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Not really relateable in the real world, what numbers are looked at as good there are way above what you find on most engines, even ones that run pretty good.

Used more for drag racing where the last 5% loss can kill you. You can lose 5% in 30 seconds of running on a street engine at first startup. Many engines can be hard to get above 95% on even once and before running the engine at all.

Even a 'bad' 15% leak is pretty good on a street motor with some moderate mileage on it.

Why I leakdown on race engines but compression test on street engines.
 

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Old Phart
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Decent short video on leak down testing, it's generally used for diagnostics of a problem found with the "screening" of a simpler compression test.

Great to do before tearing into an engine with an apparent issue, can't get that info. once it's torn apart & occasionally it'll reveal an issue that might be fixed without a tear down.
 

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This is such a great post, thanks for sharing, NJSVTGUY or Tom?. ...... I'm a newbie and this is so helpful.
 

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Discussion Starter #7 (Edited)
Part 2
Took head to machine shop. Looked great when I picked it up but failed on cyc #4 exhaust side.
1-3 held great. Going back on Monday, called and no issue at all..."bring it back".
Glad I checked.

This vid shows 80psi going in and the head only holding 60 psi. You can hear the air leaking. So not only can you troubleshoot with the leakdown tool, you can test with it.

https://www.youtube.com/watch?v=8GOrF5dpo_s
 
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