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Re: is there a way to defeat turbo lag for 5-spd 7 (archive)
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Posted by Brian on May 21, 2001 at 12:36:15:

In Reply to: is there a way to defeat turbo lag for 5-spd 745i posted by ...tom on May 18, 2001 at 14:51:26:

Lot's of ways. Cut off the Cat and Resonator and run straight pipes off the Turbo Down pipe. Turbo will spool twice as fast! Second, get higher ratio rear end. I have a 3.46:1 and the car revs up quicker. The turbo in this car is HUGE. A smaller turbo would help but they don't make any kits for this car that I know of. Also if you find a turbo with more impeller (not compressor) blades you will get a quicher spool. Get larger intercooler pipes (more volume at same pressure!) These are all simple tricks to get more from a turbo without even touching the boost pressures. Then there is alway the fast route most people take and that is adding pressure to the engine. I think this should be done last after all the above mentioned suggenstions, b/c your motor is only as strong as the weakest component. If you over stress one component more than the others can handle you break things, very expensive things.

If you want instantaneous boost you want a supercharged engine. Turbo's by nature have lag. But you get better overall Fuel milage and you still get neck snapping excelleration. Once your into boost if you are under hard excelleration you should never end up with the car "out" of boost after making a shift or you need to practice power shifting a bit more. Keep any turbo car up in the revs and you should have near instantaneous boost when you step on it. The lag comes into play while the turbo is waiting for the exhaust gas velocity to increase the speed of the impeller which creates boost on the compressor side of the turbo. That is why most gas turbo engines have lag to about 25-3000 RPM and beyond that it is almost non existant.

is there a correction that can be made so the 745i becomes more suitable for a 5-speed swap? any change in turbo or electronics? anyone like their stock car with a 5-speed? i've got the itch....

...tom




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