Compression test onmy G/F's motor!

[boost_boy]

Well, since I volunteered to pick-up ca18det_boy (Aaron) from the airport at 10 this evening, I got bored and decided to give the car a compresion test. On a cold engine, cylinder #1 gave me 160psi (not bad, right), cylinder #2 gave 90psi (ouch, wtf), cylinder #3 gave 145psi, and cylinder #5 gave me 145psi. So I put some oil in #2 and the compression went up to 100psi. Si I decided to put the new spark plugs in and started the car up. It ran rough for a few seconds bnecause I never disconnected the main injector harness which cause theinjectors to spray while checking compression, fludding the cylinders. Finally, it smoothed-out! I watch the vacuum return to 20hg at 800rpm, but I was looking for it to be lower because of a possible broken ring-land or burned fire ring. After the engine hit normal operating temperatures, I did another compression test and all 4 cylinders were sitting smack at 150psi.

All the old spark plugs looked better than any that I've seen in a stock CA18DET from japan (I'll add a pic of them later). The spark plugs that were in there are BCPR6E-11 and I think that this thing is CA18DE plug or something from an SR20. Someone please confirm this as I don't have the time to research right now. The plugs I'm using now are NGK PFR5G-11. Any comments on the actions of this motor would be greatly appreciated. I know motors, but this just spooked me the fook out. Needless to say, the engine idles and revs just fine!

Dee

[gani]

you may need piston rings in the next couple of month cozwhenyou did the test on the motor when cold the rings were not set in but after warming up they expanded thus explainingthe good compresion after warmup. do a leak down test to be really sure but i wouldnt worry too much. just my 2 cents

[Nismo1182]

Im using NGK BCPR7ES-11.

[gani]

oh about the plugs im running iridiums soi dontknow about the normal plugs.

[float_6969]

Dee, how many times did you get 90psi on that cylnder? I always check them 3 times a peice. So I'll check 1-4, and then repeat it 2 more times, just to get a spread and then I'll find the mean of my results. That way if you did something accidentally, the chances of you repeating it on the same cylnder 3 times would be slim. Plus the fact that adding the oil only bumped it 10psi tells me it's not the rings. That is more like the change in volume due to the oil taking up more space in the cylnder. I would retest and see what you get. The reason that I do this is because I was doing a compression test on one of my other 240's that I had with the KA motor in it. The first time I tested it I got something like 150-150-85-150. I was obviously freaking out. So taking into account the fact that I'm a dumbass, I decided to check it again. 2nd time I got 150 all across the board. 3rd time, same thing. The only thing I can figure is that I either didn't get it threaded in well on that cylnder, or I had something against the release valve and so it wasn't holding pressure. Anyway, I'd retest and see what happens.

[PacManVR4]

SHould I be happy i got over 160 on a cold motor?

[float_6969]

Darn all of you and your rings!

[PacManVR4]

He He ring boy, Im hoping lol.

[boost_boy]

Quote »SHould I be happy i got over 160 on a cold motor?[/quote] You're okay!

[r34 gtr]

im so envious

- tim

[Myetball]

I'm thinking that since you got good compression after the warmup that the rings are fine. The only thing I can think of would be an excessivly dirty ring groove. When cold and under no load the ring may be not be expanding properly. Once you warm it up and run it with some load everything frees up and runs normal. Of course the only way to know for sure is to tear it down and with normal compression at operating temperture there really isn't any reason to do that.

[boost_boy]

Quote »and with normal compression at operating temperture there really isn't any reason to do that.[/quote] You think like I think and that's why I wasn't gonna touch it, anyway. Quote »Dee, how many times did you get 90psi on that cylnder?[/quote] I got it like 3 times and when I added oil to the cylinder, it only went up a couple of points. I had no particular reason to check it; just felt like doing since I hadn't done it for some years. Like I said in another post, I took ca18det_boy and his friend out for a ride today and the car performed showed-off. The vacuum sits at 20hg when idling and I've improved the throttle response of the car by doing some tuning on a section of my system in which I used to completely avoid. And it's definitely a section I can contribute to alot minor performance woes. It sounds good and looks even better and can't wait to get it back on the dyno with that same 15psi setting.

Dee

[float_6969]

One day, when I get my car unsuck from the snow, and I have the money, I'll be fast too!