jdhuegel1

I didn't come up with too much in my search...so, I'm just wondering if I should go with..(If I even can) a pulley set, to compliment the other mods I have (see sig). Are there complete kits? Like a kit I can retain my airpump? Or are all the kits for a removal of something somewhere? Would a main pully be beneficial? Thanks!

rx7will

iTrader: (6)

I personally dont like underdrive pulley sets for street cars, i rather have a fully charged battery. The only pulley i would use would be the one for the water pump.

YayeR

anyone really gotten 16-20 hp with the unorthodox full pulley set?

rxshun7

Greddy offers a pulley set to eliminate the smog pump. I have heard that you don't need the pulley kit if you find a belt that will fit without the pump in place. However, I heard that the size belt that you would need is hard to find.

Fd3BOOST

iTrader: (7)

Don't bother with the main pulley unless you have a lightened flywheel.

amp

iTrader: (50)

I run without AP and AC....
Havent had any problems runnin full load with my pulley set....stereo..lights..radar..pc925..fans

Blade7

what does the combination of the pulley and the flywheel do? beside the fact that there is more ophff.
less mass, lower rotation, blase blase.


thanks.

Mahjik

iTrader: (1)

Yes, there is a kit that will retain the airpump:

http://www.pettitracing.com/sections/Base_System.html

You really won't notice anything on the butt dyno, but if you have the money, every little bit of power helps. I've been running them for a little while with no ill effects. I don't know if there was any real power released by them as I added several things at the same time.

maxcooper

I have both a UR underdrive main pulley and some SR underdrive alternator and water pump pulleys. I don't have a big stereo or anything, and I don't have any trouble with battery charging even with a small 51R battery (or the Hawker PC680).

It does make some difference in RWHP, but it seems to be in the 10-15 HP range from the dyno charts I have seen. 3% is said to be about the lower limit of "butt dyno noticable" power differences, so this is right on the edge.

The Unorthodox Racing (UR) kit only has one underdrive pulley -- the main one. UR says that most of the improvement comes from reduced pulley mass, and I have no reason to doubt that is true for most applications. On the RX-7, however, the stock pulleys are pretty light (the stock PS pulley, for instance, is much lighter than any aftermarket pulleys) so it seems clear that most of the power increase comes from underdriving the accessories.

If you get a small main pulley, you should get some bigger alternator and water pump pulleys to maintain some belt contact with the air pump removed. SR and GReddy both make larger (underdrive) water pump and alternator pulleys.

For the main pulley, the UR pulley is very nice, but it replaces the stock main pulley hub so it is harder to install. It is also easy to botch the install (as I did) and screw up a bunch of other stuff (see http://www.mazdatrix.com/faq/pulley.htm for details). The main pulleys from Pettit, SR, RX-7.com and perhaps others bolt to the stock pulley hub, which makes for a much easier and less error-prone install.

I am switching back to the stock main pulley and water pump pulley to get some more cooling system flow in preparation for running Evans NPG+ coolant. The stock main pulley will also increase belt contact on the water pump pulley with the air pump removed. In general, though, I think underdrive pulleys are fine for the car and do offer some additional power at the wheels without messing up the battery charging operation.

I already have a buyer for the pulleys I am removing, so please don't bother to make offers. If it falls through, I'll post them in the for sale section later. I am way behind schedule to make the change already, so I don't know when I will make the switch.

-Max

NCsublime

Think of the pulleys in terms of merry-go-rounds. The larger (in diameter) it is, the harder it is to start and stop. Also, the more massive it is, the harder it is to start and stop. Why? Heavy+large diameter=large moment of inertia. Therefore, by lightening the rotating mass, and reducing its diameter, you are proportionally reducing the moment inertia of the pulley. This allows for quicker change in angular velocity.

slipperyslater1

Check SR motorsports, they have some nice set-ups and explanations.

johnchabin

iTrader: (2)

I have had a main underdrive pulley for 25000 miles. My windows go up more slowly at idle. Battery holds a charge no problem.

BDoty311

After I installed my underdrive pulleys I didnt notice much on hard acceleration, but rather in normal driving. My speed kept seeming to get away from me and it was strange to have a mod that effects the entire powerband.

t-rex7

From what i've read, at 6,500-7,000 rpm the water pump spins so fast that it doesn't pump rather it churns the water. The aftermarket pulleys acutally solve this problem.