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Old 12-02-2011, 01:29 PM   #1
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UnderDrive Pulley for 2.7

Hey, I just looked up under drive pulley's for the 986 2.7 engine. I could not find any.

The RSS is only for the 2.5L.
The Cheetah and Tarret brand does not say which engines it fits.

Does anyone have an under drive pulley on their 2.7? What brand?

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Old 12-02-2011, 02:44 PM   #2
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They all fit the 2.5, 2.7 and 3.2 engines.
I have the RSS in my 2.7.
Happy Boxstering,
Pedro
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Old 12-02-2011, 04:51 PM   #3
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Pedro.

Two questions for you. Would you have any reservations regards engine longevity / engine temps and an underdrive pulley?

Secondly, is it possible to get s shortened belt to suit cars without aircon - thinking about removing the aircon kit from my car.

Thanks.
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Old 12-02-2011, 08:01 PM   #4
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No ill efects, do a search for peace of mind. As a matter of fact I have an UD and love it.

Yes, you can get/use a shorter belt when deleting the A/C, see link below

HELPFUL HINT: What size serpentine belt to run when using an under drive pulley? - GSR Autosport Community
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Old 12-03-2011, 08:49 AM   #5
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Excellent info re the belt options. I thank you.
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Old 12-03-2011, 04:33 PM   #6
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Oh, one more thing - does an underdrive pulley make a noticeable difference to the steering assistance? I'd love a bit more weight / effort from my steering? If so, the pulley would be a must have for me.
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Old 12-03-2011, 05:00 PM   #7
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I never noticed any steering difference but I did notice a performance difference. One thing to check is AC efficiency if you use it a lot, I never did.
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Old 12-03-2011, 05:06 PM   #8
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Planning on removing the AC, too. Never use it. Rarely hot enough in the UK to need it. Even when it is, it's a nice change to be too hot for once!
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Old 12-03-2011, 05:09 PM   #9
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Planning on removing the AC, too. Never use it. Rarely hot enough in the UK to need it. Even when it is, it's a nice change to be too hot for once!
That is going to require a special belt for sure then, at NAPA you can get gates belts in small increments larger or smaller. With just the under pulley a belt change was needed. As long as you have it out, pop off the tensioner and rollers, the bearings inside come out easy and can be bought inexpensively and replaced.
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Old 12-03-2011, 05:40 PM   #10
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What about the best brand for power and weight?

I think Cheetah offers the most power because they say 20% reduction and 14HP increase at crank, which is better for power than 16% reduction for RSS and Tarret, am I right in saying this? I am not even sure.

RSS claims 7-8 wheel hp, not sure at crank)

I think Tarret offers the belt for free with their under drive pulley.

All are roughly $200.
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Old 12-03-2011, 10:19 PM   #11
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Garage
Sorry guys, but just because i love to be informed, could some one let me know where a UD pulley would go, and why you would want one? I mean performance gains, but why?
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Old 12-04-2011, 02:59 AM   #12
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Sorry guys, but just because i love to be informed, could some one let me know where a UD pulley would go, and why you would want one? I mean performance gains, but why?

The pulley goes on the end of the crankshaft, it replaces the current piece, a splined drive which matches the rubber drive belt. When you change the diameter of this drive, it changes the speed of all the pieces it rotates, like the ps pump, oil pump and AC. The result in reducing turning speed is to return power to the engine as the torque needed to spin everything is reduced. Think of using a larger gear on a ten speed bike at a hill. If you decide to use one know that the case needs to be altered and it's important not to destroy the threaded piece to be altered as it comes into play when doing engine work. One should trim it carefully only enough to accommodate the new gear, it's Aluminum and soft as butter. Lastly, the reduction variation may be for track versus daily driver, if you reduce the spin too much you are not charging the battery efficiently and AC I'm thinking would be horrible, the good news? You can actually feel an under pulley right in the seat of your pants.
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Old 12-05-2011, 09:42 PM   #13
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I am also learning here. Good info guys!
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Old 12-27-2011, 08:40 AM   #14
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I've scheduled to have the UDP installed at Mantis this Thursday... I hope it has zero ill effects on a daily driver beside A/C which I use maybe 3 times a year.

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