Pulley Upgrades

Last updated: May 14, 1998


There are 4 pulleys on the 13B-REW (3rd gen engine):

There are several options as far as upgrading the pulleys with underdrive ones:

  1. Replace the main pulley. I believe this is what Unorthodox Racing's pulley kit does. I think Pettit's kit just has the main pulley too. New belts will be required.

  2. Replace the accessory pulleys (alt, airco, airpump). The Greddy kit includes at least the airco and alt, don't know about the airpump.

  3. Replace the main, the alternator, and the airco, and remove the airpump. This is what the Rotary Performance kit does, or you can buy the Greddy and Pettit kits and use together. (And possibly the Unorthodox kit used w/ the Greddy one.)

All of these options will require new belts, since the new pulley(s) will be different diameters. The new belts come w/ some of the kits, e.g.- Rotary Perfomance's. Ask to make sure. The exact sizes are listed below for some of the kits.

It is a good idea to measure the belt before installing so you will know what you need later when they need replaced. Or just keep the packaging labels from them if they came w/ them.

Also, you can just disconnect the belt for the air pump IF you have a midpipe and the main cat has been removed.


Date: Thu, 14 May 98 01:26:34 EDT
From: zgluszek@VNET.IBM.COM

I agree that if you run your engine close to redline, you will benefit from the water pump RPM reduction, but if you are stuck in traffic in Dallas, on a hot day..... you might appreciate being able to flow more while idling...

It is a matter of how you use your car. Mazda spent a lot of engineering time trying to optimize for the different driving conditions and matched the pulleys that way. They did extensive testing in Death Valley, on Alpine roads, in a city traffic and on a few race tracks.....

If I were running 1/4 mile only.... I would run modified electric water pump on FD....

If I was doing road racing or track racing and running continuously close to redline... and had the name Speed Ricer... I would go for the pulley set...... but......

The key to pulley design is to optimize it size for your driving style (average engine RPM) and for the outside temperature range... taking into consideration engine load, flow rate, heat transfer from engine, flow restrictions, thermostat operating range, radiator thermal efficiency and external weather conditions.... to name a few....

Can you guarantee that the MR "X" basement manufacturer did the homework, or just picked a.... let say 20% reduction in pulley size as a good target..... and then fine tunned pulley dimension to match the next available belt size... Most of MR "X" manufacturers jump on the pulley market to satisfy.... Rice Boy Syndrome.....

That is why you can buy a set of pulleys to match your nail color! ;)

I would never look at the main pulley, which is REDUCED in diameter.... Too small diameter of the main pulley induces the belt slippage during fast engine acceleration and thus forces you to increase the belt tension.... shortening the water pump life....

If I ever decided to play with pulleys I would go for a set which INCREASED alternator and Water Pump pulleys size.... A lot better way ....

It leaves you also with an option to use larger Alternator pulley and keep the water pulley intact if you so desire......

I am planning to use a larger Alternator pulley because I do not require full alternator output. You can get away with almost 50% reduction in wattage if you give up on the Air Conditioning and the boom box in the trunk..... I know this is asking too much..... ;(

BTW - I had a conversation with "One of the RX-7 Expert Tuners" .... / will not reveal his name without his permission / and he stated that the new aluminum pump was re-designed carefully by Mazda to move up cavitation as high as possible and it currentlly starts at around 7750 RPM, so....

I determined that the cavitation should not be a major excuse to have the engine matching my nail color.... :(


From: Steve Cirian
Date: January 12, 2000

The RP race pulley kit replaces all of the pulleys, but requires the removal of the airpump. Their underdrive pulley does just the main one.

When I was doing research for mine, Unorthodox used to just offer the main pulley replacement, but now it looks like they have a complete set (Ultra Street Set) that replaces them all and lets you keep the airpump.

Greddy (I think) does not replace the main pulley, but does all the rest. An old note on my site says that they also require you to remove the airpump. But they may have chagned thewir product since I looked at them last. One more key difference: According to Greddy's web site, they are "Alive with Power!" :-)

It used to be that you would use the Unorthodox main pulley, in conjunction with the Greddy accessory ones. The RP came out with the complete kit.

Pettit (while I am at it - might as well do the full rundown), just does the main pulley.

One key thing to look for is that they include the belts. Or at least specify which size you will need. Hopefully not a weird size that no one stocks.


From: Steve Cirian (steve@ScuderiaCiriani.com
Date: September 12, 2000

>My question is, which connections did you plug (and what did you use to
>plug them) in removal of the air pump.  I've got to figure out what's
>going on with my car soon or it's going to drive me crazy!

