What is a Leak down test?

[lazyeye]

Ok, I am a complete noob that is stated in the above question but I sill would like know what a leak down test is, what it measures, where can i have it done, and what are good and bad readings(numbers) for this test like what should test say to mean its good etc... thx, any imput would be appreciated!

opps this was spose to go in tech forums srry

[sykikchimp]

You pressurize the cylinder with air, and see if it holds the pressure. 5% (of pressure loss) is a fair #. lower is better.

If it's leaking too much, you can tell where the problem is by listening for where the air is leaking. like in the valve cover, the exhaust, the intake, etc..

[PSI240SX]

My old KA-T car was measuring as high as %50 in some cylinders but still managed to lay down 412rwhp hehehehe.

[sykikchimp]

lol.. my car had was around 3% on all cylinders last time I checked.

Won't some types of build up's increase % of leak down?