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Old 08-27-2004, 03:53 PM
Turbo Trans Am Turbo Trans Am is offline
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Default Underdrive/Overdrive pulleys safe to use?

I've been doing research on underdrive/overdrive pulleys and have a few questions. Firstly, what percentages would a daily driver (aggressive) want to underdrive their accessories? I have stock stereo, but want to upgrade in the future. Which pulleys should be overdriven and which should be underdriven? What is safe on an essentially stock vehicle? I haven't been able to find if there is a difference in performance (i.e. more hp to the wheels) based on the diameter of the pulleys, or if it strictly due to the fact that aftermarket pulleys are lighter, or both. Is it the fact that the accessories are being used less extensively by underdriving that causes performance increase, or is it the fact that the pulleys are lighter, or both? Which pulleys should be underdriven, and which should be overdriven in our cars? I have heard that you want overdriven pulleys on waterpump to promote better cooling. I already have a 160 degree thermostat. Would there be a benifit to underdriving the waterpump? Do you overdrive or underdrive the crank and what effect will this cause? I have heard that changing the crank pulley is dangerous because the stock one is the size it's for absorbtion reasons and that replacing it will cause damage to the crank. What pulleys do you all recommend? How much more hp and torque to the wheels should I expect from swapping out all of the pulleys? I know there are a million questions here. Thank you all very much for your time and help!
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Old 08-28-2004, 11:52 AM
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Keller Keller is offline
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Thumbs up Re: Underdrive/Overdrive pulleys safe to use?

So let me see if I have this right...you want to have a street-driven, high HP car with a big stereo with all accessories...and underdrive pulleys?

I don't think so.

Underdrive pulleys are used to gain *small* amounts of HP by slowing down the accessories. You _might_ get 10-15 HP on a good day, downhill with a tail wind by the statement at http://www.marchperf.com/underdrive2.html Of course they make a lot for the Mustang crowd. You also slow down your water pump and alternator, which are fairly cirtical items. With the thumpin' stereo you are after, and the larger fuel pump you might need, do you really want to tax your electrical system further? Just my view on things.

I'm not even aware if anyone makes underdrive pulleys for the TR/TTAs, so the whole question may be moot. I thought March may have at one time, but looking at http://www.marchperf.com/pg42.html#buick there is no sign of them. At least it doesn't say that system is an underdrive.

The only aftermarket pulley system I'm aware of is the RJC system. See http://www.rjcracing.com/RJC_Buick_P...__pulleys.html The performance gains come from less rotating weight. In total, 9 lbs of rotating weight are lost. Just like with a switch to a lightweight wheel, rotating weight is worth more than static weight.

In addition, there are ways to replace your A/C with an idler pulley. Not sure if you wanted to sweat during all the fun, too.
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Old 08-28-2004, 04:37 PM
Turbo Trans Am Turbo Trans Am is offline
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Default Re: Underdrive/Overdrive pulleys safe to use?

Great! Thanks for info. The RJC ones look sharp. ATR makes some pulleys for TTAs. There is no downside to replacing the stock pulleys with lighter weight stock size pulleys?
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Old 08-28-2004, 10:44 PM
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Talking Re: Underdrive/Overdrive pulleys safe to use?

I don't think it exhibits the best cost-to-improvement ratio. If there is some extra cash in your wallet you just _have_ to spend, want to go just a thousandth quicker and look better, and have nothing else to buy, these are for you!

Don't get me wrong...they are slick! But I would only do them while I had other things in process because of the amount of work involved to install them and the small potential gains. I plan to put on new A/C lines and a new radiator over the winter, and may put a set on myself.
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Old 09-09-2004, 08:00 PM
Heavytouring Heavytouring is offline
 
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Default Re: Underdrive/Overdrive pulleys safe to use?

the lighter stock size pulleys won't do as much for hp levels as they will with quicker rev up (read: quicker spool ) ... one of the main benifets of switching in example to say a lighter flywheel.. the lower ratational mass lets the assembly get to speed(rpm) quicker... in an extreme case like a super light flywheel ofcourse the lower ratational mass takes away from your low end rotating assemblies anertia ... which is why some of the smaller, lower low end torque, need to rev high engines with super light flywheels lug at low rpm pulls

that's all a mute point however considering the buicks sustantial low end torque, and the fact most still have the auto (flexplate not flywheel) .. the 9lbs off the rotating assembly will make a noticable quicker rev up helping boost more then it will help actual hp numbers
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