Unorthodox Racing pulleys

I have been talking with a friend about the UR pulleys. He said the the UR crank pulley is not as smart as a stock pulley, due the fact the most stock crank pulleys have some sort of vibration dampening engineers into them, while the UR pulley does not have this dampening built in. He has heard of these pulleys breaking under stress. Just wondering what everyone's opinion on the matter is here. Should I go for all the pulleys, or all execpt the crank pulley?

i haven't heard of them breaking due to stress. maybe on american (ford, chevy) motors, but the sr20de is internally balanced, so the crank pulley won't be doing any of that work. there wouldn't really be much point in changing all but the crank pulley, since that is the one that makes the biggest difference. also, i have been doing some diggin around on the pulleys, and most articles i have read say not to bother with the four pulley set. just go for the two and spend the extra cash on something else. the second two pulleys make only about one extra pony. not worth it to me.

maybe we can get a group buy going here, eh?

Here's the data i found...

SE-R Pulleys
( data from http://www.geocities.com/n_dahi/ )
Stock UR % diff Savings
Crank 78.00 oz 19.30 oz 75% 58.70 oz
Power Steering 16.30 oz 4.30 oz 74% 12.00 oz
Water Pump 9.40 oz 6.60 oz 30% 2.80 oz
Alternator 9.40 oz 4.30 oz 54% 5.10 oz
Total 113.10 oz 34.50 oz 69% 78.60 oz

Forget oz's, you should be looking at hz's, as in Hertz (not the rental company, but the frequency). What manufactors are trying to do with balance shafts, harmonic balances, etc... is to prevent the existence of first second and third harmonics in the Engine. Harmonics may be good for a musical instrument, but not in an engine, where the harmonic frequencies build on themselves, vibrating things to death. Adding Mass to assemblies changes the natural frequency of the assembly. That is one way to tune out harmonic resonance.

I would say that there is some safety margins allowed when engines are designed, so a small change in mass wont affect things too much.
Personally, I wouldn't change the crank pulley: the benefits of the mass savings and size difference isn't large enough for me to justify possible engine damage. Although I guess that Lightened Flywheels could be seen as doing the same thing as these pulleys...

Originally posted by qab5b
Harmonics may be good for a musical instrument, but not in an engine, where the harmonic frequencies build on themselves, vibrating things to death.
<snip>
Personally, I wouldn't change the crank pulley: the benefits of the mass savings and size difference isn't large enough for me to justify possible engine damage.

You are correct about the harmonics, but only to a degree. Mike Kojima calculates that the the danger is quite minimal with the SR20.

I remember reading the specifics, and they are in the SE-R Mailing List archives, but I don't remember them off the top of my head.

Originally posted by P10DET


You are correct about the harmonics, but only to a degree. Mike Kojima calculates that the the danger is quite minimal with the SR20.

I remember reading the specifics, and they are in the SE-R Mailing List archives, but I don't remember them off the top of my head.

I found Mike's write up on se-r.net.
http://www.se-r.net/car_info/engine_performance_tuning.html#Unorthodox%20Racing %20Underdrive%20Pulleys

Looks like these things are OK. I guess it is a use at your own risk part. Results will vary. I am guessing also that these pulley's might not cause problems, but might amplify current problems.

I would stick w/ the 2pc set.

There's going to be a group buy on the B15Sentra.net forum. Look in the Classifieds.

The link is also in the SR20deforum.com