Decided to do a compression test on my cammed Z06 since it has just over 103K miles. I disabled the ignition and fuel and had an assistant crank it while holding wide open throttle. All spark plugs were removed and the battery was charged prior.

However I had them crank the engine until the gauge wouldn't read any higher since I figured that would be the max compression the cylinder could produce. But I read that I should take the measurements after 4 cycles. Does it make a difference? Also I realized I left the brake booster unplugged while performing the test? Does this matter?

So far I've gotten the readings for the driver side :205 190 195 195.

Some have said I should perform the test with the engine warm but this isn't Practical and I would think that by the time you reach the last cylinder, the temp would have dropped significantly which could skew the results.

I'd like to know if this is the right way so I could finish the other side tomorrow.

 

I've always tested cold. It's cranking compression anyways. Usually do stop after four or five cycles but it also normally peaks by then.

I don't think the brake booster hose made 2-psi difference.

 

you're looking more for uniformity than any specific number. Results look very good so far

 

The block takes hours to cool if you wanted to try warm.
The brake booster being open is no different than the throttle being open.

 

This is my understanding as well. I think i may continue doing the tests the same way as I have so far just to remain consistent.

 

I decided to do a compression test on my bolt-on 2000 WS.6 a few weeks ago since it has 234,000 miles. My results were:

(8) 165 180 (7)
(6) 182 180 (5)
(4) 180 180 (3)
(2) 173 170 (1)
FRONT

The needle on the gauge would level off on about the 4th compression stroke. In case you're curious OP - I started on bank 1 (drivers side) while the engine was pretty hot. I didn't get around to number 8 until after dinner several hours later. I don't think it had any impact on the numbers (because the block was still somewhat hot to the touch), but number 8 was a little lower, so who knows.

Best pass a few days later was 13.11 at 112.87mph so I guess I'm just going to keep running the hell out of this old LS1. That was in 83 degree weather (about 2675 DA) with a 2.16 60' (M6 with 3.23's and street tires). I want to go back to the track when the air is cool and crisp bc the old bird loves that stuff

 

I pulled plugs on aluminum heads years ago and ended up damaging the threads so I've always done my compression testing on cold motors. As mentioned above, uniformity is what you are looking for.

 

So I started doing the passenger side today and I'm noticing it takes a lot more than 4 strokes to max out the pressure. When it maxes out its reading about 190 or so but like I said its taking a few strokes. Am I doing this right or am I fooling myself?

I don't think an engine can make more compression than it should with more strokes since it eventually maxes out any way.

 

Try this - squirt a little oil into the cylinder. See if it build faster.

 

I'll try that tomorrow and see if it changes much. I know it should change somewhat though. I'll probably try doing it all again with a warm engine.

Btw the results today were in like with yesterday. 200 190 195 195

 

If adding oil makes pressure build faster or higher it would mean the rings are worn.