My setup consists of je pistons 20 over, eagle rods, ported and polished head, stock valves cams.

I noticed my vacuum dropping at idle shortly after my 440 install. I ran a compression test today and heres what I got:
All four cylinders running 130lbs +/- 2 lbs. As per chiltons I dropped about a cap full of oil in the plug holes and re-tested. All four cylinders went to 155lbs. I'm stressing because I'm under the impression that they are supposed to be somewhere around 180-200lbs after checking previous posts. My mechanic informed me that it was perfectly fine cause they are all the same. He told me that my engine is probably running rich which will cause vacuum to drop. He suggested I corect it soon cause it can cause the rings to lose a good seal.

My engine management is run by the emanage. My thoughts are that I need to sell that piece of crap and get a squirter (MS n S)running. would you guys agree with the analysis rather than engine trouble such as crank bearings or something with the lower block?

Thanks a lot in advance, I really appreciate it. I've been really bothered by this for a few days now.

Did you hold the throttle open while testing?

Can't tell you what your compression test should read unless you tell us what the compression ratio of your piston/rod combination is.

With a turbo kit, I'd be willing to bet he's running somewhere in the 8:1 range. Might not be that bad, but my questions would be the same about testing at WOT and then to ask if the engine was hot or not. Remember, forged pistons will expand as they approach operating temperature. If the engine was not tested at temp, you would have some leakage imo.

Shit, I forgot the WOT part. I guess I don't see why that makes a difference. The engine was warm. I had just driven it for about 30 minutes. I think the compression should be 8.6:1 with the pistons and rods. I guess I can try it again with WOT and s what it reads. Do you think it will make the numbers higher? For the most part I trust my mechanic for anything other than electronics. He's done two 420a rebuilds but he works primarily on viper engines superchargers and rebuilds. So engine wise he knows his shit, but electronics, I just don't think he's up-to-date. the last thing I want now is to have my engine pulled again. I don't really se how I could have blown anything cause I haven't had a detonation since I first got it rebuilt almost 4 or 5 years ago. This all came up after I put the 440's on.

I was doing a pass and took the car to redline in 3rd while watching my egt's and a/f closely at about 16psi, was running awsome, when I shifted to 4th, it felt very boged down like it was running rich, then the elbow off my turbo that connects to the i/c piping blew off. I don't think it blew anything though. That's I think when I really started noticing the car running weird.

Originally posted by xceler8
Shit, I forgot the WOT part. I guess I don't see why that makes a difference. The engine was warm. I had just driven it for about 30 minutes.

Good call on the engine being warmed up.

You need to floor the gas pedal, because you are trying to build as much air pressure in the cylinder as possible during the compression test. I figure that going from 9.6:1 -> 8.6:1CR is about a 10% difference and then remember that most people pull down 180-200psi on stock compression. If you saw 10% lower numbers than, say, 180psi, you'd be right around 160psi. Maybe your numbers aren't that bad.

This is all just speculative, imo, but something to think about. I don't know that 155-160psi on 8.6:1CR isn'y really that bad. :shrug

I checked compression on my 8.8:1's after about 300 miles of driving and my numbers were 180-180-175-175 with the engine cold and not at WOT. Those numbers seem low, but I'm not sure so don't take me too seriously.

I get 150 all day long on my 8.6:1's(I don't use the WOT theory when I do my compression tests). I truly beat the shit out of my engine as well. 15 psi (10 if its wet out), open track day's, lots of autox's (which are harder on your car than a 13 second pull down any drag strip). If your getting 150 ish then I would say your ok. 130 or lower then you might want to look into it.

that does not really seem to be the problem though, you said you were loosing vacume after you changed injectors. Try doing a pressure test and see if one of your injector o rings is leaking. could be as simple as that.

Originally posted by RxR_Eclipse
I don't use the WOT theory when I do my compression tests

It's not a theory, it just happens to be that our motor can suck a lot of air through the IAC orfice that it doesn't create much drawback on the pistons.

Try not opening the throttle on a 240sx doing a comp. test.

dunno about a 240, I have a eclipse. I have never done a compression test with the throttle open, guess its just my method then. Ill try it your way and see if my compression goes up *shrug*.

I always did the comp test with the throttle closed. I tried it last night on my cougar and there was a significant difference. Of course, it's carbed.

cyl - no throttle - WOT

1 - 190 - 210
2 - 170 - 185
3 - 175 - 190
4 - NA - 40

I blew the head gasket out the side of #4, which I knew, but I figured since I was taking it apart, I'd test the WOT compression test. I was a little disappointed with #2. I didn't even mess with the left bank, as the battery was getting weak. I know #1 is correct, but I don't remember if the others were exactly that, but that's close. I guess I may actually be 'freshening up' the motor after the last race of this season.

That is about a 9.31% increase on average. This would leave me to believe that my car should get about 163/cyl instead of the 150 I usually get.

well, i just did comp test on my eclipse with 8.8:1.
got 190 - 190 - 185 - 190, bout 500 miles on the engine with loose hastings rings. and lots of boosting since mile 1.

Originally posted by RxR_Eclipse
That is about a 9.31% increase on average. This would leave me to believe that my car should get about 163/cyl instead of the 150 I usually get.

Try it and see because quite a bit of air can get by the IAC, where as on my cougar, there's no bypass.

It may raise the numbers. There's only one way to find out.