I read something from a forum about harmonic balance. It has something to do with vibrations i think and that the regular pulley was made in part to balance? is this true, and if so, does it affect maximas as well (i read that the wrx do not have to worry about this)?

 

I just had my UDP installed, the harmonic balance in most engine nowadays are inside the engine, it is not part of the pulley(check the FAQ on Unorthdox racing website), the rubber ring you see on the OEM crank pulley is just a "noise/vibration reducing unit" it is not the harmonic balancer.

This myth came from the fact the old American V8 has the harmonic balancer outside the engine block and when people installed pulley it was removed and caused the problem(blown engine). But most modern engine now have this device inside the engine. If you look at the Gen4 maxima it does not have the rubber ring on it hence it is not the device people think it is.

Just make sure when the UDP is install do not pry out the oil seal(or if you want you can put in a new one), once that is taken out you will see all your engine oil dripping to the ground~

I have been running the UDP for 3 weeks, and it is very smooth(better than stock), which certainly not a sign of lacking the harmonic balancer. My Nissan mechnics (20yrs experience) looked at it and say everything looks ok....Also the quality of the UDP matters as well, for Unorthdox I don't think its an issue....

 

Here's a great review and answered a lot of my questions:
http://www.greghome.com/Greg's%20Garage/1999%20Nissan%20Maxima%20SE/Underdrive%20pulley.htm
I'll probably be getting one pretty soon.