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Underdrive pulley for a V6

1696 Views 6 Replies 5 Participants Last post by  s197inthe208
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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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. :)
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..
i only changed the crank pulley. they didnt offer any other pulleys back when i did it, but the whole idea is to slow everything down and pick up some robbed power. i know the gt has a set of pulleys. things might have changed in the last couple years. i didnt see the 4.0 listed on the bbk stuff. ASP was the only one making a underdrive for the 4.0 that i know of.
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