Imo000

6hp at what point in the graph? But regrdless you will not feel a 6hp gain on a 300hp car. There is at least that much variation on the dyno depending how tight the straps are. Sure there will be some gain with an underdrive pulley, the question is, is it statistically significan and more importantly, can you feel the improvement. If you can't feel it, what's the point on a street car.

sharkster

Well actually one thing we've always noticed with upgrading pulleys is the improved responsiveness. That doesn't translate on a dyno but even the factory does this with different pulleys on later GT3RS' vs GT3s Common trick. I think some of us try to get whatever edge we can sometimes

On our 3.4L Cayman one of the other side benefits was it helped reduce the power steering overheating issues at the track too.

6ta1

I respect you as you typically have good inputs on the forum, but there's no black magic here.

Your accessories rob ~25hp (10hp power steering, 10hp+ AC compressor, 5hp alternator). Your power steering pump has to put the fluid @ 400+ PSI, you can't compare that with a push lawn mower.

The underdrive pulley reduces the accessory speed by 20%. With the mad assumption that the hp loss is linear with the rotation speed of the accessories (certainly not exactly true), then you gain 5hp.

Bottom line, I have one on my car and I clearly felt it. If you want to call it placebo, fine, that was still only $200.

Ahsai

The underdrive pulley will probably save some power on the power steering pump (you get less steering boost) but for A/C and alternator, I doubt there's any saving. If the A/C compressor spins slower, it has to spin longer to achieve the same cooling. Same for the alternator, if it spins slower, more current needs to pump into the rotor to maintain the same power output, which requires more force to spin.

A/C compressor and alternator require fixed power at any point in time (depending of what appliances are turned on, and the cabin temp settting, etc.) so regardless of pulley size, they will rob same power from the engine.

Ernie J

Super User , we use a DYNO PAK dyno, each rear hub is bolted to the rear drive hubs of the dyno, there is no slippage. We came up with the underdrive pulley to reduce the power steering assit , heat from excessive pumping which not needed at constant high rpms when "racing". 6 hp is a safe increase for little money. The Cayman is raced at 4000 to redline. Reducing the water pump speed allows the water to pick up a bit more heat as the speed of the slowing coolant has time to pick heat. In racing small things add up.

KrazyK

Heck just take the belt off.

sharkster

haha there you go

sharkster

Just an fyi- yes these do come with the tool and instructions