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Re: 745i Rookie wants more boost!!!!!! (archive)
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Posted by Afshin on July 10, 2001 at 23:31:54:

In Reply to: Re: 745i Rookie wants more boost!!!!!! posted by Matt G on July 10, 2001 at 15:16:41:

Thank you very much Matt! As usual, your experience save people (me) alot of precious time...Could you just please tell me how much in BAR does make the 14 PSI's of pressure? Or just tell me the original 745 pressure in PSI's and I would do, compare.
Regards, Afshin.

You can get alot more torque! You need to figure out what your limits are going to be before you worry about how much power your going to make. From my experience with other cars with little motors and big turbos like the 745, the point between tearing the motor out of the car every week to rebuild due to over stress, detonation, etc seems to be about 400HP. This does not mean you will have 400 horespower the the wheels, more like 350 and a bit over 400 FT LBS of torque (american rating) Anything over this you will probably be destined to a life as a slave to your car. The power ratings I am quoting are mine and that is even on the ragged edge of destruction as these cars were never ment to do that and I only run 14PSI (not bar, not HG.. PSI). Anything over this is sure to eliminate the transmission pretty quick along with many other things. If you think you want to go to a 5 speed, knock about 1.0 - 1.5 seconds off your 1/4 mile time as the 5 speed on a turbo is never going to run like the auto and even the OD 5 speed is not near as strong as the ZF22HP. These are not race cars, but you can make 300HP out of your car and never have any problems and thats very respectable and the skys the limit depending on how much you are willing to do. Its no late model M5, and mine is not even that with the stuff I have done, but its darn close and will out MPH an M5. I suggest not going crazy and keeping the boost somewhere around or less than 14PSI.

Thanks Matt, I guess I'll modify the whole waste gate and go for higher octane. To get more compression ratio (8:1), I'm gonna give the engine head for some work and put the whole thing with a copper gasket back on. Mine's already got 7.5:1 (the secound serie of the early ones) so it shouldn't be a such a hard job to do. How much more torque do you think I could expect from this modif.?
Regards, Afshin.
PS, next, I'll also take care of the exhaust line.

Simply unhook the hose and the computer is no longer in control of the boost. It is now controlled by a spring that opens up usually somewhere around 10PSI. This is not a whole lot more than you have now, but is still more and will give your 3.2 at least 25HP. You would benefit more from a modified waste gate as you could add even more pressure on your spring. Just unhooking the hose on your car will go from 8 to 10+ PSI. 98 octane is ok as long as you dont go stand on it from coast to coast. Any more that 10-11PSI will require more octane in the level of 100.

Early cars have 8PSI turbo boost and lower compression, 3.5s have higher compression and 6PSI boost. The later years have to have the chip as the motronic shuts off fuel at 10PSI or more (this was to keep you from unhooking the hose and blowing it up) but gain quite a bit more from mods, the early years do not need a chip and just require a waste gate for high power or the hose unhooked for fair power that will be very safe.


Hi Matt,
What do you exactly mean by pulling the hose off the waste gate? I'm very interested because mine is a early one and would love to get some more power out of it. What do you mean by alternative fuel? How many octane? would a 95 octane be OK, or I have to go on for a 98 one?
Many thanks, Afshin.

If you have an early 745.. just pull the hose off the waste gate. This will give you about 270-290HP and its about max without going to alternative fuels. If you have a later 745 with the motronic boost safety shut off, you will need a chip that will tell the motronic not to shut the car off at 10 PSI or greater. I may be able to help you with this depending on which series motronic you have. Then unplug the hose then you have about 300HP and that to is about max without doing other things. All these mods are risky if your car is not in top mechanical shape but are reliable when the car is right and not abused and not raced 100% in hot weather. If it is your only car, I suggest not doing any as you may be stranded with a blown head gasket, detonated ring land, burnt piston and even worse, but if you have a back up car, have at it as you will like it but just be carefull.


Okay,

My car has about 130k miles and seems to run well enough. But, I desire to turn up the wick a little by increasing the boost. I know several of you have performed this mod. What are the risks? How much boost can I run with pump gas? And what are the projected Hp gains vs. boost? I have access to a machine shop and am not afraid to get my hands dirty. Any help would be much appreciated.

There is a finland based company named "Tuoma perfection" that can give you some answers.They make a kit for the 745i which includes tweaked motronic and more boost.The result of this stuff is 400bhp and masses of torque.See them on their website www.tuoma.com





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