Think of under drive pulleys like the gears on a bike. The larger the front sprocket is compared to the rear sprocket the harder it is to pedal.The smaller the front sprocket is, the easier it is to pedal. The under driver pulleys reduce the size of your crank pulley(front sprocket) and it increases the size of your accessories like water pump and alternator( these are like the rear sprocket of the bike.) The pulleys make it easier for your engine to turn your accessories, freeing up a little horsepower.
Most of them all advertise a 15 HP gain. Its kinda hard to screw up a pulley, but I also like the March brand
In reality... You might get 7.
Food for thought: A couple of years ago I came across an article about underdrive pullies. The wheel output of the car was roughly 200 with the stock pullies and sperpantine belt installed.
Later, the removed the serpantine belt completely and powered the electrical system through a shop source to the battery. The total wheel HP gain on this particular vehicle was 5 whole HP. I wish I'd scanned and saved the damned article. Driving normal accessories took 5 rear wheel HP from the car.
Figure in underdrive pullies that are say.... 20% underdrive. On THIS particular vehicle, and you'd net a RWHP gain of 4. Ummm.... yay? The downside is that your electrical system is putting out less, your water pump is putting out less, the fan (if not electric), and every other thing you've just underdriven.
I'd LOVE to see a back to back dyno of a stock-ish Fox with OEM and then underdrive pullies.
Seat of the Pants feel to me means some 30ish HP at the wheels. Gonna get that from UD pullies? Not likely. I attribute most advertised gains from UD pullies mostly to ricer math.
Hey guys,I know this is my first post on here.I was an advid member years ago!!Anyways,I have to agree 100% that you will NOT feel a "seat of the pants" increase in installing underdrive pullies.In The 15 years that I have been fooling with thse Fox body cars,I have never said,WOW those pullies really made a difference.I don't want to discourage anyone from putting them on there car (all 4 of my cars have them).I just think (KNOW)that the manufacturers HYPE up the HP ratings drastically.If you can get a chance to go to a swap meet,That is the best place to pick up a set, of underdrive pulleys for as cheap as $15-$20 or less!!Hope I didn't step on any feet here!!!
When I did them on my LX, I did them with a bunch of other stuff, so I couldn't tell any specific gain. HOWEVER, I just installed them on my otherwise stock Saleen a couple of weekends ago. There was a very noticeable SOTP difference. Not huge, but noticeable. At some point this summer, I'm going to attempt to get it on the dyno and see what's what.
haha ok thanks guys. so with all that being said should i even put some on? im thinking about getting some but they they just seem like they might not be worth it? so to all of you that do have them what do you honestly think? should i get tome or is it not worth it? and thanks again for all your input
The pulleys make it easier for your engine to turn your accessories, freeing up a little horsepower.
Read this. They got an increase of 10 dyno proven horsepower with nothing but a pulley change, as well as better power across the powerband.
Underdrive pulleys. With many reports of quarter-mile improvements, we had to try underdrive pulleys on our
dyno Mustang. March Performance supplied their lightweight aluminum three-pulley "street" set, part number
2010, powder coated in a brilliant red to match our test 5.0, to reduce the horsepower-robbing drag from the front
engine accessories, including the water pump and alternator.
Steve bolted on the pulleys in less than 10 minutes, and the test run showed a peak horsepower number of 217.4,
an impressive increase of 10.1 horsepower, even more impressive was the fact that the underdrives helped across
the rpm band -- 5.2 horsepower at 2500 rpm, 9.4 at 3000 and 12.5 at 5000. The pulleys also improved torque all the
way across, with a peak improvement of 13.6 lb ft.
One side effect of the pulleys during the remainder of our test was the additional heat in the engine. Since the
underdrive pulleys slow down the water pump, the engine ran about one notch hotter on the temperature gauge
after a series of dyno runs.
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