This seems to be a very popular on some of the other forums, especially the E46 guys. My personal feeling is this is not advisable. The cooling systems on the M5x motors are not sucking HP that is going to make much difference. What worries me is that the cylinder heads on the M5x are very susceptible to heat, they are extremely thin, so thin that you can not surface them and reuse if you overheat.

Thats a minimum of 2k if you toast a head gasket and closer to 4k if your head gets warped, most people throw in a junk yard engine and sell the car. There is simply no safe HP left on the table with the 6 cylinder M5x engines. If you feel under powered you should sell and buy a 4.4 or larger. BMW engines and the 6 in particular will take you well into the 100k range and 200k is not a problem with care. Look at it this way, BMW only found about 25HP in about 12 years of production, and much of that came from increasing the displacement. That should tell you how close to the limit it was designed and put into service with. I think the 6 cylinder BMW engine from 92-05 is possibly the most reliable and well built engine of it’s size ever produced, and there are some amazing engines in that field, none of which will draw more argument to my statement than the 3.0 Porsche flat 6. The rest of the contestants are to far behind to really make an honest run at the “best of class” 6 cylinder.

Don’t mean to hijack your thread, but I say the fan delete is not worth the 2 or 3 dyno HP to risk.