gottacatchup

I've be looking into my next modification and i've narrowed the search down to an Underdrive Pulley specifically from Unorthodox Racing. It seems like a good deal, approx. $200 with shipping is the best price i've found.

So my question is does anyone else have any experience with this produce or a similar one? Anyone have any proven power gains, i've read the description they give and they claim 5-8 bhp i believe. Anything i should worry about along the lines of massive engine failure from doing this?

And if anyone has any suggestions for alternate modifications i really dont want to spend more than $200 and i already have the basics, header, exhaust, intake.

juddz

I have an Unorthodox Racing underdrive pulley on my P5. You don't gain hp, so much as you recover it by reducing the parasitic loss in the accessory drive. Figure about 3hp, according to UR's own data. This might not sound like much, but remember that this "gain" is steady across the rpm range, even down low in the rpm range. Your engine might be making about 60 whp (under full load, i.e. wide open throttle) at 2,000rpm (I don't recall the exact numbers, but this is my guess). In that range, you can see that 3hp is a good percentage improvement. It's less significant at peak power, but you don't launch the car at peak power. Nor can you drive at that speed and load all of the time. Therefore, you will notice a pretty good improvement in how the car accelerates and feels by doing this mod. I highly recommend it. Just remember to use a torque wrench to tighten it down, don't forget the loctite, and shop around to find out which autoparts stores near you sell Gates belts. If you do not buy Gates belts, you will need to figure out which Goodyear or other belt part numbers apply to the new lengths you'll need. Oh yes, and I wanted to reassure you that after nearly a year with the pulley on, I have never had any charging or other issues (despite the much smaller diameter). Not even after sitting twenty minutes in stop and go traffic.

centsless

what about vibration dampening. The stock pulley absorbs much, but i don't know about UR's pulley would do the same. You really don't want all the vibration to travel through your drive line.
I'm not sure if what i said makes sense, its from what ive read about UD pulleys.

juddz

Vibration is no worse than stock...

slowpro

$200+installation should equal more than 3hp. not worth it.

juddz

As I explained, your car might be making around 60whp down low in the rpm range. In that range, 3hp is significant. At peak hp, it's not. But you cannot launch or run it all day at peak hp. When you accelerate, the engine has to pass through a broad area much below peak hp, where an extra 3hp can make a huge difference in how the car feels and reacts. You will accelerate through this less-than-peak hp range with every gearchange. That's why this mod improves acceleration and reaction off the line. My header is worth about 7whp or so, if I recall. And, I remember feeling a bigger difference in how the car felt off the line with the underdrive pulley, than with the header. It's also why I would believe that other mods that reduce parasitic loss to a greater extent (i.e. lighter flywheel) probably kick some serious ***. The numbers are misleading, unless you consider where you are gaining that hp. Also, a number is just a number.

Speaking from experience, I would say this mod is "worth it". If you disagree, please be sure to explain using either your experience with it or technical knowledge you may have on the matter.

juddz

[QUOTE=juddz] Also, a number is just a number. QUOTE]

I hate to quote myself, but I need to finish this thought.

A number is just a number, unless you understand the implications of it. Not every mod is a constant gain at every engine speed.

billzebub

Try the rr-racing.com underdrive pully. It's cheaper and does the same job. Well crafted, too. Rickman had one on his P5 before he sold it.

glyph_99es

if you are concerned about the harmonic dampener, based on some other threads discussing this in detail on the mazda forums, you won't see any difference unless you do some serious horsepower mods to the car, like a turbo, or supercharger. So you don't have to worry much about that.

goldstar

Of course underdrive pulleys DO NOT and CANNOT increase the BHP developed by your engine. You will experience some increase in acceleration due to the reduction in weight and even more so, inertia, due to the smaller pulley diameter.

There are only three ways to increase the BHP output of an engine:
1. increase the thermal efficiency
2. increase the volumetric efficiency
3. decrease internal engine friction because Indicated HP (the HP produced in the cylinders by the combustion process) minus the HP used to overcome internal engine friction (also known as friction HP) equals Brake HP.
IHP - friction HP = BHP

As you can see, changing to a lighter, smaller diameter pulley neither increases thermal or volumetric efficiency nor reduces internal engine friction. Therefore, underdrive pulleys have NO effect on HP. the fact that a manufacturer claims a HP increase does not make it true.

Da P-Funk!

Wouldn't the lower rpms of the accys translate into reduced (external) friction? Which must affect BHP through reduced parasitic friction....

goldstar

Yes, you're quite right there. If you reduce the power drain required by some of the engine accessories, net BHP will be increased. In the bad old days of the muscle car era, auto makers would engine dyno their powerplants with all accessories removed or disconnected and with low restriction exhaust collectors and air intakes totally unlike those that would actually be used on the car. This practice yielded the SAE gross BHP rating that became the basis for the "advertised" HP figures that manufacturers claimed for their cars. These gross BHP ratings were completely worthless since they bore no relation to the performance of the engine when actually installed in the car. Fortunately, that practice was stopped and today all published and advertised BHP ratings are SAE net, derived from engine dyno tests with all accessories in place and the 'in-car' exhaust and intake systems in place.

My point was that power pulleys, by themselves, do not increase the IHP of the engine and therefore any net BHP increase is purely a function of reduced accessory drive. Since the alternator, water pump and PS pump are not removed, only slowed down, any increase in net BHP output will be marginal, at best. IMO, as I already stated, any increase in acceleration is more a function of a lighter and smaller diameter pulley reducing inertia effects rather than any HP increase.

In contrast to power pulleys, it's interesting to look at the effects of other mods that actually increase IHP. High compression pistons will increase thermal efficiency and such mods as improved air intakes and exhaust systems and cams with greater duration and overlap will increase volumetric efficiency.

Those interested in installing power pulleys might want to check this out:
www.msprotege.com/forum/showthread.php?t=108915

Reference:
www.info-pedia.net/about/horsepower

juddz

Oh, and it looks cool, too.

meGrimlock

do these pulleys also reduce the output of the accessories like the a/c, stereo, etc? ive started to look into an underdrive pulley too, but i'm also planning a big stereo upgrade. thanks
-meGrimlock

juddz

I have been running a self-amplified subwoofer (about 100W RMS) in my car for about a year now, and no problems with the underdrive pulley.