Did A Compression Test

copper_gst · 04-29-2004

I did a compression test yesterday and this is what I found. I still have boost leaks because the injectors aren't seating right so I don't know if that would effect the test or not. I hope it would, but here are the numbers. The #1 cylinder 160 #3 cylinder 180 #2 cylinder 150 #4 cylinder 190. I Would appreciate all the help I could get on this, the car is also heating up still. I'm gonna put a new thermostat in it and see if that helps. Please let me know what you think.

thanks

curtis

**v8klla** · 04-29-2004

Well do the injectors go into the combustion chamber or into the intake manifold/head right before? If the injectors are in the combustion chamber that would adversely affect your numbers if they are leaking...

Chris

AJ · 04-30-2004

Might want to try a leak down test and try to narrow some things down.

**1ViciousGSX** · 04-30-2004

How many revolutions did you crank it over during each test? Wet or dry test? That is a pretty big difference between cylinders.

SlowWhite · 04-30-2004

time for MCCC?

-Brian

john · 04-30-2004

Was the car warned up when you did it? Two of the cylinders are too high (180 and 190). I believe the stock compression in a 2g cannot exceed 178 unless you have excessive carbon build-up or you did the test wrong. Retake the test after really beating on the car so you know it is warmed up. If the numbers are still high, clean your cumbustion chambers with MCCC like Brian said.

Raptor · 04-30-2004

The higher compression isn't surprising, the head was milled >.010" and the valves are larger than stock, they are flat on the bottom instead of having the small dish like the factory valves. Both of those things will contribute to a little higher compression numbers. The leakdown test like allan mentioned is really the next thing to do to see where the varience in coming from.

Injector seals don't cause compression leaks, they are inside the intake runner and behind the valve so they have no effect on compression. They can leak boost like you found of course.

The last thing is to obviously make sure you are using an accurate compression tester. Lately we have seen some really bad numbers come from cars that were fine due to people using junk testers. Use an equal number of revolutins, throttle blade open etc.

**Shane@DBPerformance** · 04-30-2004

Isn't it 9.0:1 compression also?

The car was acting like some other cars that we have dynoed that had blown headgaskets. They have ok compression and can run all day under normal driving conditions, but as soon as you put a lot of boost to it the coolant temps start skyrocketing.

john · 04-30-2004

Quote:

Originally posted by Raptor@Apr 30 2004, 11:51 AM
The last thing is to obviously make sure you are using an accurate compression tester. Lately we have seen some really bad numbers come from cars that were fine due to people using junk testers. Use an equal number of revolutins, throttle blade open etc.

Mine is fine. We checked it on ghettostyle's car. Iceman just doesn't know how to use one :stick: .

copper_gst · 05-01-2004

yeah, it's 9.0:1 The car was warmed up, but I'll get another tester and do it again. I've never done a leakdown test either so some info on that might be helpful. I'm going to fix the injectors either tomarrow or on my day off. I'll keep you posted. Thanks for the help, any more is greatly appreciated.

**JET** · 05-01-2004

The most common is to turn the car over 7 times when doing a compression test. Pull the MPI fuse and all the plug wires before hand. Your fuel injectors also will not make a difference, they are outside of the combustion chamber.

Enes · 05-01-2004

I heard its 4 times not 7 times?

-E

**1ViciousGSX** · 05-01-2004

Between 5 & 10 is a good number as long you do the same number of revolutions per cylinder. I like 5 times each.

Raptor · 05-01-2004

We always go 7. Like Mike said, between 5-10 is fine, but it is worth it to choose a number and stick to it for repeatability and comparison sake. I may start hitting the engine with the IR temp gun to try and keep testing at the same general temp also for the same reason. It is always good to develop a good solid method and stick by it whenever possible.

05-25-2004

I am more concerned about the spread from 190-150 (difference of 40) I know that the spec book states that the range between cylander should not be um um (ok i forgot the number off hand) but you get the idea. Obviously we are seeing a HIGH number on two cylinders. I would recommend running the test with a diffrenent test as other people have said (i have one if you need to borrow it let me know) make sure you are getting the tester sealed tight and run it the 5-10 times. (dont forget to unplug the injectors and also to take out the mpi fuse it would be a huge mess)

Good luck dont forget WOT

Let me know if you have any other questions

-Tim

Raptor · 05-26-2004

Thanks Tim, didn't we have all this covered around a month ago? Did you add something we didn't cover and I am just not seeing it? If you are really bored you can go back a few more months and answer several other questions that have already been covered as well.

PSI2HI · 05-26-2004

It still runs and thats good enough.

Check your lifters they are usually a good cause of low compression, had those be a problem many times. Second is usually leaky valves.

Leave the compression tester in your toolbox until the car starts to run shitty. All that compression testeris gonna do for you is make you worry about your motor.

Nick

Enes · 05-26-2004

he just had the head rebuilt.

-E

Raptor · 05-26-2004

Again, this thread was done a month ago

The head gasket is being replaced next week.

05-29-2004

Well if you fix the problem maybe you should say so that way people dont keep trying to help. And it always helps to chew ppl out makes them feel like adding their input.

-Tim