Compression Test Result ?'s

Alpine TSi · 08-19-2004

Recently I did a compression test and got 155's across the board. About 3K ago I had the head redone and valve seals replaced. I am not sure as to what all was done besides some healthy port work and stock valvetrain, Mike at QPR did it for me.

Now what boggles me is that the shortblock has 172K on it with no signs of being rebuilt, I am nearly 100% sure that it has never been touched. Normally I could just brush all this off as someone before me taking good care of the car and it is still holding up, even after 172K miles.

But the thing that bothers me about it all, is that if my hood wasn't shut while I made a full boost pull, I would launch the dipstick into orbit. Under approximately 20 psi I get nasty blowby coming from anywhere it can(valve cover breather, dip stick, valve cover, etc..). And then comes the oil spray from the dipstick. It is a nearly brand new stick too. I had to zip tie the thing down just to keep it from flying out(crimping the tube didn't work either).

I don't understand that how with nearly perfect compression why I am encountering so much blowby.

Any ideas?

john · 08-19-2004

Did you do the compression test on a very warm engine? I beat on it and then do the test to make sure it is warm. I would try another gauge also. My car (stock block) clocked 170 across the board on Elites compression gauge (dynofest last year) and high 150's on my snap on gauge. Some gauges read higher than others. High compression can also be due to excessive amounts of carbon in the combustion chambers. I blew my dipstick out at ~20 pounds on the big 16g and do not now after crimping it with more boost and a larger turbo.

Alpine TSi · 08-19-2004

Yeah, warm engine. I am not so concerned about the number itself, but all the numbers being close to eachother. It is kind of like everyones rulers having different sized inches on them. I have had the test done with a different tester, which tested higher.

Raptor · 08-19-2004

Check your PCV valve. If it is bad (highly likely) you are boosting your crankcase

Not really ideal if ya know what I mean. Anyway, you can plug the port on the intake, and run with the VC port open and see if you don't kill your flying dipstick issues. That is what it sounds like to me.

Alpine TSi · 08-20-2004

If it is found that the PCV is bad, should I just replace it? Or just leave it as you mentioned, and add a catch can for that and the VC breather too?

john · 08-20-2004

Just replace it. They are cheap and a part of maintenence. I believe you can check it by pulling it off and feeling for a vaccum at idle. If there is vaccum, it is fine.

Raptor · 08-21-2004

Actually that won't tell you if it is stuck open. You can pull any line in the intake track and find vacuum at idle. Just check it like I said earlier and deal with it from there. Should be pretty easy. Personally, I don't run a PCV ever just because I don't like the idea of it potentially boosting the crankcase even once. I used to have an electric vacuum pump hooked up instead, that worked very well, but now plans have changed a bit. I will always have some form of vacuum to evacuate crankcase pressure and it will never be a PCV relying on engine vacuum. That system is stupid in a boosted vehicle anyway, as soon as you are building any boost, that system is closed and that is when the pressure needs to be evacuated. Not a very effective method IMO.

So, you can decide if you want to keep it now after all my rambling