Re: Lightweight Flywheels to underdrive pulleys

[rusmaster <rusmaster@xxxxxxxxxxxxx>]

I'd like to chime in on the underdrive pulleys.

While underdrive pulleys can free up additional hp, they can have a negative
impact also.  The biggest being the water pump.  In the case of the
alternator, most BMWs use only a small percentage of the current capacity.  So
unerdriving the alt. is not as significant(uses less hp also, so the gain is
much smaller).  The water pumpis another story.  Spinning the w.p. slower
effectively resuces the the cooling headroom of the system.  This may not be a
problem until you take that summer trip to Las Vegas and you run the AC.  This
is where the reduced capacity of the system may break or damage the engine or
cooling system.

I won't address the AC pulley because these are harder to change since the
pulley on the AC units have the clutch system also.  Reducing the size of the
crank pulley will do, but is much more expensive and also frutile.  If you
wan't that hp, just odn't run the AC while at that track school.

Just somthing to keep in mind during this discussion.

Take Care,
Russ

snip

> After a lightweight flywheel, the next targets might be those accessories.
> One option is to put in pulleys that gear down the things they are pulling,
> thereby making their effective rotational drag on the engine much less.
> I know one person who claims such "underdrive pulleys" were the biggest
> performance gain he had done -- on the order of 17hp.  Comments?
> 
> Thanks again for the well-written and informative post,
> 
> Brian

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