Smoking at High Revs (sometimes)

Swiss911 · 09-01-2003, 09:43 AM

I had the top end rebuilt on my '87 911 about a year ago at 100,000 miles and have put 10,000 miles or so on it since. The engine runs strong with a noticeable increase in power. What concerns me is that it uses about a liter of oil every 600 miles (which I understand is at the low end of factory spec)

What bothers me even more is that every so often when I run it to redline it spews a lot of dark smoke. The next ten or 20 + trips to redline there is no noticeable smoke. Any ideas on what the problem might be? ... broken rings, etc.

thanks in advance for any thoughts on this

masraum · 09-01-2003, 10:12 AM

I have seen this as well. Only every once in a while, and it seems to depend on how I shift and mostly only happens in 3rd or 4th. It seems to happen on more aggressive shifts (quicker and possibly part throttle) Since it is dark smoke I believe it is primarily fuel resulting from more overlap of gas and clutch.

I don't think it's probably anything to worry about. If it was light gray or blueish smoke then it would be an indication of oil.

It's hard to say since at 95 and 125 it's hard to pay too much attention.

Tyson Schmidt · 09-01-2003, 11:58 AM

If it's black smoke, then you are giving her an "Italian tune-up". Which basically means you're burning off the carbon build-up. And actually, it's pretty normal under full-load acceleration to give off some soot in the exhaust on occasion.

If it's blue or white, like masraum said, it's burning oil. Could be from not-yet-seated rings. Maybe the engine wasn't properly broken-in after the top-end overhaul. What all was done in the overhaul?

Swiss911 · 09-01-2003, 12:37 PM

The overhaul included replacing the American pistons/cylinders with Euro spec higher compression ones, replacing the cam with a 964 cam, replacing valves and guides, changing to a high performance spring, and dropped the cat for a Euro premuffler.
The car runs great, idles steady, starts first time, ... but is pretty thirsty on the oil and occasionally leaves some pretty dark clouds behind.

I thought the problem might have been carbon build up because I use the car as a daily driver :15 each way to my office but the last time it created a cloud was after I had driven it to Northern Italy at high speed (4 hours) and then cut back through the Swiss mountains to test the cornering ability (5 hours) . I spent a lot of time close to or beyond 5K rpm so thought the engine would have been pretty clean ...

Tyson Schmidt · 09-01-2003, 01:23 PM

When you say "dark cloud", is it black to dark gray, or bluish white?

Swiss911 · 09-01-2003, 01:27 PM

Seems like black to dark grey to me ...

dd74 · 09-01-2003, 02:44 PM

The "Italian tune up" I've seen first hand on many cars that are driven "too easy." Swiss - how do you usually drive your car? Are you on it with regular agression. If not, the spewing might be carbon build-up as mentioned. Could running too rich have anything to do with the smoke?

Nathan M · Nathan M's Garage

I also have a Swiss 911 and I'm considering the mod's you've done. How much of a difference do you feel the higher comp & cam change have made? (was it worth it?) Have you had the car rolling roaded? Did you have an ECU chip change or are you still running with the original? Oh, and did you buy new pistons & cylinders? If so where from & how much should I expect to pay?

Swiss911 · 09-08-2003, 01:49 AM

Nathan, I think the mods made quite a difference in the lower and mid-range torque. On the rolling road, the car was making about 145 hp and the peak torque rating was about 20nm above stock. I had the ECU reprogrammed to take advantage of all the mods. The pistons and cylinders were bought from the same shop and came off of a car that had upgraded to non-stock components -- so the price was about 1/2 of what I would have paid if purchased new.