# underdrive pullies worth it?



## youngGoat (Aug 14, 2010)

I have a 2006 M6(bone stock) and looking at some relatively cheap mods, and saw the SLP harmonic balancer under drive pully. wondering if there really is a noticeable power increase and is it worth it? also it seems pretty straight forward to install, would i need a tune?


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## Mike_V (Mar 10, 2006)

No way you'll feel it. I only have it because it came with all the other SLP stuff. It is free power though, however little it is.


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## Indecision (Oct 24, 2010)

Don't do it. All of your other accessories are designed to function at specific levels, like idle, they are not designed to move enough coolant or produce enough electricity below idle because the car does not run there. It's a waste of money, you might pick up a couple horsepower if you are lucky. Put your money elsewhere.


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## dustyminpin (Jun 19, 2006)

:agree I'm sure they serve their purpose, to a limited degree. But knowing what they do and how they function, they just scare the hell out of me. My speed shop asked me why I bought the SFI approved heavy duty harmonic balancer from Summit Racing which was the standard O.D. and not the u/s one. I told him that he could have those extra 3-5 horses and I'd keep my dashlights. 

The reason I swapped the pulley out was because the stock one is known to wear and wobble, causing belt wear and an unnerving squeeling sound. It happened to my buddy's Lingenfelter C5. I had read about the problem on C6's and Goats on other forums as well. It was one of those "hey while you're in there and everything's torn apart" kind of deals. It only cost me 200 bucks and looks better as well. Bright shiny finish compared to the cast iron look of the stocker.


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## Poncho Dan (Jun 30, 2009)

Lightweight pulleys would be the better option.


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## BRZN (Jan 31, 2011)

Got one on my car, no problems for 8,000 miles still have original battery.


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## youngGoat (Aug 14, 2010)

Has it made a difference performance wise on your GTO?


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## Mike_V (Mar 10, 2006)

I can say you will not know it's there. I see about 13.5 volts at idle and am also on the original battery. Just like lights are made brighter than required just to be on the safe side, the stuff under the hood spins more than needed just to be safe and work when in less than good condition.


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## BRZN (Jan 31, 2011)

youngGoat said:


> Has it made a difference performance wise on your GTO?


I didn't do a dyno comparison before and after it's install so I can't say for sure. It allows the accessories to spin slower so they aren't robbing as much power as with the stock pulley. Agree with Mike_V, you'll never know it's there. At idle the volt guage shows 14.5 volts and my lights never dim.


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## 87GN06GTO07IRL (Aug 10, 2009)

You'll be fine with the pulley. At idle i put out 14 volts. As far as cooling goes, i couldn't tell you. I user a 160 degree thermostat and never get above 185. Fans are set at full speed at 180. The true benefit comes from the reduced weight. Less rotating weight is always good. Plus when you take weight off the snout, it eases pressure on the front crank bearings.


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## Poncho Dan (Jun 30, 2009)

06gtoin216 said:


> You'll be fine with the pulley. At idle i put out 14 volts. As far as cooling goes, i couldn't tell you. I user a 160 degree thermostat and never get above 185. *Fans are set at full speed at 180.* The true benefit comes from the reduced weight. Less rotating weight is always good. Plus when you take weight off the snout, it eases pressure on the front crank bearings.


You're running the 2bar custom OS?


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## motoristx (Apr 27, 2010)

I have an SLP Under Drive pulley. I had problems with my belt walking off the edges on other pulleys. http://www.gtoforum.com/f3/walking-throwing-belts-whats-going-26742/

you might see something like this if you change it.


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