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quote:Originally posted by Cal Cruzer
There is very little rotional mass in pullies. You will reduce rotational mass with a lighter flywheel that can be measured in pounds, but with pullies were are talking ounces. No, parasitic loss is what the smaller pullies address. The engine just does not have to work as hard turning these items.
This is just a snippet from a very simple search on the subject.
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quote:Underdrive Pulleys
For nearly 15 years, underdrive pullies have been one of the most popular performance upgrades for 5.0-liter Mustangs, and as soon as the modular 4.6 engines appeared on the scene in 1996, underdrive pullies were again one of the first readily available modifications. ItÂ’s a known fact that underdrive pullies reduce the parasitic drag on engines, which frees up horsepower that can be delivered to the rear wheels. Certified tests have shown that underdrive pullies can free up as much as 8 to 10 horsepower on 4.6 modular engines
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You can read the entire text here: http://www.modularpower.com/tech.html
or another article here: http://www.sportruck.com/howto/highw...rive%20Pullies
I will be willing to read any research on the subject that specifies gain from reduced rotational mass of underdrive pullies.
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Unorthodox Racing Ultra Street (Ultra S) lightened under drive crank pulley. Made of lightweight Premium U.S. made 6061-T6 billet aluminum to ensure consistency of the material's strength and balance. Every pulley is inspected multiple times from machining to anodizing to stocking and finally at shipping time. If at any point a pulley does not pass inspection it is pulled from production. An average of 5 to 12 HP and 4 to 8 lbs.-ft. on normally aspirated engines and 8 to 16 HP and 8 to 18 lbs.-ft. on forced induction engines. Higher gains are possible. For example, a Nissan 300ZX twin-turbo saw gains as high as 37 HP and 45 lbs.-ft. on the dyno just buy replacing the stock crank pulley with the Ultra S lighted underdrive crank pulley. Power gains are obtained in two ways. First, and most important, is the weight loss. An average of 2.7 HP is gained from every pound lost off the crank shaft. 85% of our gains are from weight loss. The rest of the gains are from underdriving, which accounts for about 15% of the total gains. Underdriving is not pushed for two main reasons. The main reason is to keep charging systems, air conditioning, power steering, and water pumps moving fast enough for every day driving. Second, not much horsepower is gained from extreme underdriving. In most applications all of the underdriving is done with the crank pulley, not the accessory pulleys. This is done so maximize weight loss can be achieved at the crank where most of the horsepower gains are found.
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PT powered PT with:
Fully built HRC Turboed 2.4: Wiseco pistons, T2 rods, Port & Polished head (Bob Special) with oversize Stainless Steel valves, #14 Crane Cams, AF/X UDP, No balance shafts, Custom 3\" downpipe, 3\" hi flow exhaust, Ported GT intake manifold, Bored Throttle Body, 30 lb injectors, Water/Alc. injection
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