Ryde _Or_Die

http://unorthodoxracing.com/mazda_rx7.html

RedFD

Wow i wish i had money!!!!!

Ryde _Or_Die

Ya I wish I had an FD, lol. But seriously I saw that and its like half off so I figured you guys might be interested.

jimlab

The GReddy underdrive pulley kit is about 1/3 the price, doesn't risk the internals of the engine by introducing harmonic discord, is much easier to install, and serves the same purpose... underdriving the water pump on dedicated track cars to prevent cavitation which can lead to air bubbles in the coolant and hot spots in the engine...

In other words, unless you drive your car at 6k+ rpm for long periods of time, it's a waste of money, and if you just have to have an underdrive pulley kit, do yourself a favor and save $200 by buying the GReddy kit. The pulleys are in different locations but the end result is exactly the same.

mjw

iTrader: (1)

Wow.. that is an insane price.. I might just have to get it because of that! Anyone running all the pulleys with their air pump as well? I don't want to disconnect my air pump but the pulleys are tempting.. just worried about finding the right belt size.

Matt

mjw

iTrader: (1)

Isn't the most power gain available from the crank pulley alone? On a piston engine I can understand the harmonic dampening that is needed, I would never run an UD crank pulley on a piston motor.. but a rotary? I need to do some research on this I suppose..

Matt

jimlab

They all perform the same function... under-driving the accessories. The main difference is that a crank underdrive pulley underdrives ALL accessories, the accessory pulley kits like the GReddy kit underdrive only the accessories on which the pulleys are installed.

The main benefit is saving the alternator and preventing cavitation in the water pump during long periods of high rpm use typically seen during track and road course events. There is very little power "gained" with underdrive pulleys unless you are reducing the number of accessories at the same time, thereby reducing parasitic drag in the belt drive system. If you're still turning the same number of pulleys, you're not "reclaiming" any substantial power, or in other words "freeing up" horsepower that you already had which is used to drive the accessory belts.

You are right, the underdrive crank pulleys are more of a risk on a piston engine, and less of a risk on the rotary, but the eccentric shaft bolt can be extremely difficult to remove while the nut on the alternator and four bolts on the water pump are very easily removed.

There's another thread on this subject already, which should explain everything if this isn't sufficient.

GoRacer

iTrader: (2)

I have a Greddy (2 piece)kit and it's only to bypass the air pump.

The Ultra SS is a 4 piece kit. This kit is intended to shave wieght off the pulley wheels, the same theory as light wieght forged racing wheels.

I don't mind being corrected if i'm wrong, but I don't beleive this kit's main purpose is to underdrive.

http://unorthodoxracing.com/ultrass.html

To bad the sale ones are only in black.

jimlab

By all means don't let me tell you how to spend your money or how to save it. Buy whatever pulley kit you want, dyno the car afterwards, and tell us all how vast your horsepower gains were.

Who am I to tell anyone anything? After all I only had the GReddy kit on one engine and the Unorthodox eccentric shaft pulley on another. Why should it matter what the real purpose of underdrive pulleys are when you can spend lots of money on shiny pieces of anodized aluminum to dress up your engine with and receive gobs of free horsepower to go with it??

I'll tell you this... if underdrive pulleys produce as much horsepower as the manufacturers claim, then it's the cheapest horsepower you'll ever find, short of nitrous oxide... good luck.