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In Reply to: Re: bmw 745i vs porsche 968cs posted by John Stein on July 28, 2001 at 17:19:40:
Somebody finally pushed the right button.....
My stock 745 (6 psi boost and a 2.9x diff)was 0 - 60 in about 6.2. now at 15 + inches with a 3.91 ls diff ... well, I haven't clocked or dyno'd it yet...
To achieve a good start and a succuessful race..., select the 1 2 3 mode and holding the brakes firmly, give it 1/2 to 3 / 4 throttle. This will spin-up the turbo and eliminate most of the turbo lag... it also loads the engine against the torque converter.... The engine will be at about 2000 - 2200....if you slightly release the brakes, you can "smoke" the rears whilst keeping the front wheels from moving.... particularly if you are still running the TRX....
At brake release, accelerate to and shift at about 5000 rpm.... according to my dyno torque curves, both hp and torque start to decline above 5k....
If you have a un-modified 10/83 or later 745, you have a 10 psi cut-out. With a few very cheap mods, you can get a little more boost, but, if you touch the 10 psi limit (.8 bar) the fuel pump is shut-off until the manifold is back below ambient pressure .... a sure bet to loose a drag race.
One last caveat on the mods........
The stock 74 with stock perfect injectors and stock fuel pressures, will go dangerously lean above 8 psi. Now add in dirty injectors and off stock fuel pressures, or fuel delivery limited by a dirty fuel filter and you will be back against the knock sensors (if you have them and if they are still working.
Boosting the 745 performance can be done, but at every step, you start to reduce the "fail-safe" devices and design margins ... soooooooooo it is of course done at your risk and should be done slowly and carefully...
Nuf said.... 15 + inches of boost and 400+ hp is wonderful to behold in a car this size and this old....
There are many emparrassed pony cars, rice rockets, MB and Porsche in Atlanta...
Regards
John Stein
745 daily w / 222,000 miles and +15 in boost
85 ///M6 toy
Now, if you want to load the dice a little more, then there are some things you can do to raise the boost upto about 8 - 9 inches ( o
John i have learnt through the internet that you have done to your car the tuoma perfection mods.I wanted to make these mods to my car but strangely i cannot contct them and their website is not working.Are they really good?Does anybody know what's happening with them?
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