[nonovurbizniz]

imo they're silly...

There are two types... crank pulleys that underdrive everything... and accesorry pullies that underdrive that component...

here's why I think each are silly.

Acc. Pullyes.
They underdrive each individual component...

Power Steering... the only real time it does ANYTHING is when you are idleing.. or at VERY low rpms... other than that the pulley is hardly ever draining power... SO when you underdrive it it takes higher rpms to achieve the same power... basically taking away the effectiveness of the powersteering... I wouldn't be suprised if a looped system with a breather (IE.. entirely remove the power steering pump pully belt and lines) would turn easier...
However I've never had them so... I could be wrong...

Alternator... If you have any dimming of the lights at a stop at night it's gunna get worse... if you have a big stereo or other elec. aftermarket stuff it's not going to run them as effectively...

Also underdriving electic motors (basically what an alternator is) can be VERY bad for them and quickly deteriorate the lifespan of it.

A/C... well again underdriving a compressor is going to effect both it's life and effectivenes...

Crank Pulleys...

Most are not properly balanced (causes bearing fatigue/failure at high rpms). they also have no dampening which is ok on some models (internally balanced/dampened blocks)... but definately not ideal...

And again these underdrive all the accessories... which isn't ideal...

Automotive engineers usually design everything to be operating in a specific range...

For example... you can add pressure to the fuel rail/system and make the injectors flow moderately more but it wears them out faster than normal (not to say they won't last a long time still) and they do have a limit (not too far above the stock flow)... if you drop pressure to them they will flow less but again there is a limit... without enough pressure they will NOT perform properly at all without enough pressure...

With all this said... I'm sure the aem ones aren't going to kill your car or accessories but they are VERY expensive for very little gain...

Like said in the other thread... they are really a final touch... when you're trying to free up ANY final few hp...

They increase power by freeing up otherwise drained power... the more power the engine has the more power will be freed by lightening the spinning load...

For another example "race only" cars will generally resort to running electic water pumps to be running as few accesories off the crank... While it will benifit a street drivin car it's not by anymeans the best way to spend your money. (unless you have already bought all the better things).