I would like to go to a smaller S/C pulley but I'm worried about over spining the water pump. Has this happen to a lot of people. When did Mini come up with the better water pump seals. My car is a late 04 with many 05 parts, am I ok?
M

 

My 2 cents: the pump should last long enough until the M62 kits arrive and make it a moot point.

Wasn't this answered in your previous water pump threads? The water pump will not spin any faster than now if you simply lower the redline ~150rpm per -2% pulley reduction. Specifically, the water pump is turning at exactly the same speed at 7,137rpm with a 17% or at 7,018rpm with a 19%. And coincidentally, the efficiency of the supercharger itself falls off so greatly at such high rpm with small pullies (continues to increase boost, but heat even faster) that you'd be better off shifting sooner anyhow.

It depends what you want the car to do: this limitation in rpm capability is more than made up for by the greater low end torque... for a street car or drag racing where high rpms are infrequent. For sustained high rpm operation in road racing a larger pulley would be recommended to keep charge temperatures down and the belt alive.

Of course, the M62 solution promises to let you have your cake and eat it too...

 

I agree with BFG9000 100%, but if it helps I now am over 95,000 miles on my Sept 02 build MCS. 60,000 of those were with a reduction pulley, and 50,000 of those were with a 19%. Water pump is fine. No cooling system leaks. No overheating. No high oil temps. Never shredded or lost a belt. Ever. They've all been replaced between 15,000 and 20,000 miles just to be on the safe side, but each removed belt had life left in it.

For the record, I do not do track days or road racing (just lots of autocrossing and street miles). That's a very different duty cycle and would merit a different approach if you aren't dealing with a dedicated car.

Scott
90SM

 

Let me ask a question: If the hypothetical ratio of the water pump pulley, with regard to the crank pulley, is say 4:1 (just using these numbers as an example), then why would changing the s/c pulley change this ratio or make the water pump turn faster at all? The actual speed of the belt is determined by the crank speed and pulley dia, not the s/c pulley dia. Put whatever pulley you want on the s/c and it won't change the speed of the water pump pulley. Now, changing the crank pulley is a different story. Am I missing something here by saying this?
Rich B.

 

The supercharger shaft has the drive pulley on one end and the water pump on the other. Anything you do to change speed of the supercharger then affects the speed of the water pump.

 

The water pump on a MCS (w/M45 SC) is driven by the SC shaft. Change the SC pulley speed and you change the water pump speed.

edit: Doh!... what he said

 

Thanks for clearing that up for me guys. Hanging around too many V-8's I guess. Info appreciated!
Rich B.