1-210
2-210
3-210
4-211
5-215
6-211

These were my compression numbers yesterday on my 98 Max with 122K. I posted this in the fourth gen section but I want some of your opinions as well. Are these compression numbers/mileage ok to boost my Maxima?

*When checking the compression I did every cylinder twice for accuracy, and while testing I had all of the plugs out and the throttle hung wide open. Thanks.

Carson

 

That's pretty good. I think specs should be in the 185 range, but it varies sometimes with different compression testers/methods. But the consistency is very good. As long as there isn't too much variation between the cylinders, you're ok. I'd say boost away.

 

Those numbers are on the high side, indicating possible carbon buildup in the combustion chamber. That is cause for some concern, since carbon buildup can give rise to glowing hot spots that cause preignition when boosting. If I were you, I'd try some method of decarburizing the combustion chamber and see if you can bring the compression numbers down some. It's good that the compression is pretty close from one cylinder to the next, though.

 

Any recomendations on how to decarbonize? The car does not sit idle for days on end...I drive it pretty much every day, I always use 93 octane gas, and when I do dive I tend to have a heavy foot...and I also use BG44K every once in a while....if it make any difference we checked the compression on my friends MR2 right after my car and he was getting the same numbers (around 210psi) so maybe the tester reads high?

 

It may very well be that your compression tester reads high. Do you know somebody that has one you can compare it to?

 

Buy a can of Seafoam motor treatment and suck it through your intake mainfold via a small vacuum line until the engine dies. Let it sit for an hour or so, and then start the engine. I did this on my 92 with 82k miles and the thing smoked like a bastard for 20 minutes. I drove down the street and I swear it was like throwing a smokescreen a la Spyhunter. My fuel economy improved afterwards. The stuff is great. They sell it at NAPA, among other places.

 

You could also try doing a engine vac to clear out the carbon build up. They run heavy duty solvent through the induction system and combustion chambers. Though a little spend (about $125 when I did mine) it really help the motor out a lot. It ran a lot smoother and fuel economy definately picked up. Though your compression does seem a little high, how did you perform your compression test? Did you relieve fuel pressue, pull all the plugs and get a reading, or did you pull one plug at a time?

S

 

I releived fuel pressure, then pulled all plugs, then hung throttle wide open...then performed the test

 

Alright, so most likely it's either carbon build up, or the compression gauge could be off, but not likely.