what is good 911 compression

just had compression checked on my '88 Carrera:
1=165,2=170,3=170,4=170,5=170,6=160

Is this good?
Should I be worried about one cylinder being 10 lbs lower than 4 others?

If you are counting correctly, the #1 and #6 cylinders are catty-corner to one another. I have always wondered why these particular cylinders show a lower reading?

The figures seem good to me, but I'm no expert. Certainly the figures may be higher due to the additional carbon buildup in the cylinders themselves. I have just finished running Techron 20oz bottles through two consecutive tankfuls, putting the car through its paces for a minimum of two hour runs (heat+Techron=carbon breakdown). The car is now on jackstands and I will perform a valve job along with rotor swaps and other bits and pieces. I will again have a compression test and a leakdown, this time noting where the hiss is coming from on the car.

jw

John,

The general guidelines are that no cylinders be more than 10% from the mean, and with a mean of 167.5 psi, you are well within those guidelines! So, no, you don't have anything to worry about at all!

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Warren Hall
1973 911S Targa

The reply that Warren gave made me think of another question. If all cylinders were between 115 and 120, as in the case of my '77 930, can I assume that my numbers are Ok for my engine.

Beagle,

Those don't sound bad at all for a 6.5:1 compression engine, and that is what the 3.0 turbos had, right?

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Warren Hall
1973 911S Targa

I just tested my 1988 Targa. Here are the results:

1 = 155
2 = 150
3 = 150
4 = 145
5 = 160
6 = 155

AVG = 152.5

I think that this is with spec. I checked #4 twice with the same results. Am I right?

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E. William Reinecke
1988 Carrera Targa