Delay Rebuild?
 

Maybe one of you guys can come up with an answer.

Car: 1979 930, 50k miles, 1986 exhaust, k-27, dual B+B muf.

Problem: black smoke

Symptoms: only at the track after a few laps, some black smoke from the left outlet only under full throttle. Back of the car has oil residue, by the end of the D.E. weekend white license plate turns grey. A few minor leaks on the ground after shutdown. Add about 3 qts for D.E. weekend No leaks when not driven in anger. Oil consumption well within limits street driving. I keep the oil level below 1/2. Sometimes I don't get full boost, .5 or .6. Full is .8

Question: Can I delay a rebuild? Can I drive this car at the track next year? What is wrong?

Thanks

Are you sure your turbocharger exhaust side shaft seal isn't shot? They can really smoke it up.

Black smoke is generally too much fuel.
I would suspect some sort of rich running condition caused by fuel injection system. This is generally a control pressure problem. Look to the W.U.R or if you're running an enrichment device I would check it out.
This would be a handy time to have an Air Fuel Ration gauge on the dash.
Good luck

Could be the turbo. Put it on the car when I got rid of the thermal nuclear reactors in 1998. How can I tell? Take it out and then...? If it is a seal, can I let it slide? How would this fit with the symptom with smoke out the left side outlet only?

Car gets 24mpg hwy, 16 combo, 7 at the track. Runs good. Starts good. No blue smoke at startup. Well almost never.

Not sure what the problem is then. Under DE conditions, you get positive pressure in the crankcase, which puts positive pressure in the oil tank (under high boost conditions). This pushes a small amount of oil back into the intake where it goes into the cylinders. Want proof? Check the intake circuit somewhere - heavy film of oil.

If you get 24mpg with a CIS car, oil usage within specs, I wouldn't touch that motor - I would frame it.

Nice car I'm thinking.

I've seen several similar (street 930, (951 too) to full race 911/935) do the same thing at the track. You sure about driving her on the track? How much oil did you run?

Yes, careful to go too far toward that slippery slope.

Let us know what you find.

Run some tests, looky here:

http://www.pelicanparts.com/techarticles/mult_Engine_Rebuild/mult_engine_rebuild-1.htm

-Wayne