Leak Down Test?

[ssheen]

Is it necessary to have the cyl being tested at TDC? Or can one just take the followers off to have the valves close?

What is a good % for a leak down test?

[puppet]

TDC is where the piston makes power. It's also where the most wear will be.
Testing in another position doesn't tell you a whole lot.

Good % for a turbocharged engine? It's gonna be more than for an N/A. Could be as much as 15% maybe a tad more. Depends on what you've got for ring end gaps. Consistency across all cylinders is more important. Obviously, if one reads 30% while the others are at 12% or so ... you know that cylinder has a problem.

I won't get too hung up on % of leakdown as it relates to ring condition. If they're all within close readings but a little lower than you think they should be ... your in for a lot of work to gain maybe a few % points equaling maybe 3-5HP overall. *If you've done the test right in the first place. Bigger gains are to be had for less headache. The test is meant to determine where leak problems reside. ie, valves, BHG, broken rings/lands and of course bad/worn rings.

Example: car is burning oil and smoking. You're not sure if it the turbo, valves or your rings. Plugs look ok ... maybe a little oil. You perform a leakdown test to point you in the right direction. No sense in tearing the engine down till your sure of where the problem is.

[ssheen]

Thanks for the info yet again. :D

[turbovanman²]

2-4% is where you should be. 10% or more and its time for a ring job or a valve job. If you have alot of blowby, 20% or more, listen in the tailpipe or intake, you can hear it leaking out.

[Lee'sdaytona]

Example: car is burning oil and smoking. You're not sure if it the turbo, valves or your rings. Plugs look ok ... maybe a little oil. You perform a leakdown test to point you in the right direction. No sense in tearing the engine down till your sure of where the problem is.

That is my situation exactly! I just finished building my leak down tester today. I'm praying for a bad turbo:o
-Lee

[Lee'sdaytona]

Ok I went out to try it. I think I'm doing something wrong. I brought the regulator up to 100 psi and then backed it out, and all the air escaped through the regulator. Are you supposed to just shut off the compressor and not back out any regulators which would release air?
thanks,
Lee

[puppet]

Bring the gauge to 100 with the regulator and plug it into the adapter you've already put in the sparkplug hole. Do not touch the air compressor (ON) or the regulator anymore (you just set it). Read the gauge.

[Lee'sdaytona]

ok well doesn't the air compressor keep pumping air into the cylinder though? So I could set the compressor regulator to say, 110psi, and the leak down tester to 100 psi, and leave the compressor running and then hook the hose up, and it will just drop a little? (hopefully that is) I did the test for #2 and it went down like 8%, and then cylinder 4, the one in question and I stopped watching it after it got down to 40%...but that was with the comressor turned off, after it had reached 100...I'll have to re do it tomorrow.
thanks again,
Lee