Dyno results Underdrive pulleys


New Member
Aug 2, 2005
Anyone have just results from a dyon with the only change being underdrive pulleys? I am about moded out as far as bolts-ons are concerned. I would like to add a cam but the prices are to high right now. Thanks
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no dyno sheet, but the engine revs MUCH faster now. very noticable gain on my car. even my wife noticed the difference the first time she got in. :)
i didnt look at the mileage, but i think only about 1000. give the thread a few days and others will chime in with more miles on the clock.
Get the pulleys!!! I was worried about the negative effect on the water pump, but since I am running the 4.10s that turns her a little faster to compensate.

+1 on the faster reving.
No timing adjustment needed. Dyno's have been from around 5-10hp and around 10lbs of tourqe if you google it and hunt for a while. I noticed a differance when I had Steeda's installed about 6 months ago. MM & FF's most recent magazine comes with a DVD on a 05 GT piece by piece install and dyno per part. They got 10hp on the dyno with BBK UDPs.
Besides, U/D pulleys don't increase HP ? they free it up by slowing down your belt driven accessories such as your water pump and A/C which have nothing to do with the computer's stock tuning files... therefore no computer re-flashing is necessary.
A bump in idle speed is generally required to maintain alternator charging levels. Side effects of going with underdrive pulleys include:

Reduced A/C output in low speed driving
Reduced power steering assist in low speed driving
Reduced alternator charging at idle

Bumping the idle speed UP will only reduce these side-effects. I've used the Steedas on my 4.6 2V for about 20,000 miles and eventually just went back to the stock pulleys.
Have you experienced any negative effects?

I did experience some negatives with them on a 95 Mustang GT. They caused my headlights to brown at idle and significantly contrbiuted to an overheating problem that I had when stuck in traffic. I realize that our cars are completely different than that Mustang, but can definitely see why someone would ask the question before purchasing & installing this mod.
Marine One:

You brought up an excellent point. On my 00 Vic (4.6 2V V8), the headlights did dim at idle and got worse when I had more accessories on at the time (HVAC blower, Air Conditioning, stereo, and turn signals).

I'm never going to try underdrives again in any vehicle, but that is just me. :SNSign: