Looking at some underdrive March Power/Amp series pulleys. Question is, are they worth it? All the pulleys are smaller than the stock units correct? Anybody got any track times or dyno numbers with it. Thanks for the help.

I read an article on ChevyHiPerformance.com about these (too lazy to look it up, but it's on there) and they got a dyno proven 15hp on a fox body stang, which leads me to believe that you might see simliar results on a car like ours. They also did tests with other cars and found it to knock off a 1/10 of the 1/4 mile, and about 1.5mph. If you can pick up a used set for cheap, then it's a steal imo.

they work! make sure they are made out of aluminum for the most bang for your buck..... less weight.. if the alt pully is bigger than your stock pulley dont use it if your just driving around a lot.. your batt will be dead fast .. I run the SLP crank pulley only..

yea, well, i have a 383 HSR, heads, cam, so, you think they will help out more than a stock engine?

Hmm, well, since you are making substantially more amounts of power than a stock engine, your results may not be as good as a stock motor. The thing with pullies is that the accessories are a drag on the motor, so all you are really doing is freeing up lost horsepower. Since your engine puts that amount of power out, it leads me to believe that it's not having a hard time turning those accessories to begin with, meaning your gains wont be as noticeable.

That is just my theory though, lets see what some of the other guys think.

I just got these particular March pulleys (GM amp series) for my 136k mile LB9 5spd Formula and at the same time did 1.6 Summit roller tip rockers and new valvesprings. Hello! Definitely perked up the car.

What is the difference between the power/amp set and just the regular set. If I do not have a huge stereo, would I need the power/amp ones? I am guessing they modify them for big stereos and do not let as much power loose as the regular march underdrive pulleys.

I have the regular March pulleys on my 3rd gen road race car - it does not have to run headlights, tunes, etc. Your street car does, and I think March designed these pulleys for street cars. I have head too many complaints from folks using the regular ones about headlights dimming, etc. I am very happy with the amp series on my street car.

Sean, March CLAIMS that with the Power and Amp series you will have full power at idle (whether you want to believe that or not is up to you). For street use, it would probably be better to go with the power and amp series just to be safe. Or you could go with the ASD underdrive pulleys which tell you at exactly what RPMs you get a full charge (750 RPM, 900 RPM, 1000 RPM, etc.)

Also, to the thread starter... there was an article on gmhightechperformance where they put March power and amp pullies, an edelbrock catback, and a jet chip on a 5.7 TBI chevy truck and it gained 21 RWHP. I know the SBC chevy trucks are alittle different than our f-bodies but catbacks dont yield much, and everyone who uses a off the shelf chip seems to get slower, so that leads me to believe that the pullies were responsible for a good portion of that.

EDIT: It seems they added an intake to that truck as well. So that might be some of the gain right there. But i would still think the UD were atleast 5 HP of that gain...

So I guess you get better power from the regular pullies, but the power/amp series dont give as much power, but make it safe for the street.

I have a March Power set on my 305 TBI, its a crank pulley and an alt. pulley. The crank pulley is significantly smaller than stock, very light too. The alt. pulley is larger than stock but is twice as heavy as stock. To make for the difference I guess.
At and idle of 700 rpm I have a voltage of 12 volts, and can push a 1000 watt amp with no problem. I really noticed a difference shifting into 2 second gear also. I like mine, hope this helps.

On my G20s 305, I used a crank pulley from a 4.3 astro that bolted on fine and was about 5" in diameter compared to the stock 305s near 7". The lights dim slightly at idle, but I don't have any charging problems at idle either. Dual A/C, stereo, electric fans, etc, but I have a 130 amp alternator. There is a noticeable power difference, especially on a Hot summer day with the A/C on, fuel economy improved some as well especially with the A/C on.

So either way with either set ill gain just as much?

another chevy high performance or w/e magazine picked up some rwhp on a LT1 with the pulleys.. i dont recall how much overall but i think it was close to 10 if not over that on a mustang dyno.

dyno'd 218 stock... with catback, maf sensor tuning, cai intake, and pulleys, (could be something else but i dont have the article here with me) but those mods were good for a total of over 260rwhp on a mustang dyno

Yeah well... Hotrod magazines also dynoed the "Tornado" and said it increased horsepower...Dont believe everything you read...