We upgrade the electrical system of our car with a high output alternator from DC Power, improved the look of our engine bay with a set of Raceonly Pulleys, and ensured accurate engine timing at high RPM with the Full Function Engineering Hall Crank Trigger Kit.
The factory 100 Amp alternator on the FD RX-7 was built by Mitsubishi Alternator Co. and was barely sized for the maximum electrical demands of a stock RX-7 with little to no headroom for greater demands. A stock car with a functioning new alternator should output 14.1V to 14.7V at idle.
However, alternator output is greatly reduced with heat and age, and the stock alternator has been proven to be insufficient in extreme conditions like hot summers in Arizona or when being pushed on a racetrack; even on a stock car!
If an FD RX-7 has a modified stereo or makes more power than stock, it quickly becomes apparent that the stock alternator is insufficient and a major limiting factor. It is common for FD RX-7’s to see voltages of 13.3V to 13.7V while experiencing many electrical-related issues such as difficulties starting the engine, poor idle, and inconsistent engine performance.
To solve this problem, we turned to the electrical experts at DC Power who offer a 180 Amp HP high-output alternator for the FD RX-7. This alternator outputs an incredible 14.8V and 100 Amps at idle! That is the same output that the factory alternator makes at its peak.
DC Power Engineering designs and manufactures 100% new alternators that are Made in the USA or OEM sourced with the best components and latest technology. They are constantly innovating and offering new products to the community and are heavily involved in racing, off-roading, street cars, RVs, and competition audio systems. They design their alternators to survive the harshest conditions and demands and have a great reputation for the performance and quality of their alternators.
DC Power is awesome to work with. If you have a custom setup or a unique electrical challenge that is not ‘off-the-shelf’, they will help tailor a custom alternator setup to your needs and the demands of your application and will do the math and recommend pulley sizes based on the rest of your setup to avoid over or under-spinning the alternator. An alternator for competition audio events in a domestic V8 is significantly different than one in a high rpm 4-cylinder race car. With their vast experience and great customer service, DC Power are an amazing resource to ensure your alternator setup works flawlessly.
PULLEY SIZING, RATIOS, AND “UNDERDRIVE” PULLEYS
When it comes to slowing down the speed of accessories like the alternator, water pump, or power steering pump, this can be accomplished with smaller diameter “underdrive” crank pulleys or larger diameter pullies on the accessory itself.
To determine the pulley ratio, divide the crank pulley diameter by the accessory pulley diameter. If the crank pulley is 110mm and the alternator is 50mm; this gives us a 2.2 pulley ratio. If we multiply the pulley ratio by the engine rpm, that will give us the rpm of the accessory.
As we started mounting the accessories on our long block, which we assembled in Part 19, we went down the rabbit-hole of pulleys. We bought these blue underdrive pulleys from Banzai racing to match the color of our engine block. Unfortunately, Banzai does not market or disclose the crank pulley size, so we measured it for ourselves:
Crank (aka: main, E-shaft) Pulley
- Stock: 110mm
- Banzai Racing ‘underdrive’ Pulley: 97mm (11.8% reduction in speed of accessories).
Power Steering Pulley
- Stock: 115mm
- Banzai Racing: 115mm
Alternator Pulley
- Stock & Banzai Racing: 50mm
Water Pump Pulley
- Banzai Racing: 85mm
Idler Pulley
- Stock: 85mm
A/C Compressor
- Stock: 126mm
The stock crank pulley measures 110mm while the Banzai underdrive pulley was 97mm. This is a 12% reduction in speed of the alternator, water pump, A/C compressor, and power steering pump.
8 comments
Looks so good! This article told me that my alternator on my Subaru EJ is kind of tired. pushing out high 13s voltage only.
Billy, this build is going to be epic. We all can’t wait to see it on track!
I’m surprised no special crank damper like an ATI or Fluidamper, any particular reason why?
Rotaries don’t require dampers.
Correct, they do not.
The “no name” brand pulley is GReddy. One of the first under drive pulley sets to come out for the FD in the late 90s.
Thank you 🙂
Does the trigger wheel work with the Apexi power fc ecu? Been a while since I’ve worked on the car and have forgotten more than half when I was knee deep into the FD 10+ years ago.