adrial

Anybody else find it odd that the trend seems to be that newly rebuilt engines (within 10k miles) have lower compression than people with 100k on their engines?

I just checked mine (engine hot), around 6-7k miles after the rebuild and I'm at 138-139 on cylinders #3 and #4, engine runs great...uses zero oil.

I suppose its possible the gauge just reads low. As a useless comparison, my brother's 914 engine tested at 130psi with the same gauge.

Same gauge also placed my engine at 135psi (tested cold this time) when I got the car around 70k miles, 4 years ago.

AL951

looks normal to me

Reagards,
AL

meanmaroon951

Run synthetic? Didnt break it in good enough??

adrial

meanmaroon951, Yes I run synthetic, it was broken in fine I think. few hundred miles on straight 30 weight nondeteregent, little bit more on 10w40 (standard dino oil), and then changed to synethic around 700 miles, then it went to the track.

AL951, Are you referring to my compression numbers or the tendency?
I agree on compression numbers, they look fine to me... a little low but that could be the gauge.
I was just wondering because it seemed like an odd tendency...

KLR

Are they the same across all four? The gauges are often incorrect, but if you are not getting a consistent reading across all four cylinders, then there may be an issue in the making. That said, high 130s is still OK. I got 145psi+ across all four at 114k miles (last time I checked). My motor has never been apart and has run on dino oil its whole life.

pieball

adrial who did your rebuild btw?

adrial

KLR,

I only did 1 and 2 (mistype in original post), 3 and 4 are more of a PITA to get to....I was just wondering where I was at. The engine runs great(uses no oil), so I am sure they are close. If they aren't, well I am damn well not about to take it apart again!! The two I tested were within 1psi, so that is good enough for me.

pieball,
I did all the assembly/dissassembly. I brought the head/block/crank etc to a machine shop for all the machine work (and head rebuild). It was a great learning experience.

MichelleJD

Mine tested at 120-121 across the board. Perfect for each cylinder. However, The engine had been sitting for a couple of hours since running and I had no way to hold the TB open. I was very happy with the consistency.

black944 turbo

This is due to Carbon build up on the pistons. That is why older engines will have higher compression. For comparison, my Volvo with 168,000 plus on it has higher compression by 15psi all cylinders than the book says it should. I need to check the porsche again but it was normal at 80k.

eniac

A few years ago mine was 142-144 with 110,000mi. I now have 120K on the car and was going to do another check soon as I have low vacuum but no intake leaks.

adrial

Thats what I thought initially .... but isn't the factory spec 140-150psi? Or is that just Rennlist hearsay?

shaheed

curious about this too, that's the range i've always thought is correct but then i've heard people give all kinds of conflicting results (over 150 etc)

David Floyd

Did you check the compression after a few miles on the engine ?

adrial

David,

I assume that was directed to me... and yes it was just tested at 7k miles since the rebuild with the engine hot (burn yourself on the intake manifold hot).

David Floyd

I ment did you check at like 100 miles, then you would have something to compare to, if you had 138-139 then and now, could be just the gauge.