Updated 19 November 2020. We make Rotrex C38R 10 rib pulleys, 10 rib Honda Alternator pulleys (17mm Shaft size), a water pump sleeve and a 10 Rib ATI Damper conversion pulley. This setup enables you to run a 10Rib Rotrex C38R drive. We have made C38R 10 rib pulleys in 71,75,80,85 and 90mm and are usually in stock. Other sizes can be made by special order.

My boost comparison projection of a C38R upgraded from the C38-91 turns out to be pretty close. See below.

The 10 rib drive is also an excellent solution for spinning a TVS2300 to it's maximum boost.

10 Rib Honda K20/K24 10Rib Rotrex C38R drive. The ATI damper pulley goes from 37.5mm to 41mm wide. Our 10 Rib Alternator pulley becomes 43.2mm wide.

The water pump sleeve adds 4.7mm to the stock width pulley.

The part number for the ATI DAMPER is 918477, and our outer 10 rib ATI hub pulley retains the same drive diameter as ATI at 5.5"/ 139.7mm.

The C38R drive ratio is 1:6 with a maximum speed of 90,000rpm impellor or 15,000rpm input shaft speed.

Pulley size calculation example.....If your motor revs to 9000rpm then the C38R pulley needed is 9000*139.7/15000 = 84mm so use a 85mm pulley.

For the water pump 10 rib pulley I have made a batch of sleeves. The inside sometimes needs to be machined as they can vary from Honda.
My stock Honda water pump pulleys here vary between 123.9mm to 128.04mm outside diameter.
We need 0.3mm to 0.5mm clearance to slip onto the water pump pulley. (assuming that your pulley is not damaged). At the 0.3mm clearance it's quite tricky to fit as it must be perfectly aligned to slide on. I was fiddling on the bench for a while and sometimes it just dropped straight on, sometimes needed a rubber hammer when it jammed 1/2 way or was as I was out of true.

I have worked out 2 set's of prices. $159 Australian + post for a 124.17mm inside plated sleeve or $229 Australian plus post when it's a custom machined to the customers water pump pulley size + 0.3mm.

If you want me to machine one to fit measure your water pump pulley outside diameter in x3 different places and give me the largest OD mm.

They slip on with 3 bolts to hold them in position and add 4.7mm to the width of the stock pulley. Use my pulley as a template drill through into the stock pulley and fit 3 off 5mm bolts with nyloc nuts.

Why use a C38R? Here is a comparison between the C38-91 and the C38R. The C38R has approximately +30% more flow so needs +30% more belt to drive it.

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Jeff during business hours. 0420 355 307

email: jeff.david@quantumGP700.com.au

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