Nestle12

I did search, according to what everyone else seems to say my motor has extremely low compression. Here's the deal:

The car runs perfect, no cold or hot start issues, the Engine was rebuilt last year, I just pulled the motor out to clean up the engine bay and fix an annoying oil leak. Since the motor is now sitting on the garage floor I did a compression test (snap on unit). It only has 55psi front and back!!! I tried with the valve out of the compression tester and it spikes 50psi on all 6 seals wtf?? (also tried upper and lower hole still nothing changed, and yes I had a plug still in the 2nd hole while testing).

It has a single GT35R on it, pulled that off, exhaust wheel is mint, pulled the manifold off and the rotors look clean all apex seals are intact and look great. The motor sounds like it is strong when spinning over with plugs out (old motor had bad seals, so I know the sound of death!).

I thought it maybe a bad tester, did a quick check on a buddies sr and it worked fine 154psi...

now I'm worried!!!!!!!

misterstyx69

iTrader: (142)

When you did the compression test,did you have the throttle cracked all the way open?,good battery?

Nestle12

I have the intake manifold pulled off (upper section) so its wide open, I just hooked up a new diesel battery to it and it went up a tad, but still only around 55psi. With the schrader valve in it wont go above 55psi. It hits 50 1st pulse and just stays there.

I wouldnt think the car would even run at that low of a number? But it runs perfect, and it sounds sharp and crisp (straight pipe 3 1/2" no cat).

The weird part is the 50psi is dead nuts on all pulse's......

misterstyx69

iTrader: (142)

I think you are OK!
look at this!:
Compression test using a piston engine tester :
1)


note battery strength. A weak battery will yield low compression results.
2)


Remove both lower plugs and wires.
3)


remove EGI fuse from engine fusebox.
4)


have a friend floor the accelerator pedal, opening the throttle for more airflow
5)


insert your tester into the leading hole
6)


hold the valve on the side of the tester open
7)


have your friend crank the car over for 5+ seconds.
8)


observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range.
9)


let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment.
10)


repeat for opposite rotor. Note difference in overall compression between rotors, which should be no more than 20psi max.

dwb87

iTrader: (22)

You say the engine was built just last year... Do you even have any miles on it yet? If you have very very low mileage, or no mileage at all, it would make sense that you would have low compression. Newly built engines are pretty low to begin with. No need to freak out. Time to get it running and baby it through the break-in period.

RotaryEvolution

iTrader: (30)

compression is relative to cranking speed. is your starter junk? i bet it is.

RK53

As others have stated, cranking speed is a critical factor in compression testing. Another thing to consider is how dry are the seals when you're testing? Dropping a little oil in the spark hole, cranking it around a few times and retesting might give you dramatically different results.

If you were to truly have low compression, starting would be an issue. Since you say it starts hot and cold fine the engine is probably ok.

Russ

Nestle12

It only has 10k on the motor, Yes its bone dry, I'll try a drop of oil. the numbers with the valve in is what scares me. I bought a cheapo tester today and tried it, front hit 75 with full charge battery, rear 70. I have an extra starter too, I'll swap it on and give it ago!

I originally thought the motor received new rotor housings when it was rebuilt, but now I noticed that they were just painted silver as the paint is starting to flake in a couple spots. The cast plates arnt flaking still gloss black..........

Nestle12

This part makes me feel a bit better, it bounces even 50psi on all hits front or back.

misterstyx69

iTrader: (142)

I saw that.That is why I tossed all the info up.Just so you could see how it was done to get that reading.
Makes ya feel warm and fuzzy now,huh?

Nestle12

Update, put a couple drops of oil in the plug hole, now has 100psi pulse's on front & 90 on the rear!

RK53

Don't be afraid to oil it up pretty well. A 1/2 to 1 tea-spoon wouldn't be too much oil. I'd throw a little in each lobe space. Especially if like you say it's bone dry. Not good to crank it that way either.

I'll bet you'll see a big improvement in readings.

Russ

les mazolla

Below 90 ? Does it mess up anything when it blows ? Thanks