Pulleys.
 

I want to buy some pulley for my 8, but don't know if its a good idea. There are several companies that makes them and I'm not shure which one is the best for my car.

Right now I'm very interested on buying the shane racing power pulleys at www.shaneracing.com.

http://http://www.shaneracing.com/RX..._Kit6Large.jpg


Can any one help me? I'm not sure if its a good adea. Very interested on your comments and advices.

i've seen a couple of posts by people here saying that if they had the chance to go back and do it again, that they would not purchase underdrive pullies again, because they make almost no difference at all.

if you want to do something and get a few extra hp, go with an intake. look/search around ther performance mod section here to see opinions on the different options.

Unorthodox Racing and I would definitely install them if I did it again!

Mazdaparts.com has them for 250 shipped.

The Unorthodox pulleys look real nice too. I believe the complaints were with the SR Motorsports pulleys. I wish that $99 acorn nut for the alternator pully was more reasonably priced.

Well that sounds like a satisfied customer. 4 years to Supercharge, can you elaborate?

Are they so much lighter that you feel/measure some horsepower gain?

The pictures in your 2nd post look nice - do they stay clean enough under the hood to be a regular 'show-off' item?

Did you have a dealer install them or DIY? Any concerns about warrenty? I think they shouldn't be an issue, but I'd be interested to know what you've heard.

I would be surprised if the dealer would even notice the only one that is really in plain sight is the alternator pulley. They have to be looking for it, as in over the battery looking down.

They are lighter I was amazed by the difference they made in acceleration. It revs easier too.

I installed them myself. The toughest thing would be removing the alternator nut if a person does not have an impact wrench. With one it is a trigger pull and it comes spinning. Rest of them were easy to get at once the airbox is removed.

Thanks a lot for the info.

Can you post a picture of them install?

Here's some pics just took 'em with my PDA.

Freakin' worthless. Save your money and get a hi-flow cat. more hp gain. The pullies (I have the SR units) were not much lighter, if at all then the stock units. The stock pullies aren't 15 lbs., like on some V8's so you are not going to save much weight (hence make the engine more efficient) and the underdrive is only 20%.

Like I said earlier the ones that ^ complain ^ eh hem (fanman) have only tried the SR Motorsports pullies. :eyetwitch

I know he has warned many about the SR's.

Have you tried the UR pullies Fanman? :squint:

hes the get ur specializes in pulleys so they r good sr dont so they are bad theres more to just how heaxy pulleys are to make power

That said, high flow cat is good from SR Motorsports :) I had to heat up the hanger and put a twist in it just before the catback. It fit but it was right against the frame and I didn't want it resonating through to the cabin. I have that installed with the Greddy SP2.

:wallbash: :soapbox: Why do people insist on asking if the pulleys are LIGHTER??? The lightness or heavyness MAKES NO DIFFERENCE!!!!! It is the underdriving that counts. And you get every horse to your drivetrain that you stopped sending to your water pump/alternator/ac. Sending less rpms to your waterpump actually can be a good thing. :soapbox: :wallbash:

Pulleys do not equal Flywheel. Lightweight flywheel, good. Light pulleys, who cares.

If I have offended, I am sorry. That was not my intent.

That is not correct. The two ways you make hp with pulleys is you lighten them, and/or you underdrive them. When you lighten them, you make the engine do less work hence it is not really increasing hp, but it is freeing up hp. This is exactly the same principal as a lightweight flywheel, but in this case you are not talking about dropping a few pounds off of a 18 lb. flywheel (& counterweight), you are talking about less than a lb. That is why this doesn't work for the RX8. On a large V8 engine the pulleys are solid steel, and huge, and might weigh 15 lbs., and if you can drop off 6-7 lbs. that is a huge difference. Similar concept to underdriving it as well.

Understand that there is not much weight there to begin with Supercharge. It's different if one set of pullies is 15 lbs, and the other is 5 lbs, but the stock ones weigh about 2-3 lbs. as it is. You are talking about ounces. Second thing is the degree of underdriving them is not far off from the 2. UR is about 20% underdrive, the SR units I believe are about 15%-18%. The dyno claim of 9 whp is far fetched. I got about 1 whp on mine. If somebody has pulled off 9 whp, other than UR I would love to see it. So far, even in the RX Tuner magazine I have seen butt dynos, but as we all know those are notoriously inaccurate.

The difference in power that is required to increase the angular velocity of two disks equally with moments of intertia that, vary equally as a function of radius, that have radii of 0.25 feet, and when the two disks differ in mass by 25%, is miniscule (about 0.3 hp by my calc with rpm increasing linearly at 1000 rpm/sec) compared to the hp output of the engine. On the other hand if it takes 10 hp to drive the alternator and water pump (this is about right for an approximation) and you reduce the gearing by 25%, you get 2.5 "free" hp. Do you see my point. Difference in mass on this small of a diameter means just about nothing (differnent on a flywheel cause you have more diameter and more mass. You can get 10 hp by theory easy and you can also change I to bias the weight to the center of rotation) Do you see my point. The weight savings is insignificant (for non-race use)

When you are talking about a 1-2 hp gain, your example is literally 15%-30% of the hp gain. Obviously it's not going to give you the hp gain/freed hp of a flywheel. Especially for this application. On big engines, the pullies can be quite a bit larger & heavier, and they can make that application where they lessen the weight, but also because the diameter of the pully is larger, they can concentrate the weight towards the middle more as well (and I understand that concept as you look at a stock flywheel vs. the MS, and while the MS is only 1 lb. lighter, more of the weight is centered in the middle). In our application is is not very feasible.

Agreed.

This is the first I have ever heard of under-driving. Do I understand this right - the SR and UR pulleys have different diameters from the OEM parts and thus will transfer less spin or less power to the water pump and the alternator?

If I understand that right - wouldn't reducing the drive to your alternator be a bad thing in a cold climate? Wouldn't reducing the drive to your water pump be a bad thing in a hot climate?

It also has to do with ratios; if the crank pulley is smaller it changes both the amount of drive to the other pulleys but if those are smaller on the same scale the drive stays the same.

The size of these is considerably smaller. This gives gains like a figure skater spinning around with her arms out is not as efficient as spinning with her arms in.

As for cold climate I haven't had any problems and I live in Minnesota. It's been below zero numerous times this year already.

I've had SR's pulleys on for over 2 years now, and haven't had any problems in the heat of El Paso.

Your alternator begins DUMPing power after about 2000rpm. Also look up, cavitation on the RX7 site to see positive results with underdriven waterpumps.

I understand ratios, but to shrink the pullies like you are talking about you would have to have a new belt first of all (taking diameter away from a pulley, you would also need to get a new belt as it would fall off otherwise), which I don't think the kit has, and we are talking to get the effects that you are talking about you would need to take inches of the circumference of the pulley & belt. Our stock pullies are not that big to begin with. You are not talking big V8/V10 units the size of small pizzas, you are talking about pullies the size of hockey pucks already, so the size decrease is minimal at best. other than that weight shrinkage or centering of weight, look what carbon & I have stated about that.

Also if you are talking ratio change to a smaller pulley on one unit you are also talking about overdriving a component, that will lead to more wear & tear on a component.

Just to add to what Fanman said, to underdrive you either make the drive wheel small or the slave wheel big. Or a combo of both. Like on a 10 speed bike. To go slower you go into the granny gear on the front, and the sissy gear on the back. (I love bike terminology!!! translated it means small chain wheel on the front and big cog on the back)

Fanman I had to put smaller belts on. The kit doesn't come with it but they say which ones to get for it. :) Belts were only $15 for both.