quick compression question

[AWSpoofwil]

What's the stock l20b compression rate? Can't seem to find it.. found the ratio but not the rate.. :/

[ggzilla]

Rate? That term does not apply to compression.

[AWSpoofwil]

Well I mean stock psi

[ggzilla]

Pounds per square inch?

 

Are you talking about a Compression Test reading? That number is meaningless. I've got different gauges, they read different amounts. What is important is: 1) The relative reading. All four cylinders should be within 15% of each other and 2) The relative Wet and Dry compression reading. It should be the same.

 

If you read the instructions that come with the Compression Test Gauge, it will say that absolute numbers are not to be relied on.

 

See Engine compression test How To

[datzenmike]

The rings and valved don't seal perfectly, even less when worn.

 

The cylinder volume on an L20B is 487.75cc but not all of that volume is actually compressed. This is because the intake valve does not close until the piston has passed the BDC point by 52 degrees! Vertically, the piston is about 15% of the way up the cylinder. At cranking speeds, by the time the valve closes, about 73ccs escape back into the intake.

[Sealik]

Well I mean stock psi

 

 175 PSI + - a couple of lbs between cylinders would be a very good reading

[ggzilla]

150 psi + - a couple of lbs between cylinders would be a very good reading, also

 

175 psi dry with 190 psi wet means bad rings

[datzenmike]

Yes,  generally 175 and above is quite good.

150 still ok, will run great, good oil mileage

130 is getting worn

120 worn but if all cylinders even will run fine, probably burn a little oil

110 and under needs rebuild, but again if even will run smooth but be a bit tired.

[Sealik]

150 psi + - a couple of lbs between cylinders would be a very good reading, also

 

 

 

 

Correct...but I'd rather have 175 across the board..... and maybe a 3% loss on a leak down test.... :P

 

 

 

[ggzilla]

Mike, we've gone over this before. 150 psi can be VERY GOOD or BERY VAD. Read the instructions that come with your compression tester -- it's not the number, it is the variation.

 

A $200 calibrated Snap-On compression tester might read exactly, but most of us are using less expensive u-ncalibrated $25 compression testers.

[ggzilla]

An OTC leakage tester is fine, but a basic compression tester can give good results if used properly (i.e. using dry then wet tests).

[datzenmike]

I guess I didn't say even on all.  :blush:  175, 175, 150, 175, is bad. 150, 150, 150, 150, is ok.

[AWSpoofwil]

okay thank you everyone! im gettin about 150 in all of them! :D

[ggzilla]

Good, the engine will run well with that. If you want to know what condition the rings are in, do the wet compression test. If it goes up then the rings are burning oil.

[AWSpoofwil]

good to know, thank you!