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| Underdrive pulley? http://www.4g61t.org/forum/viewtopic.php?f=26&t=5193 |
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| Author: | The Ethereal [ Fri Sep 05, 2003 8:20 am ] |
| Post subject: | Underdrive pulley? |
Okay guys, now that we got a newbie forum, I may ask a beginner's question w/o feeling ashamed. I never fully understood the principle of an underdrive pulley.  How shall they give more hp? Are they those things that are used in autox to reduce cavitation of the water pump (by reducing its speed relative to the engnie speed)?
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| Author: | oletymer [ Fri Sep 05, 2003 3:45 pm ] |
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less drag on the engines acc. less rotational mass free's up power already there does not create power that is not there |
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| Author: | socrateez [ Fri Sep 05, 2003 5:05 pm ] |
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In principal its the same as lightening the flywheel. Less mass to turn. On the pulleys you also have the effect of ratios too. One thing however, less rotaional mass= less torque. But, rpm climbs quicker and more hp. |
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| Author: | Bill Spruill [ Fri Sep 05, 2003 7:38 pm ] |
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 Nice to have you. Well, your question has raised interest in the past, and I see that it still does. I'm trying to be helpful here and not critical 'cause I had similiar q.s in the past. Go to the search function here and crank in "underdrive pulley." You'll get a whole lot to check out and sift through. Scroll to "UR al. pulley being tested" (the thread is somewhat backward, but you'll get it.) and "underdrive pulley." There is a lot of interesting stuff there. Go to Unorthodox web site. They sometimes have some "garage" sale items. Good luck Bill Spruill, oldest Colt
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| Author: | 89 mirage evo [ Fri Sep 05, 2003 8:11 pm ] |
| Post subject: | |
its all physics. a smaller pulley has less inertia and as a result, easier to turn. also the smaller circumference spins the accesories slower, so less energy is required to spin them. |
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| Author: | kjmerkel69 [ Fri Sep 05, 2003 11:26 pm ] |
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Quote: ...also the smaller circumference spins the accesories slower, so less energy is required to spin them.
This is the true secret of the underdrive pulley: mechanical advantage.Think of a multi-speed bicycle. The front sprocket is the crank pulley, and the rear gear cluster and wheel (and, inherently, the bicycle itself) are all the belt-driven accessories. You're trying to get going in the highest gear (chain on the largest front and smallest rear sprockets), but it is difficult. If you were to shift onto the smallest front sprocket (install an underdrive pulley), getting going would be considerably easier. Shifting to the largest rear sprocket (installing a complete underdrive pulley kit) makes things easier still. |
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| Author: | The Ethereal [ Sat Sep 06, 2003 3:24 am ] |
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Hey thank you all! Bill, I'll search for "UR al. pulley being tested" when my hangover won't impair me as much as it does now. Edit: HAH! I took a look at this thread. Great, now I know!
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| Author: | Bill Spruill [ Sat Sep 06, 2003 11:01 am ] |
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What's this hangover stuff? It's not even October Fest yet.  Oh, and not to disagree much with a prior reply, but most manufactureres say that pulleys other than the crank gain advantage only from weight. Still, a slower water pump will have less cavitation at high rpm. Bill |
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| Author: | The Ethereal [ Sat Sep 06, 2003 11:44 am ] |
| Post subject: | |
I dislike the Oktoberfest - to many drunk and aggressive people. However, my hangover was due to "some" partying tonight....  You're right, a slower w/p won't have as much cavition, cool better at high revs and will live longer. Cavitation is the main cause why ships need a new er... what's that thingie called in English, propeller? ...every now and then. The effects of cavitation are comparable to engine knock. Is it possible to build such a pulley at home? I don't want to spend $$$ or €€€ for the stuff and shipping overseas. |
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| Author: | Bill Spruill [ Sat Sep 06, 2003 2:58 pm ] |
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 I wouldn't think so. There is a high degree of vibration, and some say that even after market ones w/o a dampener are subject to breakdown. (Check out Buscher racing - I don't have the site at hand- and I believe there was some issue on that raised here in the old threads.)
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| Author: | The Ethereal [ Sat Sep 06, 2003 3:33 pm ] |
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Quote: I wouldn't think so. There is a high degree of vibration, and some say that even after market ones w/o a dampener are subject to breakdown. (Check out Buscher racing - I don't have the site at hand- and I believe there was some issue on that raised here in the old threads.)  Thanks for the help! |
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| Author: | Bill Spruill [ Fri Sep 12, 2003 4:16 pm ] |
| Post subject: | |
| Check out: www.extrememotorsports.com This site has some info. on underdrive plus other interesting stuff.
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