johntorg

I just finished racing at the PCA races at Sebring. My 2.7L race car is consuming way too much oil. In 109 Laps I added 6 quarts of oil. The engine is not leaking and not really smoking badly. I did have someone saying there was a puff of blue smoke every time I shifted. I forgot to ask if it was on up or down shifts. The engine is not my usual race engine. I swapped in a street engine with a rebuilt head and new clutch when I blew my clutch late last season. It runs great and produces good power. Finished 8th, 4th and 3rd out of 16 cars with a best Lap time of 2:38 (by my co-driver), so it is making good power. When I ran it on the street, oil consumption was not an issue.

The compression was even and excellent. The bottom end has about 180K miles on it. I will do a leakdown test to check the rings, but I suspect valve guides.

Any input will be greatly appreciated.

Here is a link to a video of the car passing by the pits with no visible smoke even on the 5-4 down shift into turn 1 http://www.youtube.com/watch?v=8i-Rzi94eww

Juan Lopez

John, you must be on my video. I'll check to see.

Matt Romanowski

If it's using oil and not leaking, then it's an oil control issue. If it has cats, they can burn a decent amount of oil and smoke.

It's either the rings of valve seals. If it is burning that much, my bet is on the rings. It's not too hard to have a week ring set that allows a lot of burn.

johntorg

I guess I should have said it wasn't leaking when I started the event. At Sebring who knows what got shaken loose? I'll check it tomorrow when it is supposed to stop raining. Thanks for the video offer. My car is #119 in the Orange group and Black in the Enduro

Juan Lopez

I'll look for you. There was one 944 (not sure which) that had an unusual smelling exhaust.

IcemanG17

Have you modified the oil breathers? In my 16V 928 (basically 2 944 engines) if you have the stock breather in place it can inject quite a bit of oil into the intake at high rpm....in order to reduce that I plugged all the intake ports and vented the crankcase to atmosphere through a K&N filter....after sustained high RPM running (say above 5k) I do notice the K&N can get a bit moist....

For example in my last track weekend I burned 1 qt in 5 hours of running.....but quite a bit of that time was spent at lower rpm due to a race school I attended....typically I burn around 1 qt every 1.5-2 hours on track.....

johntorg

Yes it is still vented into the intake. Can anyone post a diagram or picture of a good setup using a vented catch can? I have heard that pressure can build in the crankcase if not vented properly.

Sterling Doc

If you are venting that much oil into the intake, you have a ton of blowby, and a ring issue anyway. These motors don't neccesarily burn oil just because RPM's are high. My last motor went a 9 hour enduro with only burning <1quart of oil. I'd agree rings, and then valve guides are the most likely culprits.

Oddjob

What oil level are you running? Full or over full? What brand/weight of oil? What pistons and rings are you using in the 2.7? I have heard that some aftermarket piston/ring combos do use more oil than the factory parts.

You can route the catch can in-line with the existing AOS/breather line, so it vents back into the intake, while oil is trapped in the catch can separator. Many agree that it is best to put the catch can and the crank case under intake vacuum. But others do vent the can to atmosphere.

Juan Lopez

John,

Can't see smoke from my videos. Sorry......... Juan

Bill L Seifert

My 944 puffed smoke when I lifted off the throttle and stepped on the pedal again, (downshifting). I had just gotten my cars head rebuilt, and the problem was the valve guides. The guy that did the head had not replaced the guides. They are bronze, and they do wear, and can leak a heck of a lot of oil. If the car has good compression and a fairly good leak-down. Then replace the valve guides. Bad news, obviously the head has to come back off.

I would bet it is valve guides.

Bill

333pg333

John as you have so many cars, is this a 2.7L turbo car?

johntorg

Thanks for all the input. I'll check the intake for excess oil tomorrow. I have a NASA race at CMP next weekend. I will install the catch can and see how much oil I collect. Its just a normal 2.7 NA street engine, that was my backup to the race engine in my car. As far as I know the rings are original. The head was recently rebuilt by the previous owner, I don't know if the guides were replaced. I'm using 20W50 Valvoline non-synthetic Racing oil. I fill to the full mark on the dipstick, although I did add about a half a quart extra for the 90 minute enduro. Juan, Thanks for checking your video. I really never saw any smoke when I was driving the car.

Droops83

I wouldn't condemn the valve guides just yet based on the info you have given. It is true that worn guides will increase oil consumption under all conditions, but the increased consumption usually occurs during deceleration, due to higher engine vacuum sucking in excess oil past the guides. While racing on track, you are of course decelerating while braking for turns, but you are spending much more time on the throttle.

I am not saying that it is not possible for it to be a valve guide/stem seal issue, just a little more unlikely than some are suggesting. My '86 951 is a case in point: it has 132K miles on the original head (and gasket, I'm on borrowed time!!!). It sees a good amount of track time, and I don't use much oil on the track (maybe a 1/2 qt every 3 hrs of track time). I know that my guides are wearing, because I use a good amount of oil on light load/high vacuum situations on the street, especially on they way home from Willow Springs or Buttonwillow, which is all downhill. Cylinder leakdown is still 4-5% across the board.

I would do a cylinder leakdown test and/or compare dry/wet compression to gauge the condition of the piston rings. I would also check the inside of the intake for oil. If there is oil present, I would suspect rings and/or a crankcase breather problem (though if you had the breather system routed incorrectly causing crankcase pressure, you would likely be having the dipstick popping out of the tube during track sessions).

Let us know what you find.

Oddjob

180k on the rings - it will be consuming oil. I would also worry about rod bearings, pushing a motor with that high of mileage. How does your high rpm, hot, full load oil pressure look?