is an orfice of known size between the supply side and it's
guage, and the cylinder side and it's guage. The more the leakage, the
higher the differential from one side to the other. If you run 80psi on
the supply side, I would expect at least 70psi on the cylinder side. If
you can't get that, then listen for where the air is leaking. If you
hear it in the intake manifold, the intake valve is leaking, headers
means exhaust valve and so on. Most of the time, I consider valve
leakage to be cause for pulling that head and taking care of it, while
ring leakage is going to always be there a little bit, and you just have
to make the determination of what's acceptable to you. It is a very good
device for finding the weak cylinder, and for telling you exactly why
it's weak. You can also use it to log trends across all of the
cylinders. If you do a leak down every time you do a tune up or other
routine maintenance, and keep a record of it, you can get a pretty good
idea of cylinder condition, and it will take a lot of the guess work out
of troubleshooting when something goes wrong.

-j-



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