why is my compression so low?

[srdub-t]

I have a red top sr20det and when i first got it i tested the compression and it was perfect. Then i put a cometic head gasket on and some cams and it seems like it runs fine. Pulls pretty good i ran 13.1 at 110 mph with a t28, bc cams, gasket matched pp head, full exhaust on 9 lbs yada yada yada. so i assumed that every thing was fine but i decided to compression test it for the hell of it and the numbers were 135 150 140 140. What the hell??? im in the middle of a new turbo setup so i dont have my intercooler pipes hooked up but im pretty sure that has nothing to do with it. What do you guys think?

[sx_hatch]

i know what your problem is, its an sr20 you need an ls7

[CoupedUp]

i know what your problem is, its an sr20 you need an ls7

You're a d!ck. Was the motor warm? Throttle Body open?

[srdub-t]

hahaha yea an ls7 would be VERY NICE. but no my throttle body was closed and engine was cold but does that even matter?

[sx_hatch]

You're a d!ck. Was the motor warm? Throttle Body open?

i was just playing wit him inside joke

[SpeedRacer1]

Those numbers are within specs for an SR...

[TheKryptKeeper]

The throttle body does make a big difference on most motors. If the plate is closed, then the only air that is getting in to be compressed is what will fit through the idle hole. I have seen cases where it makes a huge difference and I have seen cases where it does nothing. More the former, however.

I would think that that is why you have low numbers.

The engine being warm just makes the rings and all seat a bit better, more importantly, you should swuirt a little oil in the cylinders.

I think that your copression sounds fine, however. Mine is currently 50-42-35-25. Be happy.

Krypt

[nwmrkt]

when you have low compression...what causes that? A full new rebuild would of course remedy that correct?

[Logan76]

Yes, but theres always the possibility that you could replace your old worn out head gasket and have perfect compression afterwards. If your not having machine work done to your head or block I would recomend stock HG and ARP head bolts.

[srdub-t]

yea i replaced my head gasket with a cometic but didnt resurface the head or anything. just to lazy i guess. And iv heard about the cometics not sealing unless the head and block are completly straight but i used copper spray and just put it on.

[biglipzit]

What thickness head gasket did you put on? A 1.1mm gasket will lower your compression but let us not forget that you have ran it a bit and if your running on the rich side you will have carbon buildup in your cylinder and on your valves. Could always be a small bit of carbon debris stuck in your valve seal not allowing them to seal perfectly.Have you ever heard of seafoam? Napa sells it. Buy a can and follow the instructions for putting it through your intake and try it again. It should dissolve all carbon and maybe remedy the problem if it isn't the headgasket.

[srdub-t]

yea the head gasket is only like .02 bigger than stock. But ill seafoam it and do a comp test again when the motor is warm and the throttle body open and see what happens thanks for the help everyone.