I just got my racing beat cat back system installed the other day, and while waiting for my mechanic to tally up the installation bill, we began to talk about other mods I have planed. The conversation turned to the main drive pulley. He didn't go into detail, so my question is do I need to consider this mod? According to RX-7 store.com, adding the Unorthodox pulley will add 12 to 16 H.P.!
Why is this so? What gets disconnected if anything?

 

I bealive the Pulley's are smaller in Diameter, so the engine does less work to turn them, and acually prevent cavitation on alternator (or water pump, i got really bad memory)

EDIT: Ohh i c you mean Main drive pulley, *thinks* i dunno how that would give you more HP, maybe it is smaller in Dianmeter, so less power is used to turn it and engine accesories.

 

water pump...

 

So by geomertry, the pulley will "free up" more horse power. Is that right?

 

This mod doesn't even really add any hp, you see your engine alone makes just so much horse power. When you start add accesorys like alt. and water pump or even smog and power steering pump you start taking useable hp away from you tires. The small dia. pully just helps free up that lost power by using less of it to use your accesorys. Hp statements can be very missleading, but you could really see those kinds of numbers with that mod if you have ac, ps, alt, water pump, and a smog pump.

 

lol, atleast i was honest, and omitted that i was not sure.

Like i siad bad memory, ,to much Smot Poking in my past.

 

LOL

 

The purpose of the underdrive pulleys is to allow your belt-driven components to operate in their correct rpm range when your engine is run at higher rpm's than the factory intended. A side benefit is a little freed-up horsepower, but it is very minor. The problem is that your belt-driven components will operate much worse at lower engine rpm's. This means that when the engine is at or near idle rpm's in heavy city traffic, the water pump may not be able to cool the engine properly, and the alternator may not be able to keep up with a high electrical load (ie headlights and big stereo systems). The bottom line is that underdrive pulleys are absolutely necessary on high-rpm racing engines, but may create problems on a street car.

 

I wouldnt waste the $$ on pullies.

 

i second that. i race a 79 rx in the IT7 class. normally we'd only be able to rev to like 8k or so, with the RB drive pulley, temporary visits to 10k is ok. mostly cause the alt. can't take anymore revs. with the old pulley, but with the pulley, the motor becomes the limiting factor. who in their right mind want's to rev a 12a past 10k.

Craig

 

Under-driven pullies are a waste of money if you are driving on the street.

Stock is better I always say. (Although I found a dual alternator pully made that is not under-driven...I am ording it soon).

 

i'm gonna get that pulley too. rather than taking my smog pump completely off, i'll just remove the belt and put the dual alt. pulley on.

Craig

 

Put it this way. I have a 87 base. When it rains and I have to run headlights, rear defrost, defroster, wipers and stock radio my 70 amp alt can't keep up at idle. My alt is less than 2 years old so it's not bad..

I am going to install an aftermarket stereo and I am swapping out for a FD alternator once I find one AND I have the cash.. hehe.

I can't imagine decreasing power to the alternator..

Also my FC gets hot enough without slowing down the water plump...

 

I wouldnt be completely opposed to that....