engine compression reading
 

Wondering if someone know what the engine cylinder compression is suppose to be for 3.2l US spec engine?
I have 100 to 105 PSI on all cylinders with 7 to 8% leak down. Is this normal or too low of compression? My 2.7 motor is reading 150PSI in all cylinders. Thanks.

I think wayne's book says anything within 10% on compression and up to 10-15% leakdown is ok.

Slim, something isn't right. Did you do your compression test with the engine warmed up and throttle wide open? You should be reading between 180-200lbs per cylinder! The fact that all the cylinders are reading close to each other makes me think the gauge is bad or you weren't reading it right if the engine was warmed up.

When I tested my 3.5/6, my compression #'s were between 105 and 103, excep for 2 dead cylinders. I posted the same question and it was mentioned that as long as they are all uniform, the numbers do not really matter.

Also, it was mentioned that the bigger the p/c's, the lower the #'s become.

When I first read the readings, I questioned my gauge. So I borrowed one from my mechanic and read identical. The motor was warm but did not check with throttle wide open. Does that make a difference? Also, I pulled all the spark plugs before checking each cylinder. Everyone I talk to so far says the reading is too low but cannot find any spec to tell me it is so. I even asked local porsche dealer mechanics and no real answer.
-steve

Here are the readings from my 3.2 that I am now rebuilding:

#1: Compression 145, leakdown 80%
#2: Compression 180, leakdown 8%
#3: Compression 180, leakdown 6%
#4: Compression 190, leakdown 2%
#5: Compression 60, leakdown 100%
#6: Compression 205, leakdown 8%

The numbers that I remember seeing so far for 3.2L cars run 165-200.

Is your car stock? different cams will change the reading.

My mechanic just did a compression test last week on my 84 carrera with 120,000 miles. Compression ranged from 190 to 195 with a 3-4% leakdown.
Hope that helps.

Throttle should be wide open for compression test.

Peter

yeah, if throttle is closed then little air gets into cylinders = low compression.

It doesn't matter really...readings just get more accurate when you do it with open throttle.

Thank you everyone for the help. Once I get to bottom of this issue, I will post what I learn from Porsche specialist.

To my understanding,

Cylinder Pressure is a function of compression ratio and Camshaft.
meaning exact engines with radically different cam timing will show different compression gauge readings.

years ago when gasoline started becoming crap the guys with the high lift/big overlap cams and high compression ratios had to install a Crane or Isky, etc cam that detuned the compression ratio.. or do a detuned lower comp. piston swap......Ron