I can hardly believe the difference in my '88 740 Turbo! I notice better throttle response across the power band and fuel mileage has gone up by 3 mpg!
What did I do? I flushed out the cooling system and replaced the nasty brown crap in there with a fresh 50/50 blend of dex-cool and distilled water. I suppose that since the core temp is lower, and the turbo temp is lower, the engine is getting a more highly compressed air charge and so more power. At any rate, the difference is remarkable and the most power per dollar I've found.

sd

After change all my turbo/intercooler hoses I noticed quite a big difference in throttle responce, acceleration and turbo lag. Of course I had a air leak somewhere but I don't quite remember the car ever running so good. Moral of the story is making sure all your turbo/intercooler hoses are in good shape will also equal better performance. Hoses aren't as cheap though :)
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1988 760Tic - 156,300 1966 M-B 230 sedan - 98,000 1982 Rx-7 - 201,000 Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us. - Bill Watterson

ovlov,that reminds me of something else I did. There is a thin vacuum line running from the throttle body over to the turbo, and the turbo end was looking a little ratty. So I undid the clamp, clipped the ratty end off the hose, and reinstalled. I can't "prove it", but I know that any vacuum leak is a power thief. Details,details...I love them! :-)

While your at it don't forget to clean the Turbo hose system of oil including the intercooler and varnish off the throttle body.