Compression Test Results

[CzchMex]

Ok so I dynoed my car for the first time the other day and it pulled ok for a stock engine minus LT headers that were a hack job from the previous owner.

However my issue lies in the burning oil. During acceleration after 5k RPM there would be small amount of smoke coming out of the exhaust. Then upon deacceleration it would smoke a lot.

So I decided to do a compression test. Here are my results: (1 is front 4 is back)

NOTE this was done on a cold engine

Passenger side:
1 - 131
2 - 122
3 - 121 - small amount of oil on plug
4 - 131

Driver side:
1 - 137 - very small amount of oil on plug
2 - 139
3 - 32
4 - 145

So obviously the 3rd back is super low on compression. However the car runs fine and no rough idle. It does have a super slight bump to the idle but that's normal I believe.

Anyhow I plan to do a leak down test to determine were the leak is.

How come with a psi of 32 I have a decent idle and power?

 

[SIC9250]

You triple check your gauge on that number 3 cylinder a few times while doing this? 32 is pretty much a dead hole my friend and your car wouldn't be running that efficent at all,hell none of those numbers are good,anything below consistent 130s is due for a rebuild,heads are about do for one atleast..get another gauge and try this again unless your confident in the equipment you used,I'd say yank that bullet and reload :rockon:

 

[CzchMex]

That's what I thought. I had to rig a couple of fittings together for this to work which might be where I am missing that extra PSI. However I did check the bad one a few times.

I may have to go try a different compression test tool. This one I had trouble threading it in at times.

 

[Midnight_Cobra]

Why wouldn't you do a warm test? Obviously a cold motor will show low numbers.

 

[na svt]

just put some oil in the cylinder and redo the compression check. If the psi is higher you'll know it's the rings. If it doesn't increase the problem is with the valves.

 

[CzchMex]

Why wouldn't you do a warm test? Obviously a cold motor will show low numbers.

I was having trouble even acquiring a pressure because of the kit I used took FOREVER for it to finally thread into the cylinder. So after trying many many different things the engine was cold. So I continued. Didn't even think about it.

I will try again with a warm engine and try a small amount of oil in the low cylinders

 

[SVTPete83]

Just for arguments sake, I had a stock motor making 480 to the wheels with a vortech. Went to track, saw lots of smoke on my last run, drove it home. Did a comp test and realized I had 2 cylinders at 0 compression. Drove car around like that once a week for a month. Car still felt really fast. Until I then blew 2 head gaskets. Even with low comp in a cylinder your car can still feel like it's running strong.

 

[65fastback2+2]

hell none of those numbers are good,anything below consistent 130s is due for a rebuild,heads are about do for one atleast..get another gauge and try this again unless your confident in the equipment you used,I'd say yank that bullet and reload :rockon:

incorrect.

the numbers are irrelevant...the delta of the numbers is what is important.

If they all read 32 in every cylinder, it is highly possible you have a superb motor and the gauge number system is different.

 

[SVTPete83]

incorrect.

the numbers are irrelevant...the delta of the numbers is what is important.

If they all ready 32 in every cylinder, it is highly possible you have a superb motor and the gauge number system is different.

This...Consistency in the numbers is what u are looking for.

 

[CzchMex]

Ok so ran the test again with a different adapter. Apparently the one I had was leaking too much. I also did the test after running the car.

Driver side:

1 - 180
2 - 181
3 - 179
4 - 179

Passanger side (engine cooled a little at this point)
1 - 170
2 - 165
3 - 162
4 - 168

Now I will redo the passenger side again later on when I have more time but I did do a quick leak down test of the passenger 1 & 3

The 3rd cylinder back had the lowest compression, however had about 5% leakage. Almost nothing. The 1st cylinder however had a 30% leak which I could hear through my oil filler. Yes I know it's the rings….sadly.

I will get the others done and see which ones leak the most, but my gauge malfunctioned and wouldn't reset back to "0" so I have to exchange it.

 

[Mentos]

Noob question, but what kind of numbers would be ideal across all cylinders? (even a car with just over 100K miles)

 

[iamtheshaner]

Noob - most all mod motors are in the 160-190 range static compression when warm. Cold compression results are irrelevant.

The published spec is that all cylinders should be within 10% of one another because cylinder balance is the most important thing as the engine wears. Compression drops as wear increases - it's just a fact. However, that doesn't mean a motor hitting 80psi on all cylinders is exactly "good". If normal "new" motor static pressures are close to 200psi with <20% leakage you can see that a motor with only 80psi is most certainly going to have greater than 20% leakage. It's not like the rod gets shorter or the combustion chamber gets bigger as it wears - sealing surfaces just tend not to seal as well as they once did.

ANY leakage WHATSOEVER through the intake or exhaust is bad. But, since no ring set seals 100% the industry standard (and Ford's) is no more than 20% through the bottom end.

It's always tough giving good advice when an "amateur" does a comp test because you don't know the accuracy of the gauge, whether or not there are hose leaks (like above), the engine temp when the test was performed or, most importantly, how fast the engine is cranking. Notice how the results above just get lower and lower down the line? The batter was probably getting low due to crank after crank after crank and naturally the faster you spin the motor the less time air has to escape. Hence the #'s will get lower and lower.

If he really does have 30% leakage through the crankcase on a cylinder that explains his oil consumption under high vacuum. 4v motors also tend to consume more oil than 2v motors because all valve seals leak somewhat and the more valve seals - the more oil burned.

Strangely enough Ford's oil consumption spec is 1qt per 1500 miles. This is a LOT of oil and rarely do engines actually use anywhere near this #. I actually have a hard time believing a motor that burns that much oil would pass a 5 gas test but who knows? All I know is if you go through 1qt of oil per 1501 miles Ford will tell you "That's normal. Take a walk"

So the OP has a choice here: 30% leakage through the rings is too much and partly to blame for your oil smoke. Is it worth your time and $ to rebuild the thing to reduce a little smoke and gain marginal output? Your oil consumption is likely within factory spec but the leakage sure isn't. Under warranty you'd be getting a short block. A remanufactured short block with probably 5 different bore grades assembled by some UAW turd with a felony who makes $15 an hour that is...