Underdrive pullies

[Guest Z-rific]

Seems like a cheap mod to eek out a few more ponies.

 

Anybody have pros/cons?

 

I'm just running water pump and alternator. Thought I might try it.

[love-my-V8-280Z]

I'm no expert but I would not do it. I believe you will gain a few HP's maybe, but I don't think its a gain worth the dollars.

One thing two, don't you think the motor manufacture would have install a smaller pulley if it increased the HP?

Something get popular and they are all gimmickry

...

[blueovalz]

I'm using an UR underdrive on my 240SX, and found that it did indeed make a small difference. It was comparable to a hard pull with the A/C turned on verses turned off. That's about the difference the pulley made in the SX motor. One other bennefit I see is the reduced rpm beating on the water pump, alternator, and AC pulleys. Perhaps this is one reason I've gone 196K with only a change of a water pump. It did not reduce the effectiveness of the A/C, nor charging, at idle as best as I could tell. Mine was was a 23% reduction. The only challenge to it all was finding a correct set of belts to use on it.

[Guest Z-rific]

It looks like I can get a set from Summit for under $90. 25% reduction if I remember right.

 

Maybe I'll try it and let you guys know. My dyno will have to be the old "seat of the pants" dyno.

[BrandonsZ]

You can do this, and as long as you don't have any trouble keeping your battery charged, or keeping the engine cool, you'll have more power.

 

Alternator

 

The honest truth is you have enough power from the alternator at 2-3000rpm, so as long as you are 2000+ you aren't gaining anything significant for electric power. However this pulley has mass and takes torque to ramp up to speed, and similar to when you put a lighter flywheel your responce time will increase by an infinitesimal amount with a reduced pulley. (go aluminum of course). The alternator drags on the belt only if you are using electricity, so when you turn up the bass on your 1000W amp and turn on your lights during a rain shower with the windshield wipers going and you are rolling up your windows and draw on the alternator will be as much as you are ever going to get whether the pulley is going 2000RPM or 10000RPM. So the return on this investment is rather low.

 

Water Pump

 

You need a water pump to pump water through your block to keep your engine cool, and the higher the HP output the more heat it creates, so you might think a higher volume at higher speeds would be good? Not really since higher speeds will increase airflow through the radiator which increases efficiency and therefore the volume flow only has to be enough to keep from overheating the engine. There is a point of diminishing returns with flow volume vs. heat loss, However, the pump is constantly pumping and the force required to pump increases as the speed pumping increases. If you really want to save power, put a motor on the end of the water pump and drive it with electricity. Get one that's adjustable and you could even turn it off with temperature sensor control. Or you could "dial it in" and leave it at one speed that will work in all conditions all the time. Remember the power only robs from you when you use it.

 

Reducing the water flow by reducing the pulley WILL give you more power in some cases, but if your engine gets too hot, it'll rob your power. and of course you don't want it to overheat.

 

Also, take off that dang flex or clutch fan and put on electric ones, they'll save you power and actually regulate engine heat better depending ont he temperature of the day and the driving style of the driver.