technical advice about compression test on a 2.2 T

[zaza]

Hi gurus... I do not have comparisons tests and I don't how many bars (Psi) should have an engine with good health (1 bar = 14.504 Psi). Nominal CR for a 2.2 T is 8.6

many thanks

[zaza]

up

[72targa]

http://www.pelicanparts.com/techarti..._rebuild-2.htm

From the above article...

So what to do with the results? In general, compression tests are limited in what they can tell you. It is important to remember that different compression testers may give different readings as well. Cranking the engine faster (with a stronger battery or high powered starter) may also skew readings. The most useful piece of information that you can glean from them is how each cylinder compares to the others. All of the cylinders should give readings that are very close to each other. This would generally indicate an engine in good health. A good rule of thumb is that each cylinder should read a minimum of 85% of value of the highest cylinder. So, if the highest reading is 150 psi, then the minimum acceptable reading would be about 128 psi.

[zaza]

Ok, my cylinders are closer. Good new

BTW, the text says values around 150 - 128 Psi that means 10.3 - 8.8 bar that is significally higher than mines :-/

[nullh20]

Did you do the test w/ wide open throttle? Closed throttle will give lower readings.

I am looking at a 71T.

The shop did a compression test with throttle closed & got results of 95-105 psi. He said that this would equate to around 125-135psi throttle open.

I'm not sure why they did it this way, but he claims that the results are still accurate. Does anyone think I trust these?

[zaza]

Interesting... but I do not have the answer. This compression test was done by the mechanic about 6 months ago.

[MattB]

A closed throttle doesn't tell you much because it's creating a restriction. Another point to note is that while the compression ratio does affect the reading, the camshaft timing also plays a major role. Hence it's not possible to deduct the compression ratio of an engine based on a compression test.

[OliveR]

Valve tappet clearance must be done before test.

[sithot]

I recently saw what they use at sanctioned/division roundy-round tracks to determine compression ratios on race engines. It's common name is a "Whistler".

On these particular engines (I believe max displacement is 355 cu. in.) the technical staff "knows" your displacement although they can check that with another test that is quite accurate as well. That "number" is plugged into the "box" and they go after your compression ratio. Too much and you are asked to go home.

Tom

[MattB]

Tom,

In roundy-round racing, they remove the rocker arms so that cam timing is removed from the variables. So in a case like this, they can determine the swept volume of the cylinder. And if the piston is at TDC it could be possible to measure the volume, which with the swept volume will yield the compression ration.

Cheers,
Matt