I disagree on the stewart pump, respectfully. The stock pumps definitely do the job just fine. However in my old 325Ci I upgraded to the stewart pump and found my average temperatures on my temp gauge read slightly lower. I don't have any numeric figures to genuinely compare or back it up. But I even noticed it lower when running in conjunction with a set of Turner Underdrive Pulleys.
In hindsight I wish I would have held on to those pulleys. I think I sold them for 80 bucks. But I didn't notice any real benefit from a honestly other than slightly stiffer steering on my 325 rack. That could have been in my head though. With pulleys, intake, and axle back I dyno'd 165whp lol
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