There are many reasons why the OEM decides to go with certain things that would seem "restrictive" to the tuner market. Why does Nissan put restrictions in the intake/exhaust system to make the car more quiet rather than more powerful? Why does Nissan make the clutch, flywheel, and pulley system heavier to change drivability patterns when lighter would yield higher hp & tq numbers? There are many reasons. One main reason is that while these are sports cars, the majority of them are sold to older people who have expendable income, want a fun but very "driveable" (quiet, calm, subdued, fuel efficient, smog friendly) car. These owners are going to buy these cars and leave them unchanged. To the OEM, their money (and needs) talks louder than the younger tuner market, regardless of how much we tuners think we love our cars and our knowledge regarding performance and cars in general.
Regarding the weight of the pulley... lighter is not ALWAYS better and there is a fine line that can be crossed. We believe that our lightweight underdrive crank pulley is in the correct range... not too heavy, not too light. Going TOO light would disrupt the natural balance and would lead to driveability issues.
In relation to using a stock diameter lightweight crank pulley vs an underdrive crank pulley... weight reduction generally leads to better throttle response, quicker acceleration, and a slight increase in fuel efficiency. An underdrive lightweight crank pulley, such as the NST piece, goes one step further to release a few extra hp and tq which can be sent to the wheels instead of the accessories.
A properly designed UNDERDRIVE lightweight crank pulley will always beat out a stock sized lightweight pulley if put side by side on a dyno or race track.
The only time a stock diameter lightweight crank pulley would have an advantage would be on a supercharged car. SC systems generally run off the crank pulley and would see less boost if an underdrive crank pulley was used.
There is a good amount of info in the new thread I recently started, regarding the NST Underdrive Crank Pulley Kit...
NST (NonStopTuning) 370Z VQ37HR Pulley Kit Review w/ Dyno Charts
Please feel free to contact us by phone or look for us on AIM should you have any further questions or want to discuss these questions in more depth. I'd be happy to chat with you.
