low compression?

[talon187]

ok for some reason ive got 120 compression across the board isnt that low? this is what my motor has
eagle rods
arp rod bolts
apr mains
arp head studs
.20
wesco pistions 9:1 compression
o ring block
stock head
mitsu 4 layer metal headgasket

i picked the motor up for a nice deal it had under 3k on it and i was told was in working order i beileve when i put it in i did a compression test and it had 130ish this was in june
i had the motor over heat once or twice but it never got to the H side it got between the h and the normal mark when it happened but the thing is on that my stock gauge is incorrect if the car runs for 3mins with 180 thermostat in it. the gauge says its up to temp but if you go under the hood u can touch the radator and all that stuff and its still cold any input would be helpful thanks

 

[DirtyBirdRacing]

You could do a leak down test to pin point your compression leak.

I think the service limit is 114 psi.

Bill

 

[RipperXX]

Funny I thought the service limit was 120, but with good tuning and enough boost you can still make plenty of power.


My guess is overheating caused the rings and cyl walls etc. to expand and ware off more of the piston ring, so now that the engine is not overheating there to small and not sealing well.

And if your temp guage is not working correctly try checking the stock temp sensors. If you still have problems I would start looking at a aftermarket coolant guage. As I have seen some stock guages show different readings. Such as my current Talon, it never reaches the stright up 90* angle for normal like my last one did, however after replaceing the coolant temp sensors it comes a lot closer than what it did before i replaced them.

Go ahead and do the leak down test but my guess is your going to have to replaces those rings. If you don't have a aftermarket radiator and have the cash a Koyo or Fludyne would also not be a bad idea. That and as well as possibly replace your thermostat if it is old.

 

[drewvr4]

yes 120 on 9:1 compression is terrible, you should be up near the 180 range with that setup, you definetely need to do a leak down test.

Search around the forums and read up on how to do it.

You can try putting a small capful of power steering fluid into the cylinder and then retesting the compression, if it goes up you know your rings are not sealing right, I don't really have time to explain the rest of the procedures

 

[talon187]

well i think i might of goofed on the compression test a tad i didnt have the throttle at woot and i didnt have it totally warm i didnt realzie i need the car hot so im going to do it again when i get my turbo back on and im going to put some oil in the cyclinders if its still low after doing that

 

[drewvr4]

well i think i might of goofed on the compression test a tad i didnt have the throttle at woot and i didnt have it totally warm i didnt realzie i need the car hot so im going to do it again when i get my turbo back on and im going to put some oil in the cyclinders if its still low after doing that

Wait what?

You need the motor warm but you don't run it when you do a compression test, pull the plug for the fuel injectors, right behind the rail its a triangular plug take it out.

Then pull your plug put it in there, turn it over maybe 5-7 times and then see what it is. Do that and come back and let us know

 

[talon187]

i know the motor shouldnt be running wasnt that hot is all. ill do another test whenever my turbo gets put back on the car hopefully by the end of the week i hope

 

[RipperXX]

Having the TB at WOT doesn't make a huge difference, if it were cold expect about 10-15psi more warm, so it is still not like new. But above service range.


So long as the cyl's give even pressure is the main thing.

 

[Spoolin4Ever]

I would redo the compression test as well, just in case it makes a difference, it is worth a try.

Although with my car I didn't notice much difference on my compression test whether it was warm or cold, and whether or not I held the peddle at WOT. It still came up about 150-155 regardless.