1990 GSX Compression Test Results with FP2's

[GSXlaunch]

Just wondering if this is normal; got exactly 150 on all four. Engine was cold and the battery was moved to the rear of the car. I also just installed Fp2 cams which have a little higher lift then 272's...I used to get closer to 160 before moving the battery and cam swap. I am assuming this is okay for it being cold, cams and battery being in the rear. Thoughts

 

[Black95TSIawd]

what does your battery in the trunk have anything to do with your compression. And yes being the engine was cold, that affects your compression.

 

[anconover]

Maybe he was worried the motor wasnt cranking over well enough. But 150 across on a cold engine is very good.

 

[BISHILVR]

performance cams will usually lower your compression some due to valve overlap and the extra lift and duration.

 

[TSIfreek]

I wouldnt worry about it as long as they are all the same you are good to go. I would check it again hot and should go up 10 psi or so. Testing the engine hot will aslo alow the engine to turn over faster since the oil is hot and thin. Also remove all the spark plugs and leave them out until you are done. This is real basic but you never now with the kids on this board with little expereance. Also the cams will lower the compression some that is true.

 

[GSXlaunch]

Maybe he was worried the motor wasnt cranking over well enough. But 150 across on a cold engine is very good.

Yup, just looking for some reassurance...and yeah all plugs were out :laugh: I also have the 4 layer mitsu metal head gasket which I think would lower compression a little. I could be wrong. Engine has 118k miles on it, head has updated lifters, arp's and 5 angle valve job. thanks

 

[TSIfreek]

Yes the MLS mitsu gasket is thicker than stock and will lower the compression some. 150 is good numbers for a stock motor with miles on it. Mine had 145 on it and it ran hard with 100k on the clock stock everything.

 

[diambo4life]

That's fine if you have a thicker HG. My car (last year) blew 150 across on a cold motor with stock gasket and stock compression with stock cams.

 

[turbotalon92]

Cams don't lower your compression.

 

[Mike1992]

My new cars got 89,xxx on it and the compression was only 136 across The guy i bought it from didnt go into details but said the t-belt broke just as he took off one time and it ended up being a $800 repair job. The did tell him that none of the valves were bent though, but my suspicions are the they might be slightly since my compression is so low. Any idea's? Sorry to rob this thread. The car runs excellent to.

 

[DSM90AWD]

The guy i bought it from didnt go into details but said the t-belt broke just as he took off one time and it ended up being a $800 repair job. The did tell him that none of the valves were bent though, but my suspicions are the they might be slightly since my compression is so low. Any idea's? Sorry to rob this thread. The car runs excellent to.

In my experience with DSMs a TBelt failure guarantees a trip to the new valve store. Though if one (or more) were bent, you'd get much less compression than 136. My comp was near zero when mine went.

Add a capful of oil to each cyl and recheck compression. My guess is that you rings have normal wear for a 13yo car as compression is still with in service limits (121-164psi).

 

[diambo4life]

In my experience with DSMs a TBelt failure guarantees a trip to the new valve store. Though if one (or more) were bent, you'd get much less compression than 136. My comp was near zero when mine went.

Add a capful of oil to each cyl and recheck compression. My guess is that you rings have normal wear for a 13yo car as compression is still with in service limits (121-164psi).

I agree. As long as it's uniform across the board, that 136psi is acceptable. Guys have run 10's with 120psi compression across.

Don't open the motor up.

What the hell did they fix then to warrant that $800 bill? That's what you would pay if they completely rebuilt the head (ie. new valves, valve stem seals etc) + HG replacement, timing belt, water pump install.) Talk about ripoffs...

 

[Mike1992]

Im not sure of what was replaced. The guy I bought it from, doesnt know jack about cars. My guess is they pulled the head to find the valves fine and put it all back togeather with a new timing set. But jeeze 89,000 miles and a perfect 136 across kinda sucks.

Thanks again for the hookup Diambo, I owe you

 

[GSXlaunch]

Guys have run 10's with 120psi compression across.

whatty-whattan? If that is true that is kinda cool...

 

[GOTLAUNCH?]

My #4 and #1 cylinders had 160-165 and my #2 and #3 had 150-155 on a 108k motor 94 GSX. I'm pretty sure on a cold start that it's near stock. Stock I believe is somewhere near 163 for stock? Correct me if I'm wrong not positive

 

[diambo4life]

whatty-whattan? If that is true that is kinda cool...

You just need alot of boost and good tuning.

Mike, if it's uniform across, I wouldn't touch it. 121-164 is the factory compression range and I bet you maybe you have slightly bent valves. There's no way you snap a t-belt on an interference motor like the 4G63 and not bend any valves. When I bought my car, it read 120 across (hot.) I swapped the head and it blew 150 across (cold.) I did run a 13.0 @ 104mph with the 14B at 17-18psi with the low 120 compression too. That's why I am insisting on not messing with it just yet. If they installed a shitty/cheap FELPRO HG (it wouldn't surprise me) and it blows on you, mess with it then.

 

[Mike1992]

Once again, sorry for stealing this thread.

Diambo I dont plan on pulling the head anytime soon. I dont have the know how to put things back togeather. But if you do have some spare time i would like, if you could, come over and look it over. I got all the fluids drained (NASTY) and i got a few minor oil leaks by the oil filter housing, that Im not sure where its coming from exactly. That and your DSM god around town so you know best, . Right now im waiting on parts to get this thing running. Gimme a call 353-0443 TTYL

 

[waiting2bl33d]

hurray for springfield, MO DSMers

 

[STHPERFORMANCE]

I bought my 1990 Talon AWD about 3 weeks ago. Bought from original owner and never was modded.. On a weak battery is did 150 150 150 157 across the board...

I was suprized for it having such great compression and having 168k original miles..
Runs like a wet dream and shifts perfect..

 

[GOTLAUNCH?]

Actually I did a compression test today and my results were (from #4 cylinder down) 170, 170, 155,150.

 

[DSM90AWD]

My 1990 with 130K miles has 170-172psi accross all 4.
A bit high but prol due to carbon buildup or maybe Satan shaved my head when they rebuilt it years ago (T-belt tensioner recall saved me much $$$ ).

 

[Mike1992]

Jesus out of all of you I have the lowest miles at 89k and the lowest compression.(136-136-136-136) That kinda sucks ass.

 

[sweet97]

Just checked mine and all were near 115! No wonder I feel the car is slow when you condider my mods. Mark

 

[Mike1992]

Just checked mine and all were near 115! No wonder I feel the car is slow when you condider my mods. Mark

That sucks, time for a rebuild Whats your mileage?

 

[12sec92Tsi]

I know last summer when my belt jumped a couple teeth, I thought I bent some valves but didn't bother to get a compression gauge and do the test because it ran fine. Just this past March I got one and it read 155 across on a hot motor. I lucked out.