Unorthodox Racing Underdrive Pulley

[5/23/2000] Reviewed by ELi Peraza -

Applicable to '90 - '97 1.6 liter

I bought a crank pulley from Unorthodox racing plus a water pump pulley and an alternator pulley from Racing Beat. THe finish and quality is super for all of the items. The crank pulley comes in an anodidized blue color so I matched the water pump pulley and the alternator pulley with the same color. I spend 170 dollars for the crank pulley, 60 dollards for the water pump pulley, and 38 dollars for the alternator pulley. I also installed a 160 degree thermostat from finish line performance to avoid overheating in the future.

Installation is not for the unexperienced. A local shop might charge you about 300.00 dollars for this job. I decided to do it myself to learn more abou my roadster. It took me about 5-7 hours to do this job. Luckily my uncle owns a shop so decided to be a mechanic for one day. I tell you it is very difficult job. You have to unbolt the intake, the radiator, the sway bars, plus the plastic cover underneath the car. Luckily I took down the plastic under the car a long time ago so my job was a lot easier. At the end of the day, and with the advise of a mechanic, I was able to figure out how to install the crank pulley (you need and air gun) but after that, installation was a lot of fun.

Performance wise I can only feel a slight difference between 3000 to 5000 rpms. I know that if I have an RX-7 Air flow meter this condition might change. I also feel a lot of restriction from the mufler. The car seems to be to restrictive with the stock exhaust. I will update my exhaust with an HKS super dragger in the future. And of course a high flow catalytic at the same time. My power steering is a lot better. But again I am not sure whether this is the best addition I have done to my car. I also installed a Voltmeter and an Air-Fuel gauge from Autometer. I did this to monitor the alternator and to adjust my car in the future. That's it for now. Thanks, Eli Peraza

Over 30 minutes to remove completely

Reviewed by: Anonymous

Unorthodox Racing Underdrive Pulley part #08021 'Ultra-Street' for 1996 Miata M-Edition with A/C+P/S and ALT+W/P belts.

Installation instructions are included but, are so simplistic as to be of little use; eg., "remove belt(s), remove old crankshaft pulley, install new pulley, replace belts". If you have serviced your Miata timing belts before, this job will seem simple. If you have replaced your ALT+W/P or A/C+P/S belts before, this job will be familiar. Else, the shadetree mechanic should understand how to properly adjust the tension of both belts, have solid stands or ramps to work underneath, and be prepared to deal with tight fasteners located in awkward places.

Not included with the "undersized" pulley are the undersized belts or, the four fasteners required to install the (smaller diameter but thicker) new pulley. At the time of purchase, information posted on the Unorthodox Racing website regarding proper belt sizes was incorrect; and there was no mention of fastener replacements whatsoever:

ALT+W/P belt, MAZDA P/N: B6BF-18-381 standard;
undersized replacement was GATES P/N: K040340 Micro-V.

A/C+P/S belt, MAZDA P/N: BPE8-15-909 standard;
undersized replacement was GATES P/N: K040355 Micro-V.

standard Miata (4) crank pulley fixing bolts: 6mm x 16mm; 1.00 pitch

replacement (4 required) pulley fixing bolts:

6mm x 20mm; 1.00 pitch (what we used)
6mm x 25mm; 1.00 pitch (probable longest usable)

On our 1.8L '96 M-Edition, there was a steel plate fitted behind the pulley, as well as a large steel washer used in front of the pulley, just behind the four pulley fixing bolts. These pieces were not shown or referred to in the instructions - we cleaned these parts and re-used them when installing the new underdrive pulley.

The first test drives were without incident however, a few days after installation, some squealing was evident upon engine startup (belt slipping, perhaps some stretching) so, we increased belt tensions and everything has run perfectly since.

This is a high-quality, CNC-machined and anodized alloy product from a supplier who does not specialize in Miata-specific applications, offering only modest support.

If you are intending to replace your old, worn belts, replacing the OEM steel pulley with this undersized alloy pulley at the same time is only a bit more effort.

Note that, if you are thinking about bolting on a (belt-driven) supercharger someday, you do not want to install an undersize crank pulley.

The undersized crank pulley reduces engine drag from the ALT+W/P and A/C+P/S accessories. The power gain is modest, but is apparent throughout the torque curve when measured - to the driver, it feels somewhat like a "lightened flywheel effect" (though not so pronounced as an alloy flywheel would be).

And it is a beautiful piece of functional alloy on the engine. The only issue with this modification appears to be ALT charging and W/P cooling efficiencies - we have experienced no degradation of electrical or cooling performance whatsoever with the Underdrive Pulley on our '96 M-Edition.

Reviewed by: Jeff Alton -

This is a smaller crankshaft pulley designed to reduce the speed at which your water pump, power steering pump, alt, ac turn at.

The product installed in about thirty minutes. However it requires 4 new bolts, as the oe ones are too short. You will also have to purchade new belts that are 1 or 2 sizes smaller tham the original ones.

The shop that sold it to me claims that they dynoed this mod on their dynojet and bot an honest 5 hp at the wheels. I can't say if this is true or not, but there was a noticeable improvement in throttle response.

Under 30 minutes to remove completely

Reviewed by: Rick Carter -

Underdrive pulley to replace stock alternator pulley on the lower part of the engine (Available for 1.8/1.6 engines).

I had heard of underdrive pulleys for a long time (from the days of yore when musclecars ruled the earth), but have had a hell of a time finding one for the 1.8 engine. Then I got online and found a place that had them. Only for about $140.00 also. You can get it in different anodized colors (mine is blue to match other blue goodies in the engine). Easy install if you are partially mechanically inclined. The principle of the pulley is to reduce loss to the working parts of the engine like the alternator, power steering, and a.c. The pulley doesn't let the accessories use as much power. Can be up to a 10% increase on highly tuned engines!!!!

You MUST use smaller belts for the compressor and alternator. My '94 sport model with a.c. and no power steering requires both belts to be stepped down one size, two will also work because of the adjustability of the tension on the belts. Have to remove the intake to get to the old pulley, but they send good instructions, and have a tech line. WORTH IT BIG TIME. Trust me, you want this product. But don't run the a.c., stereo real loud, lights, and windshieldwiper on full blast too often, you won't have as much alternator power available, but who cares for the power difference in the engine!!

Under 30 minutes to remove completely

Back to Product Reviews 15 December, 2001