2.7 compression

[healeykit]

Does 120-125 across all cylinders seem low for a 2.7 from a 77 911s?

[patz]

If they are consistent, it's a runner. But 140 is what I would consider as "good".

[Targalid]

Wayne Dempsey's book on rebuilding Porsche 911 engines is a good source on this topic. Look on pages 14-15 where he discusses this very topic. If the 2.7 is fitted with hotter cams, these readings may mean a good engine. If fitted with standard 2.7 cams, 120 is low. Also depends on how the test was done. The numbers are consistent which is good. Did you do the test yourself? Was the throttle wide open during the test? Did you add a tablespoon of motor oil to each cylinder and test again? Is this engine in Ontario or in Denver? In Denver, 125 psi is not bad. In Ontario, not so good.

[healeykit]

Yes in Ontario. Described as stock. Compression results are from a bench test by an experienced mechanic completed about 6 years ago before the motor was placed in storage.

Leak down numbers were 8-12% with one cylinder at 20%.

[Flieger]

If you assume 14.5psi atmospheric pressure then you should get 123psi gage with a 9.5:1 compression ratio and 100% VE. Your numbers sound good to me.

[cgarr]

You can change those numbers a lot by timing your cams different in a 2.7 too

[Matt Monson]

Am I the only one concerned by the leakdown?

[JohnJL]

I wouldnt place much faith in those numbers. Thats a few big gaps, a lot of time to pass and variables. Pretty leaky too.

What are you looking at and what are you trying to achieve?

Also here in Ontario....

[manbridge 74]

My first 2.7 made 160-170 at 8500 ft. CIS with S cams. No idea on internals but it was a strong runner.

[healeykit]

It's a basically complete motor but with carbs. I'm looking for something to drop in and run.

[Jcslocum]

Here is a data point for you:



This was done on a '77 - 2.7 with 100K miles in storage for about the same amount of time, maybe a bit longer.

How was the test done?? All plugs out? Throttle wide open? strong battery? cranked until the needle would no longer rise?

On a cold engine that has been sitting it's a bit if a crap shoot with these tests.

[healeykit]

Hi Jon, thanks for your post, if this motor showed those numbers it would be in the back of my truck already. It's because the comp seems low and the leakdown seems high that I'm concerned.

The guy who did the testing is a legendary porsche guy (heck he could find 6 year old detailed records in ten minutes) so my guess is his numbers are accurate.

[javadog]

Originally Posted by Flieger

If you assume 14.5psi atmospheric pressure then you should get 123psi gage with a 9.5:1 compression ratio and 100% VE. Your numbers sound good to me.

That's actually low for that compression ratio. Should be much higher.

A '77 didn't have 9.5:1, though. It had 8.5:1. His numbers are low, even for that compression ratio.

The leakdown numbers are worse.

If the test was done properly, that motor could use a rebuild.

JR