Compression Test Results

[thomas91169]

Just did a compression test while replacing plugs (TR6 @ 32 btw)

Pass................Firewall..............Driver

180___________________________175
175___________________________165
180___________________________150
175___________________________165

........................Front.....................


Any input?

AllData says that the lowest cylinder must be within 25% of the highest cylinder to be within spec(or if 180psi, lowest can be 135psi) so according to that i am within spec. Just kinda surprising to see the right bank so off.

 

[T-Pain808]

I was gonna ask why you needed a compression test, but I just notice its
up for sell.

 

[IronTerp]

The right bank may have a slightly different deck height which could cause the discrepency, but you do have 175 on both banks. That #6 is a bit low for sure.

 

[Jomo1994z71]

Agreed...150 is pretty low...I did a lot of research on these tests before I bought mine...

 

[JedWele]

A lot of times these mod engines are a little off on the Cam timing between the two banks which may exaggerated the #6 being low

 

[MaximumVelocity]

The right bank may have a slightly different deck height which could cause the discrepency, but you do have 175 on both banks. That #6 is a bit low for sure.

Or the cams can be off by a few degrees (within factory tolerances) in one head.

 

[thomas91169]

I was gonna ask why you needed a compression test, but I just notice its
up for sell.

werd, more or less it was just for shits and giggles, i mean you have the plugs out, why not check compression anyways (pending you have a tester within arms reach)?

the motor has 66k on it, and has been pullied since the 5k mark (according to the original owner, im owner #2 and #4 lol). I actually expected both banks to be low, when i first did the pass side i was like "holy shit!" then got to the drivers side and it seemed more realistic. i dunno if i was doing something wrong (or right?) on the pass side, then again i dont see how you can **** up a Compression Test.

I think cam duration/timing is the best answer to the overall discrepancy between the two banks. I know damn sure its not from the tune, its a canned tune for a 2.76" (which are pretty safe as it is) but the car now has a 2.8" so if anything its extra safe.

 

[mike302]

those numbers are good, I wouldn't even worry now about them, I just throw it on a dyno and get a base line dyno and check if everything is ok and if you still have the same power or about the same #s

 

[TrickStang37]

it could also be that the engine was beginning to cool down some.

 

[SnakeBit]

it could also be that the engine was beginning to cool down some.

Bingo! :beer:
Try it again but start with the driver's side first. See if the numbers agree.

 

[IronTerp]

Or the cams can be off by a few degrees (within factory tolerances) in one head.

Good point. I did a compression check 3 years ago and had a goofy cylinder like that. Cobra seems to be running fine though. ;-)

 

[thomas91169]

it could also be that the engine was beginning to cool down some.

good call, didnt think of that.

will have to try it again starting with the drivers side.

 

[thomas91169]

****.

well after this thread i tried with a warm motor and the compression results on the drivers side went up to around 175 across.

then a month or so ago i overheated probably 3 times (didnt know to fill at the upper cap after removing overflow tank to reinstall stocker, got sick of polsihing it every week!) and went through all that, and then two weeks ago the car went to the body shop for some little repairs (got in an accident and killed the frnt bumper but everything else was good) where they said they removed the radiator to recomb the fins, well of course they didnt refill it correctly, so i overheated again on the way home, knew exactly what it was, got into the garage and refilled the correct way and all is fine now.

except for drivers side. New numbers:

Pass................Firewall..............Driver

180___________________________175
180___________________________165
180___________________________155
180___________________________130

........................Front.....................

so yeah. needless to say, stomach is in knots right now. dunno if i should be a douche and blame it on the body shop for improperly refilling it and letting me overheat, or be a man and realize it was probably my fault for 3 out of 4 of the occurances. The above i started with a very warm motor, got home and let it sit for about 30min and started with the drivers side.

looks like its new HG time. gonna do a leak down tomorrow and pinpoint the cause. Anyone know how much a set of gaskets and some ARP's cost for our cars?

 

[Duran]

Sorry to hear what happened. But you should have fixed the overheating problem the first time it happened. But its to late now for pointing fingers. Its time to rebuild and make her bigger, better, faster!

 

[thomas91169]

yeah i didnt have my compression tester though, buddy of mine was using it.

if anything ill just pick up the oem kit from lethal, do some odds and ends (paint valve covers and blower, cooling mod, etc) and throw in a good clutch while its out, mine should be dead 40k ago but so far every owner has sworn they didnt touch the clutch and it just hit 70k. I dont need some crazy rebuild, i have no plans of throwing down 700+whp anytime soon. more or less was looking to sell and get out of payments for the time being and get into a house since its so freaking cheap, and then when things turn around refi and buy another in cold hard cash.

 

[svtnos1011]

makes me want to test my compression for the f-k of it but I am afraid in case something is bad:whine:

 

[MaximumVelocity]

Scope the motor and do a leakdown, you very well may need pistons and an overbore. These cars usually don't pop head gaskets, even when overheated.

 

[Jomo1994z71]

This is the reason I always am with the person that touches my car...sorry to hear...

 

[thomas91169]

UPDATE:

was at a buddies house earlier, big car guy, has a lift (ding midpipe swap is cake with one of these!), every tool imaginable, super knowledgeable. Was talking about the whole compression situation, decided to do a leakdown test so i can have a second set of eyes seeing what i saw when i did it.

pressurized the tester to 0% on the leakdown gauge, set it and no leaks. nothing. not even from the exhaust. he was like "umm, you said this has low compression, not from the looks of it!" so i was like "yeah, 130 on that cylinder" and stuck the compression gauge on the end, pulled the coils and proceeded to do a compression test just to show him.

160psi (on the cylinder that i pulled 130psi from), not to mention it was on a cool motor.


so wtf. either i somehow wasnt doing that cylinder right (maybe not screwing the tool in enough?) or i have a self-healing motor.

 

[Un4GivN]

Awesome news!