Just wondering if 2 piece underdrive pulleys help at all? Anyone have before/after 1/4mile times to share?

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom cold air intake w/K&N, SLP airfoil, ported & polished plenum, TB coolant bypass,Crane AFPR (47psi),94 octane,Crane Extruded Alum. 1.6 full roller rockers, Timing set from 4*BTDC to 10*BTDC,MSD coil,MSD6AL, Holley 9mm Annihilator Laser shot 50 wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, SLP 1 5/8 headers,SLP catback,3:73s,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Street legal with stock throttle body, runners,intake manifold,cam, and heads. Coming next..9# Procharger!

 

If your car is a daily driver, dont do this mod. You will have alternator and charging problems. I know several people who did, and they removed the pulleys, problem fixed.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

I don't know about the hypertech pulleys, but I have the march 3 piece pulley set and they work great. Have never had any problems with charging either. You will notice a decrease in voltage when your sitting at idle, but that is normal for underdrive pulleys.

 

I got a 2 piece YEARS ago, but the alternator pulley was an "underdrive" not an "overdrive", so I only installed the crank pulley.

I don't have any charging problems, though if I get stuck in a rain storm, at night, with the front and rear defrosters on; the voltage will drop a littl below 13 while I am idling. Not a big deal.

BUT, on a basically stock motor, the gains are minimal. I'd spend my money elsewhere, like buy PROM burning equipment and start burning my own PROM.

The cost is not that much more, but you'll have a much better running car, able to tune it for a variety of conditions AND save some money on gas by either chosing when you want to run 87 vs 92 AND invoking "highway mode" for when you are on the open road.

BTW, when you get into PROM burning, you will quickly find out that a lower temp T-stat, relocated MAT and TB Bypass can be detrimental to performance, especially in cooler weather. (And I don't just mean cold, just cool is enough).