grande

my question is about the underdrive pulley's benifits? my rx has full exhaust with header, i was wondering if anyone has seen a significant increase in horsepower that was put on the road? i'm curious to know, because i would like to get more horse out on the road not at the flywheel, and i was wondering if i will see a big change in power? is it worth it....how much of an increase would i see?

Evil Aviator

They aren't for increasing hp, they are for operating your alternator and water pump at the proper speed when the engine is at high rpm's. If you have a bridge-ported or peripheral-ported engine on your race car, then you need these pulleys. For street cars, these pulleys are just for show, and your accessories will not operate to their full potential, which means less coolant flow and more strain on your electrical system. Yes, you will get about 2-3hp at the flywheel, but I don't think it's worth it. Also note that it is possible to ruin your engine when installing the pulleys: http://www.mazdatrix.com/faq/pulley.htm

If you want more power, I recommend an aftermarket EMS and street porting. Weight reduction will also do wonders for your acceleration times.

grande

how much does street porting usually go for?

rico05

Anywhere from $300 to $1k depending on the port/size/who does it. Remember: The engine has to be ripped apart to do this, so it really isn't worth it unless you are prepared for the $1500-$3k for a full rebuild.

NZConvertible

A couple of hp tops. Underdrive pulley are for race cars that spend most of their time at high rpm. They don’t need much charge from the alternator and high rpm causes the stock pump to cavitate. On a street car, where most of the time is spent at low-mid revs, water pump cavitation is not a problem, and the stock alternator is crappy enough with out slowing it down and making it even worse. Save that money for something worthwhile. More power at the flywheel means more power at the wheels. Can’t have one without the other.

Evil Aviator

I think what he is getting at is that a 2-3hp gain at the flywheel is more like 2hp at the wheels, which makes the pulleys look even less impressive.

HuggyBear

well considering that the rotating mass ect. that is robbing HP is the same(flywheel, drivetrain ect.) before and after the pully install, 2-3HP at the flywheel is gonna be 2-3HP at the wheels..... conservation and all that scientific stuff ya know.... its not gonna be less.

NZConvertible

Yes it is. You can't avoid drivetrain losses.

Evil Aviator

Oh, so the drivetrain loss is a constant now instead of a percentage? How about FHP, is that a constant now too? Geez, why doesn't anybody tell me when SAE changes these things!

Amur_

I realize that this isn't what you asked for, but here's some more reading on the subject...

http://home.earthlink.net/~burntoast/powerpulley.html

http://reganrotaryracing.tripod.com/unxhoror.htm

--quote from the home page of the above link: "Shane Racing Main Underdrive Pulley. Horror stories with installation (Click here to see what can happen if it's not done properly. Be warned it ain't pretty) of the Unorthodox underdrive pulley convinced me that to avoid any possible headaches the simpler bolt-on pulley would be the way to go. There is, however, the very nice 4 piece set sold by Unorthodox for $399.00"

--------------------------
? RP Main Underdrive Pulley

The RP underdrive pulley is designed to reduce the ratio of revolutions of 'parasitic components' to the eccentric shaft. This particular unit reduces rotation of the alternator and water pump by 15%, thus allowing the power normally required to rotate that extra 15% to be available to the wheels. Also claiming it helps reduce water pump cavitation at high RPMs.

Pros-

With this mod, I noticed the engine revs a little quicker and high end accelleration was slightly better.

Cons-

The main pulley bolt in the eccentric shaft is nearly impossible to break loose with standard methods. This bolt must be removed to replace the pulley. Use a 3/4 impact , or a 1/2 breaker bar leaning up against the fender well and crank the starter just a touch.
-------------------------------------------------