Underdrive pulley for a V6

LTorve said:

How exactly do underdrive pulley's function? how much power would I pick up if I installed one on my 4.0 v6?

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I hadn't heard of an underdrive pulley before, had to look it up -

http://1.cdn.lib.americanmuscle.com/files/bbk-underdrive-pulleys-install.pdf

Apparently it replaces the crankshaft pulley and the water pump pulley. I'm taking a wild guess here, but it looks like the new crank pulley is a tad smaller in diameter and the water pump pulley is a tad larger in diameter. I would think power pick up would be minimal, but AM claims 12hp. Am sure those more knowing will chime in.

If my crank pulley was defective (as it seems they go out often in our cars), I would consider the kit as the pulley looks to be a quality unit. Otherwise, I wouldn't bother due to the cost and hassle. But that's just me..

amustangrocks said:

ive got one on my car i got from longalan when he supercharged. it is smaller in dia. and you need a different size belt. i just replaced the belt, got it from cjpony.

i have not noticed any adverse effects on cooling, steering, charging ect. it turns all the accessories slower. i couldnt tell any huge increases in power but id already had a bunch done. i do think all the little bolt on mods add up at some point. my car runs real well for a n/a V6 (14.7-1/4 mile), very spunky.

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Am curious, did you replace both pulleys? Looking at the documentation, looks like you can use the same belt as the diameter change in the crank pulley is offset by the change in the water pump pulley?

Yes, spunky indeed..