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I've been afraid of U/D pulleys, but after looking at many KL dyno sheets, I'm considering them. So.... If you have, or had one please answer the poll!
If you HAVE had a problem, which brand was it, and what was the problem??
I allowed 2 answers, in case you had a bad one, and a good one.
Thanks!

Poll for some reason not accepting my vote of "no".
No problems over 100K miles with Unorthodox lightened underdrive pulley installed on Nissan vq35de. I have no dyno proof of increased hp or tq, but the UD pulley did seem to increase throttle response. Most people worry that the solid aluminum pulley is not providing the proper harmonic balancing versus stock pulley, but that is nonsense for any internally balanced crankshaft. A lightened pulley provides similar benefit as a lightened flywheel. Both pulley and flywheel must be independently balanced (think balancing a wheel) but in most cases are not necessary to balance the crankshaft.

Best info I have seen is at this link . In the FAQ on unorthodox racing they say essentially the same thing.

Thanks. That's alot of miles! Good testimony. I've seen them work on other cars, too, but for some reason they have come apart on about 8 KLs that I can think of. I'm leaning toward doing it....
I don't know why the poll won't work

Which 8 KL's had problems with it? And what exactly fell apart, the pulley or the engine?

We installed one on our ice racing car and took it to the track for one full day of race, nothing negative to report on that short period of test. Was also not to hard to fit. Mine was bought used and came with both strap. Only down side so far is that your reference mark for timming is further then OEM, so checking timming is little less obvious

Haven't heard much positive. Of course I don't run one. I guess it's more for a track car rather than dependable daily driver. I think even my Cobra still running on stock one and it's HIGHLY modified. For what hp/tq it frees up I don't think it's worth it on daily driver anyways.

Oh my god! KL engines' crankshafts are internally balanced! This answers all my questions. I was wondering before if these were safe or not but with this new info it sounds like there should be no problems!

Of course mine has one and I've read some negative stuff about them. I'll wait and see but so far no probs reported regarding mine.

I tried it, and I really wanted it to work. I got a cheap ebay OBX and it didnt work. it caused my car to sound funky. You know how you can "feel" your engine... and well I didnt get much power freed from it. If you are looking to free up some power, go to manual steering rack. The underdrive pulley causes your alternator to not spin enough at low rpms, my lights would dim .. I guess because it was obx and the crank sensor blades may have not been aligned. I was not satisfied... also I left a scar on the oil pump assembly as I had to shave some of it to let the pulley fit.

I don't remember which engines had trouble, as it was over the past 5 or 6 years. It seems like the ones that failed were the Ebay ones. The problems, as I remember are; The sensor blades part would seperate from the main pulley part, it does spin everything slower, but I have a very good alternator, and my headlights use less energy than OEM. I'm also thinking about getting an electric water pump.
I'm thinking about the manual steering swap, but want to drive an MX-3 with it aggressively, to see if it's good for autocross.
I'm glad you figured it out, NightShade. My rotating assembly was balanced beyaond OEM specs.

Thanks, Dan, and Ice Racing. I have MegaSquirt, so timing is no problem.

People always like suggesting the manual rack for more power, but it seems that most are only interested in going fast in a straight line...keep the PS for autocross forsure.

Ya, the issue with an UD pulley isn't about running a UD pulley and affecting the motor in a negative manner, but a failure of the UD pulley itself form the cheaper units out there, as you just described.