Oilslick964

What is the acceptable range for compression on my 1986 951. I used to know, but I get mixed-up between numbers for a 928, 911, 944 and a 951. I just slipped a couple of teeth on mine and I'm hoping and praying that it's ok! Where should it be?

Mighty Shilling

Good luck man! hope things work alright and no valves be dead... sorry I can't be of help with compression numbers, just gonna wish the best for ya

iloveporsches

IIRC (it's been about 2 years since I did my own compression tests) you're looking for numbers around 160.

Mighty Shilling

in a 951? isn't the compression lower cuz it's a turbo?

Oilslick964

I was afraid of that. I've got at or about 135 across all 4. I was hoping that, since they were so uniform, that it was ok. Just my luck.

jaycm

it's ok. if the compression of each cylinder is within 15% of each other i consider this normal wear.
if it's not burning oil or other low compression side effects, i'd drive it like i stole it.

Mighty Shilling

Oilslick, if it's a 951, you still have hope maybe. 951's have lower compression pistons, and therefore these may still be good... there may still be life in that engine...the fact that they are uniform is a good thing, but do they hold the pressure? what's the leakdown?

Oilslick964

I didn't have them do a leakdown. They just called back and said they think it is ok. There is no valve noise and it seems to run great. WHEW! I think I may have dodged a major bullet, here. They said when the last person did the timing belt, they did not tighten the nut that holds the tensioner in place and when it got loose enough, the belt just slipped 2 teeth, maybe 3. He said there is no evidence that the valves are damaged and the 135 across, is pretty common for a 951 that is 20 yrs old and has 100k miles. YeeHaw! My day just got a lot better!

MM951

135psi is about 7.5:1 compression....from what I recall..dunno if thats what a 951 is

My conquest is 7:1 and gets about 130psi on a good day

Oilslick964

Oh yeah, today...I feel...like the luckiest man...on the face of the earth....

Hey Mike- I've always liked those Conquests. I remember, back in '87 I had an MR2 that I thought was the shiznit and I could never keep up with the Conquests. What kind of real performance does your car have? Looks like you have some mods. What were the stock HP/Tourqe #'s on those and what do you have now? What about reliability?

CurlyDE

I checked my 951 about a month ago and got mid to low 140s across the board (I do not remember all of the numbers, but the lowest was 142 and the highest was 145). My mechanic said that was what I wanted to see ...

On a side note, I checked my daily driver this past weekend (prompted by engine light showing a misfire on number 3 cylinder) and got 215, 220, 160, 220 ... after getting myself worked up about it, I decided to check / adjust the valve clearances ... 240 across the board after that.

M758

I ran a check on my 944 NA motor. It came to 138 to 140 for all 4 cylinders. I did not worry. Not really sure if that is high or low, but they are quite uniform. The motor made power however and I am not sure if I trusted the absolute value on the gauge. I did like the uniformity however.

iloveporsches

So is uniformity more important than the actual results? Not sure how accurate relatively cheap guages are going to be from one to another anyway.

Jakerx

what would the psi be for my 89 n.a? isn't the compression ration 11:1? or is it something else?

Zero10

I presume that's not from a 944. 240psi would be nearly unheard of on a 944.
Then again, our engine lights don't show a misfire on the #3 cylinder either.

Here's a general rule of thumb for 944 motors.
180+ Great
150+ Good
130+ Getting pretty worn.
-130 time to rebuild

That's the guide I follow
For a 951, I think it's more like
150+ Great
140+ Good
125+ Getting worn
-125 time to rebuild

However, a lot of that is strictly personal opinion.

For a comparison, The results from my previous compression test are as follows:
1: 96
2: 91
3: 105
4: 90

And, my car still runs, drives and spanks a few civics here and there.