Have been doing some diags on my car and my compression test came out to 150, 145, 140, 150 PSI for cyls 1-4. Car was warm, all plugs out, Fuel pump fuse pulled, throttle plate 100% open. Plain old NGK heat range 8 Plugs have no oil on them at all. Searching on compression test showed most 11:1 stockers pulling 210 - 240 PSI. I'd figure there's a drop going from 11:1 down to 9:1, but 60-80 PSI seems like a lot. Here's my reasoning:

2.0L 4 cyl displacement = 500cc of volume per cyl.
11:1 CR means it compresses a cyl's 500cc of air/fuel mixture into 45.45cc "in the chamber" at TDC, and we'll figure the 220 PSI our stock guys quote is reasonable.
9:1 CR only compresses that same 500 CC into 55.56cc of chamber - less compression, lower density, bigger volume, so compression test would stand to be ~ 82% of the stocker 11:1's 220... which comes to 180 PSI.
My cyls are 150 - 140 (30-40 PSI lower than theoretical calc).

Should I be concerned?

It's a 2.0L Laskey motor, Full-race manifold, stock AP1 cams, GT3076R, 15K miles on it, mapped to run 11.5:1 in boost / 15:1 cruise, smooth fuel & timing maps with nothing jagged in the maps. Car never ran irregularly, but never got the same mileage as when I was at 11:1 (I'd attributed this to the lower CR being less efficient). I'd added a couple of degrees of timing in cruise to try to offset the loss in CR, but never got aggressive with it (dynos around here can't hold steady state 60 MPH well enough to tune for MBT in that load band).

Please chime in on your setup & what kind of compression you see on compression tests:

Compression PSI / conditions
Engine Compression Ratio / cams if different than orig

Thanks,
Stanford

 

150 is about what i'd expect

 

Laskey block with a final 9.3:1 compression ratio currently.
I've been playing with the cam timing and recording the compression test results for the last week. The lowest I have seen is 162 psi, cold with 10 full cranks, butterfly wide open and fully charged battery. I decided on 10 full cranks after playing around with the compression gauge. Cranking less than 10 times results in lower values.

HTH

 

Have been running compression tests on this same motor I originated this thread with, but the motor has been rebuilt with a 2.2L crank CP 9.6:1 pistons and Cometic head gasket slightly thicker than stock to hit 9.4:1. Same cyl head nets the same "pattern" of variances in my compression readings with a motor we targeted 9.4:1 CR. (Reason for variances is likely slight differences in chamber volumes or cam lobe/phasing). Engine now has about 2K miles on it, does not "gas" the oil at all, does not burn oil, plugs look clean.

Cyls 1-4 are 187, 184, 181, 185

What's interesting is how much more "crisp" this motor is down low just driving around town & for spooling the GT3076R on Full-Race ramhorn manifold. Dyno plots show 400 RPM earlier spool / stronger boost curve, partly due to the stroke adding the displacement and partly due to compression bump from 9-ish/150 PSI cranking of the old motor to the new 9.4/185 PSI cranking. It's just amazing how much more responsive the motor is, and I think part of that is due to the 2.0L build having its compression ring seal fatigued by a load of bad gas (this was before I'd wired my CEL to light up when knock exceeded 1.85v).

The 2.2's really nice, even if it's been mega-sensitive to timing. From 6K-8K, it doesn't want more than 4 degrees / 14 PSI before it hits my 1.8v knock limit on 92 octane. My old 9:1 2.0L build cranked 145-150 PSI and wanted 12-ish degrees of timing at 14 PSI (1.8v knock) from 6K-9K RPM on 93 octane. Since I have E85 available here, I converted over to that (which helped spool & allows me to run 6 more degrees timing (10-11 total) in that same range at 14 PSI (50 more RWHP/TQ too, which is nice).

Point is, observing really conservative knock and running E85, I'm looking forward to good longevity and keeping that crisp throttle response around a good long time. Not going for aggressive dyno numbers - just going for years of service.