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Old 09-11-2011, 02:19 PM   #1
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Under drive pulley to buy or not to buy

Should I get an under drive pulley? I am doing a cam swap soon and am on the fence about getting one.

I know the positive is a little more HP and torque. What are the negatives? Money is not an issue for this item.
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Old 09-11-2011, 02:40 PM   #2
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Hell, if money is no issue then by all means grab yourself a blower instead! In the past, my experiences have shown that with the UD pulleys the charging system takes a step back. With that being said, I think the later model vehicles don't have this problem. On my 95 full size Blazer I had one and it wouldn't charge for shit. But on my 06 Trailblazer SS is was fine. I say do it then if and when you upgrade you could always sell it.
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Old 09-11-2011, 03:32 PM   #3

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most people never have any problems with it, but to me it is not worth the 4 hp, to sacrifice the systems. the power steering has less flow through the cooler, but it saves it if you are doing all high rpm driving. the ac wont kick on until you hit 1500 rpms, and some people have dead batteries about once a year. on high rpm driving the cooling system will be dying.
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Old 09-11-2011, 06:25 PM   #4
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I bumped up my idle by 150rpm, and that helped the charging.

My MPG on the highway increased by a noticeable 1 mpg.

I don't know about HP, but it is a pretty standard mod once you're trying to squeeze the last drop of HP out of it.


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Old 09-11-2011, 06:47 PM   #5

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An underdrive pulley is a good 5-10HP mod for the long as you do it with a cam. With the cam, you have to take the pulley off anyway, so it is easy to change when you are there. I would not do it, just to do it though because getting the pulley off is hard, and takes a lot of time. As far as driving everything slower, I have run them on a few of my own cars, and have never notcied them. Just like stock. It would be different if you have a lot of electronics or big stereo.

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Old 09-12-2011, 09:01 AM   #6
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A couple automatic guys have had charging errors from the lower idle they run from the factory. I see no way the LS3 cars would have any charging problems at all. We've installed probably 30 of them with no issues here. Typical dyno gains from a underdrive pulley is 8rwhp.

We stock the TSP system & can ship asap!
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Old 09-12-2011, 03:22 PM   #7
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The 25% loss in charging can be offset with a 25% increase in idle speed(~150rpm), so I definitely believe it is a good bang for the buck item and highly recommend it with a cam install.
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Old 09-12-2011, 03:32 PM   #8
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If your pulling the car apart for a cam install, I would do it as well. Generally speaking we have seen 4-8 hp at the rear tires from it. While that might not seem like a lot, it can mean the difference from 492 rwhp to 500 rwhp...which for most is a big step.

Given the car is going to have a cam in it, chances are your idle is going to go up anyway...I would not worry about any charging issues.
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Old 09-12-2011, 06:28 PM   #9

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Yes you should. It's a no brainer if your already in there to install a cam. You will never know it's there once it's installed, unless you put a monster stereo in your car.
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Old 09-14-2011, 07:47 PM   #10
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I was in the same boat as well. I just did my cam package and did not do it. It will prob be all good, but I was just a lil paranoid about it..
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Old 09-14-2011, 08:01 PM   #11
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I experienced no negative side effects with the UD swap, enjoyed the increased torque (especially coupled with my CAI intake, ADM scoop and Vmax TB) and since you are performing a camshaft swap anyway, by all means install the UD pulley.

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