# underdrive pulley



## DRFTGTO (Dec 25, 2008)

Does replacing your stock pulleys with underdrive ones make a noticeable difference?


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## B-ville Goat (Oct 5, 2008)

By itself, not really. Most say 5 horsepower or less, not worth it to me. I also don't like slowing down things like the alternator on anything. Spinning slower lessens it's efficiency and ability to keep up with the demands of everything.


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## LOWET (Oct 21, 2007)

DRFTGTO said:


> Does replacing your stock pulleys with underdrive ones make a noticeable difference?


A noticeable difference. Not really. At least not enough that you will feel it . When I had mine installed I gained 4 HP and 6 RWTQ .ON the Dyno


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## GTOsarge (Oct 9, 2007)

I did mine as part of a combination of upgrades all at once.


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## gurkgurkgurk (Oct 2, 2008)

dont risk ruining your engine for alittle horsepower. when you use underdrive pullies, it slows down everything, including your alternator and water pump, sure it may be fine if your using an electric water pump, but think about how your affecting your battery, not to mention if your running aftermarket speakers and subwoofers. and if you are running the stock water pump just think about how hot the cylinder heads are getting. if you want extra horsepower look elsewhere.


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## Rukee (Feb 8, 2007)

I've only had bad experiences with underdrive pulleys.


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## Tri-Power (Jan 10, 2008)

*be careful.*
This is a write-up done by Steve Dinan (very respected in the BMW world.)
It makes great points, and is a good read for anybody pondering underdrive pullies.
I read it on my home forum so that's were I'll link to:

Underdrive Pulley Tech - Purdue Automotive Performance Association


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## NEXSTAR7 (Jan 28, 2007)

very good reading. i was about to spluge on some underdrive pullies. thaaaaank you.


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## BWinc (Sep 21, 2005)

Scratch one from the mod list.


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## dustyminpin (Jun 19, 2006)

My tuner at the speed shop said they were good for about 6 hp. He asked me why I didn't go that route when I had him install my Summit Racing SFI harmonic balancer (OEM replacement, not undersized). I told him it wasn't worth it to me due to all of the issues mentioned above. The reason I switched it at all during my rebuild was because I was wearing through AC belts about once a year to year and a half and getting signs of wear on the serpentine belt and did some searches on the net and found that an achiles heel on the LS1s (on vettes anyway) was a garbage factory harmonic balancer causing belts to squeek and wear, same deal I was experiencing with my LS2. So for 200 bucks, I upgraded to an SFI approved balancer, looks much nicer too, with its shiny chrome like finish.


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