The Raceonly Billet Water Pump Pulley had an almost identical 104mm diameter as the old 103mm Greddy water pump pulley that was previously installed on our engine. This is a 24% reduction in speed over the factory 85mm water pump. Note the deep grooves in the Raceonly pulley that increase bite on the accessory belt to reduce slippage on the water pump. These grooves are far more aggressive than the no-name brand pulley (right).
The stock water pump has a 1.29 pulley ratio while the Raceonly has a 1.06 pulley ratio. At the RX-7’s stock 750rpm idle, our water pump will be slowed down from 971rpm to 793rpm. This is not significant, but where it really makes a difference is preventing cavitation at high engine speeds by lowering the water pump’s RPM from 10,353rpm to 8,642rpm at the RX-7’s stock 8,000 engine rpm redline. At 10,000rpm at the engine, the stock water pump would be spinning at 12,941rpm; with this larger Raceonly pulley, it will now be spinning at 10,577rpm which is almost the same as the water pump spins at the stock redline.
The Raceonly Billet Alternator pulley measures out at 65mm. This is much larger than the stock 50mm alternator pulley and changes the pulley ratio from 2.2 to 1.69 which is 23% slower.
At the RX-7’s stock 750rpm idle, the stock alternator with a 2.2 pulley ratio would therefore be spinning at 1,650rpm. With the new, larger Raceonly pulley with a 1.69 pulley ratio, at the stock 750rpm engine idle, the alternator is now spinning at 1,268rpm.
The DC Power 180 amp HP High Output Alternator turns off and no longer charges at 1,200 alternator rpm. If we were using this 65mm pulley setup on a stock engine, we would be at the borderline of the alternator not charging. Since our engine is bridge ported and semi peripheral ported, we are targeting a 900-1,000 engine rpm idle, which will put us at 1,521 to 1,690 alternator RPM. For our application, we will have plenty of headroom and amperage at idle and at our maximum target of 10,000 engine rpm, the alternator will be at 16,900rpm, which is well within the 20,000rpm internal rating and is actually slower than the rpm the stock alternator spins at the factory 8,000rpm engine redline.
In Part-9 we installed the Full Function Engineering Idler Pulley when we removed the air pump.
The FFE Idler Pulley is very well-made and worked great prior to our engine build. It looks fantastic in our engine bay and increases the contact area of the serpentine belt on the water pump pulley.
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.