I haven't actually installed the pulley kit yet. It's a long story, but the short version is:

To install the pulley kit, I need to get rid of the airpump.

To get rid of the airpump, I need to replace the cat w/ a midpipe.

To replace the cat, I need to beef up the fuel system to be able to feed the engine w/ no back pressure.

To properly supply the new injectors, I would have to install a new computer.

I don't have the time to do all that. I suppose I could just get different belts and then put the pulley kit on w/ the airpump still there, but I just sort of put this on the back burner. Too many other projects going on now.

BUT... I would think you need to plug the line going from the intake airbox to the pump. Since you removed the main cat already, you don't need to worry about it. I can't think of any other lines that should be going into or out of the airpump. I don't have a diagram here handy (I am out of town).




Date: Wed, 07 Jan 1998 10:12:13 -0500
From: Terry Ferragame

Chuck Westbrook wrote:
>I've been looking for a kit but with the air pump still installed and
>being used. Pettit has such a kit but it is too expensive.

The Greddy kit requires you to remove the air pump (should only be done if a midpipe is used). As you're aware, Pettite sells an underdrive pulley kit.


Date: Sat, 16 May 1998 11:06:38 -0500
From: "Kevin Tan"

There are 2 belts on the 3rd gens, the following pulleys are covered by the two belts:

1) main crank, waterpump, alternator and airpump.
2) main crank, a/c and power steering.

If you eliminate your air pump, the belt you'll need will be a "4" rib 30"-31" (can't remember) simply because its rare to find a 5 rib belt in that size.

On the topic of the Greddy pulley, I have GREAT new pictures of what it replaces, In fact, the pics were taken with the whole assembly (alternator, water pump) off the car.

If you follow the main page, this is the route........Engine........Polished parts.

I realize that a number of you have not got javascript enabled browsers which is my fault becaause i made the mistake of using them in my links. I will change this soon by adding additional NON java-encripted links. Therefore the direct link to the pulleys on my page is :


If you need even more pictures of the Greddy Pulley all connected up, go to:


Also the polished pulley on this page is a custom made pulley that eliminates power steering while keeping a/c. Ignore that since most of your cars will only have a "pressure" type pulley that puts force on the belt. Besides that, the assembly should be pretty clear to see (the blue pulleys!)

Unorthodox Racing

Unorthodox Racing has a Web site. They have two options: a Race pulley that just does the main one, and the Ultra Street Set, which does most of them.


From: Drew Blair (Drew.Blair@billingconcepts.com)
Date: February 11, 2000

The UO Ultra Street set includes Main, Water Pump, Alternator, and Power Steering pulleys.

It's doesn't include the air pump or the AC because they have clutches.


From: Rich Spear (rdspear@hotmail.com)
Sent: Thursday, January 27, 2000 3:49 PM

I've already posted my experiences with the Unorthodox pulley (Dave at KD had to pull the engine bay apart to get to the front engine cover, which had to be replaced along with all of the bearings, spacers, etc.) and my recommendations (don't do it). Someone else posted their experiences and cost ($1600) after an Unorthodox install (I don't have the details).

Yes, it's specific to the Unorthodox. The other pulleys simply provide the outer portion that bolt to the main center of the existing pulley, which is at the end of the eccentric (drive) shaft. For the UO, the entire part is replaced, meaning you need to unbolt the main retaining nut of the entire drive train. When Dave at KD did mine, one of the spacers in the mechanical chain, and the associated bearing, slipped down about 1", because the retaining torque was released.

When it all bolted together, the engine turned, but instead of being concentric, the bearing and spacer were offset, with the edge of the bearing near the center of rotation (I can draw it better than explaining it).

About 200 miles into my drive home, I begen losing voltage (leaking oil on the belts), then the oil warning light came on. When I opened up, there was a small oil fire (quickly extinguished, luckily), oil everywhere (including the back of the car where it had flowed under the car and been sucked up by the vacuum) and I was 2.5 quarts low.

Dave towed it back to the shop, found the problem, and ended up taking out everything in the front part of the engine compartment, buying and replacing the front engine cover and gasket, replacing several bearings, spacers, the crankshaft counterweight, and a few other things. I still have the old parts - ripped up, charred from the friction heat and, in one case, a 2.5" OD, 1.75" ID, 1" thick spacer, snapped in half. Took him about 2 days to fix.

