30psi variance?

[Indecisive]

hey guys, the motor I'm looking at has got a 30psi variance from highest to lowest.

The importer, JDM Source, gave me these numbers.

> Cylinder 1: 170 psi> Cylinder 2: 180 psi> Cylinder 3: 170 psi> Cylinder 4: 150 psi

What do you guys think? Should I wait and have them try to find me another motorset with better compression or since all the numbers are so high, would I be okay even with that much of a variance?

[c-rad]

14psi variance is the limit. Stay away from that motor. Also, how the heck did they get 180 psi in cylinder #2? That's a little high for a stock compression CA.

[Indecisive]

that's what I was thinking as well.

stock compression on a warm motor is 172 isn't it?

[c-rad]

that's what I was thinking as well.

stock compression on a warm motor is 172 isn't it?

Yes...on a freshly rebuilt motor warmed up. Most of the motors you find will be in the upper 150s to low 160s.

[Indecisive]

I'm pretty new to the mechanics side of cars still. So can you tell me basically how much of a rebuild would I need to get the engine up and running properly?

Would it need to be torn town to a bare block and have all gaskets and seals replaced and put back together or is it something like just redoing the headgasket and I'm good to go?

[c-rad]

Low compression numbers are usually the result of worn piston rings. You would need a new headgasket anyway and since the motor is apart, may as well do the bottom end bearings. So yeah, you are looking at a total teardown and rebuild. The labor will cost more than the parts provided it's just the rings that are worn.

[dattodude]

My engine had 185 in 3 of the 4 cylinders (fourth had 100psi). Of course it was time for a rebuild.

It's possible the carbon build up in the upper cylinder was 'raising the compression, but all the same.. thought I'd share for the record :-)

[float_6969]

Yea, I remember reading about someone's dad having a volvo that had better than stock compression at like 200K miles. It was so carbon fouled it was raising the compression. It was also pinging like mad...

[r34 gtr]

my dad's 89 bmw 325i has 220k on the clock and 210psi in each cylinder. its supposed to be 180 new. it runs like a dream. carbon buildup FTW!

my CA had 175 in all cylinders when i got it, with 22k on the clock. i'd say its easily possible if the engine is in good shape.

- Tim

edit: does anyone know why its always the #4 cylinder that goes? its never at the front of the engine...

[SeVa-S13]

The theory of forward-facing plenums is that the rear 1 or 2 cylinders receive the most air due to the nature of forced induction. More air than average = lean, lean = pinging, pinging kills rings.

[ccasey645]

The theory of forward-facing plenums is that the rear 1 or 2 cylinders receive the most air due to the nature of forced induction. More air than average = lean, lean = pinging, pinging kills rings.

Thats why im a big fan of the rb series motors intake manifold design (having the throttle body on the "top" for the lack of better terminology). But im sure it still crams some cylinders more than others.

[SeVa-S13]

It does; 3 & 4. As an RB owner I did kind of like the idea, but the piping routing and clearance issues just aren't worth it.

Plus, that's why you always get your injectors cleaned and tested and put the highest flowing ones in the potential problem cylinders.