Thread: Unorthodox Racing Crank Pulley Version Info

I had emailed Unorthodox Racing asking for some information on the various version differences between their pulleys for the SR20DE engine. After some checking there, this is what I received back:


The very earliest version of the SR20DE crank pulley, early 1998, weighed a little over 2.25 lbs and had no lightening holes. Each subsequent version of the crank pulley saw minor changes each year to improve weigh reduction. By 2001 crank pulley weight had been dropped down to a little under 1.75 lbs. The pulley continued to improve down to 1.25 lb over the next 6-7 years. In roughly 2008/9 our engineering began to evolve to not only simply reduce weight, as we had done before, but focus on where we reduced weight on the pulley. This focused weight reduction has an even greater effect than the pulleys total weight. Where material is located on the pulley is what determines a pulleys moment of inertia. The moment of intertia determines how much power it will take to re-accelerate the pulley. The more weight we can reduce at the outer diameter of the pulley the better the moment of inertia and the quicker the engine will respond to throttle inputs.

The Rev letters started from N/A which is actually this pulleys second version as we didn't engrave the first version. Each Rev letter was a design and or a weight improvement. Our first part numbering system used 5 digits, this pulley was 1007_ the _ meaning input color # (1= black, 2= silver, 3= red & 4= blue). The second part numbering system was adopted after only a few years and it was 9 digits, this pulley was part# 02100070_ the _ again for colors in the same schema. The Rev letters carried through both systems. Rev H was the last version made on the 9 digit system, it had a large face in front of the first belt (6 rib) with a large UR logo.

When the company moved in 2013 we adopted a system we think is simpler which is comprised of two letters making up the first two spots in the part#. CU stands for Crank Under Drive with this pulley now having part# CU1071, we no longer offer color choices so 1 = Bright machined aluminum and you may see the #1 changed to #3 for hardcoat black on pulleys needing surface protection. This new pulley has no Rev as it is the first version in the new part # system.

The latest crank pulley weighs in at .8 lbs and has a 30% better moment of than REV H which is staggering when you consider Rev H weighs only .45 lbs more than the lastest pulley.

The latest version of the SR20DE crank pulley is only sold in a three piece kit (Part# SU1071A) which includes crank, alternator and water pump pulleys. These new accessory pulleys are also significantly lighter than some older versions we used to make of them. Overall the latest kit improves upon earlier kits by 35% meaning faster throttle response up and down the rev-band.

Please also read more UR pulley facts by clicking the UR.edu link at the bottom of our main page.

awsome tech

Sweet.

I'm clarifying a few points on those part numbers with them. I believe that what they documented to me was the part number in their ordering system, which doesn't exactly match what is on the pulley itself. For example, I've seen pics of a pulley with Part # 1007, and the last digit indicating color wasn't stamped onto the pulley. To me, this makes sense as the color is obvious, and it makes manufacturing easier not having to change the stamp for each color made. Similarly, I have a pulley now that is 0210107, two digits short, one missing digit would have been the color, I'm assuming, and the other missing digit may have been to indicate crank pulley, as opposed to water or PS pump in that same set. Again, the pulley type would have been obvious from looking, so no need to change the stamp for similar parts.

I'll post any additional info I get, and will upload a few pics to this thread also tonight.

Good info...thx for sharing

This just in... Clarification on the part #s:

I've finally remembered to update this thread with some pics.

Borrowing from a thread from canx2k, some pics of a Rev D crank pulley. Weight unknown.






This is one I bought from Mudpuppy, Rev F:





I had weighed this at the post office a while back but apparently erased the note off my phone. It was something like 20oz, give or take. If I go back and weigh it again I'll update this. You can see from the pics that there are two more holes in the pulley for weight savings from the Rev D, visually I can't really tell too much else that's different between these.