I was lucky - Dave admitted it was his fault and charged me nothing (verifying his reputation here, and the reason I went there in the first place). Another 'lister posted that he paid $1600 after a UO install, although I never got the details on the problem.

Just a word of warning from 1 experience. Again, Dave had done over 10 of them and never had a problem. He was replacing my clutch at the same, and thinks that maybe having both ends of the drivetrain loose at the same time caused the problem. I pass the data so all can make an informed decision.

Max Cooper has shared the details of his problems, which sound exactly the same, so it's not a one-off.


Date: Thu, 27 Jan 2000 22:59:25 -0800
From: Max Cooper (max@maxcooper.com)

I was the one who spent ungodly sums undoing the evil of my Unorthodox install. The problem is that the Unorthodox pulley, as nice as it is, requires removal of the bolt in the middle of the eccentric shaft. When you undo that bolt and pull the old pulley off, it lets the other stuff slide out a little and can cause the thrust bearing to become misaligned. My pulley wobbled for 5K miles while I rationalized that I just didn't get the key back in correctly. When I finally took it in to get the pulley and a big oil leak fixed, it cost lots of money. With the thrust bearing misaligned, the eccentric shaft was free to slide around and that ate my recently replaced rear main seal requiring removal of the tranny to install the $20 part. The front cover had to be removed also so that a new thrust bearing could be installed and aligned properly. I wasn't aware that the design of the pulley was responsible for this unfortunate condition, so I had the tech install another one (I chewed mine up with a gear puller getting it off). He was able to get the second one installed okay, and it is all fine now. In fact it is great if you can get it installed right ;-).

The bottom line is that I recommend against installing the eccentric pulley unless you can figure out some trick to avoid having the thrust bearing slip out of place. I have nothing against the pulley, in fact I think it is very nicely made and an excellent bargain at $180, but the fact that you have to remove the center of the old pulley to install it makes it impossible for me to recommend it. Felix's site has more info, and perhaps some insight into what tricks might work to ensure a good install without removing the front cover.

Oh yeah, and getting the center bolt loose is a MAJOR pain in the rear. Pettit Racing and Rotary Performance (Texas) sell safe-and-easier-to-install underdrive eccentric pulleys that bolt to the stock center.


Unorthodox responds to the issue of why their pulley requires the main nut at the eccentric shaft to be undone:

Date: Tue, 08 Feb 2000 16:08:31 -0500
From: Shawn Baumgartner (shawnb@unorthodoxracing.com)

The RX-7 set includes parts like replacement for the entire eccentric pulley (not just the front belt section), losing the weight of that hub is where the gain is, but it also requires extra machine work to make sure the two pieces are perfectly matched.

The accessories are far lighter than their factory counterparts and the water pump pulleys belt section is hard anodized, this is because the back of the belt rides it and would otherwise cut through and uncoated aluminum surface. In addition we use only stainless steel hardware for the 3rd gen eccetric pulley and a stainless steel oil seal for the both the 2nd and 3rd gen eccentric pulleys (2nd gen pulley does not come with any hardware).

The [performance] gains from just the eccentric are posted on our web-site, they were done by Passen. The rest of the set will increase this gain by 20-30%.

In additon we also offer a single belt Ultra R race pulley for the 3rd gens. The full sets only apply to third gens.


Date: Mon, 11 May 1998 12:33:40 -0700
From: Spencer Hutchings

I've had the Pettit underdrive pulley on my car since about a month after I got it. No problems in the last three years relating to the pulley. It is a pain to get belts, but no big deal. And I do have to take it off to get it smogged in CA once every two years.

I think it works as advertised since all the accessories turn much slower with it installed. When I take it off to get the car smogged I can really tell the difference in power and in noise. I don't know how anybody can stand the sound this motor makes with the stock pulley and a free flowing intake. This item uses smaller belts than the stock pulley. I use Goodyear Gatorback belts, very quite, lifetime warranty. It mounts with metric allen head bolts and can be installed in about an hour. It is kind of expensive in my opinion. It comes with the pulley, belts, and bolts, and costs almost $400.00.

Pettit power pulley

Rotary Performance

Rotary Performance makes a kit that replaces all of the pulleys on the car, with the exception of the airpump. They assume you will want to disconnect the airpump, and so do not include the pulley for it.

They may also make a kit that includes that pulley as well, but I didn't pay too much attention to it, since I am taking it off.

Their kits also include the new belts.

They also make their own pulleys, or at least have someone making them for them, so you can get them anodized any standard color.


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