Over the last couple of months swapping back the old cylinder head from the blown 3.0L motor has been of primary concern (see european car 06/02). After evosport pulled the 3.0's cylinder head, we discovered it was simply a broken copper head gasket--the cylinder head and block are fine. Noticing how clean the pistons were even after 6,000 turbocharged miles, I decided to have the cylinder head swapped to the old one, because with the current one on the 3.2L the car has been going through oil at a rate of one quart every 400 miles on the street (and much worse on the track)--this is not good.
Looking through the spark plug holes on the current motor, it was evident oil was present on the top of each piston. I had the cylinder head rebuilt once before, and while the head was off I could see the centralized oil deposits on the pistons, indicating most likely a leak from the top end. Not surprisingly, the car was still consuming oil at the same rate after the rebuilt head was installed--it was time to put the old one back in. Fortunately, the Bavarian Engine-built block is still great, helped by the Techron I've been pouring through the intake from time to time to clean out the combustion chambers and piston tops--as discussed in Part 19--to help avoid detonation.
The car will visit evosport once again for the swap. Once the original cylinder head is reinstalled, I foresee a lower octane requirement for high-boost runs, since there won't be oil deposits present to heat up and predetonate the fuel.
Since the turbo will have to come off during the cylinder-head swap, one of two possibilities will happen: Either the fins of the current Mitsubishi turbine will be clipped a few degrees for better flow (the Garrett compressor side untouched) or the entire unit will be replaced with another. This actual unit is fine, but the EGTs are a little high for my taste, especially on the track. The exhaust sees as much as 1,250*F on the street and as high as 1,390*F after several laps on the track, but these temperatures are measured right after the turbo--the temperature coming out of the actual exhaust manifold is probably getting up to over 1,500*F. Much of this has to do with the log design of the Active Autowerke exhaust manifold. Unfortunately, there isn't room for an equal-length, tubular design at the moment either.
If I go the new turbo route, it won't be necessarily to make more power--more than 400 at the wheels is plenty for me. Instead, I'd like to see over 400 whp with less boost, see a quicker turbo response, and hopefully see slightly lower exhaust gas temperatures. If this is accomplished, it will be well worth it. Since the exhaust manifold will be off as well, I may even get it thermal coated to further lower the underhood temperature.
A new product has made it onto the car, however. Because of the on-track fuel starvation problems I was having under hard cornering, Bimmerworld came to the rescue with an anti-fuel-starvation kit. Until now, I've had to top off the fuel tank after every 20-minute track session because the car would hesitate under hard right turns, with nearly three-quarters of a tank of gas still in there.
Unlike its Stage 1 system, Bimmerworld's Stage 2 system uses two pumps instead of one, and they're interconnected on each side of the fuel tank, ensuring nearly every last drop of fuel is sucked out of the driver and passenger sides of the fuel tank before the car actually runs out of gas. The beefed-up AA unit still acts as the primary pump, but under hard right cornering, when the passenger side of the tank goes empty, the second pump delivers fuel to the motor to avoid hesitations and a "leaning" of the air/fuel curve. The unit is a relatively easy installation--give yourself about an hour to an hour and a half. evosport installed the system with no problems.
Bimmerworld, along with a variety of other BMW Club racers, uses this system on its race cars with great success. I haven't had a chance to fully test the system on track, but I will report back with my findings, and see if I can finish a couple of sessions without fuel starvation, caused by my 5- to 7-mpg average on track.