Bad Compression

[mac 108]

I have a 92 turbo AWD eagle with 150, 150, 120, 150 on the compression. I started at about 10 psi and I was running about 11 psi with a 15.5 ET. Using a datalogger and a Gtech, I increased the boost, and shaved about .3 tenths off of my ET to get to a 15.2. I was tuned for about 16-17 psi with no knock and made almost no difference. Timing and IDCs are normal. 1 Psi should be good for about 10 hp I have read, and I have added 5 or 6 psi since the beginning with almost no results. I have a lot of blowby, is it the poor compression that is killing my times?

 

[majik2k5]

10HP per psi is probably going to be on a motor that's built up with a big turbo and good supporting mods.

If you're increasing the boost and not seeing any difference, check for boost leaks. Were you actually getting these times from the track? Because if you are, and you're running mid 15's.... then something is extremely wrong considering you're AWD.

 

[mac 108]

No boost leaks, checked multiple times and all vaccuum lines that can be have been capped.

Current mods include a 16g Evo GT, Evo III exhaust and O2 manifolds, full 3 inch exhaust, no cat, 255 walbro, 650 cc injectors, AFPR, 2g mas, K&N filter, dejon intake pipe

at the track i ran a 15.5 with a 2.7 60' time. I could have stalled it more

the Gtech is consistently off, it has been track tested, so its numbers are correct

 

[oldman]

at the track i ran a 15.5 with a 2.7 60' time. I could have stalled it more

2.7 is cosidered bad even for a FWD, it's time to work on your driving skill, with the mods you listed you should be at least in the 13's if not high 12's.

 

[mac 108]

it is an automatic, i did cut a better 2.1 60' with more stall later on that night

 

[majik2k5]

There's no reason for you to be running 15's though. Auto or not. We need some more input on this situation. Does the tranny feel any different? Did anything feel awkward when you raced?

 

[steve]

The factory limit between cylinders is 14 psi and you have 30.
Your also almost to the low limit on compression in cyl 3.

If you really want to race the car you might want to start thinking about a rebuild.

Steve

 

[GTM]

The factory limit between cylinders is 14 psi and you have 30.
Your also almost to the low limit on compression in cyl 3.

If you really want to race the car you might want to start thinging about a rebuild.

Steve

If I may, industry standard for a gasoline engine is usually considered to be 10% variation between cylrs.

It is my opinion that this car should not be subjected to any further abuse until the compression is brought within specs. If it's burned valves, piston and cylinder galling or bad rings nothing will improve by taking it out and playing street racer. If this has been a consistant reading from several tests then something should be done before the engine is ruined. It is common place for a mechanic to take 1 complete set of readings and then go back and repeat any that are suspiciously low. The reasons for this is it's common place for deposits from plug removal or dirt in the plug well to fall off and get trapped under a valve. Sometimes just free running the starter with the plugs out will clear it and yet another test before reporting it as bad.

The choice is yours on how to prolong or shorten it's life.

Cheers,
GTM

 

[mac 108]

I have done three compression tests in about 3 or 4 weeks, and the result is always the same. I am getting a lot of blow by through the oil cap.

 

[GTM]

I have done three compression tests in about 3 or 4 weeks, and the result is always the same. I am getting a lot of blow by through the oil cap.

You probably were hoping that close encounters of a 3rd kind were going to change the rules of physics. Unfortunately it ain't gonna happen. I've no problem with being wrong. Chances are that the piston and rings are history, then the question is do you bead hone the cylr, use a good used std piston that you have shot peened a couple thou and stuff it back together.

These are your choices, the procedure is proved.

Cheers,
GTM