This argument is a huge one over at twinturbo.net. Many, many people fight about this about once a week. There are claims that yes, the pulley is a harmonic damperner and should not be removed and some say that it wont matter that much. There are people on there that have had them on for 75,000 to 100,000 miles on their Z, either Turbo or not that still have properally balanced engines. Again, there are a few that claim the pulley damaged their engine by messing up the balance.

The point to all of this is any modification is going to increase the likelihood of having a problem with your car, you just have to judge whether or not the modification is going to make up in power. Personally, on my Z32 NA, I have an intake, pulley and exhaust, and the pulley is what made the power out of all of those the most. Much better throttle response and power throughout the rev range.

 

I di crank under alt over on my FireHawk and got .2 increase in the 1/4.

I will not do it again though because what I also got was too low of an idle which resulted in numerous stalls in reverse when the idle was low and my foot was off the gas.

I also heard horror stories of the bolt loosening that holds the Harmonic Balancer in. This was on a LS1 350 engine with numerous mods including a high stall TC (A4)

 

I think that is the gist of the debate. Yes, you probably are taking a small risk, but you do with most mods.

 

I have had an underdrive pulley on my present car for over 60K miles and have had no problems at all. In fact after installing it, the performance gains were dramatic and immediatley noticible on a small 2.5L v6. Further, the difference in weight when holding the two pulleys in hand were truly astounding- stock was extremely heavy. I would install one again if given the chance. Just my .02
Rizz

 

underdrive pulleys are a larger diameter not smaller, a smaller diameter will only spin the accessory faster creating more drag

 

My underdrive pulley for my 300ZX is definitely smaller and weighs about 8-9 lbs less. (Stock is about 12lbs). All underdrive pulleys are smaller than their original stockers.

 

depends what pulley you are replacing if its the drive pulley smaller is better, but some vehicles its the driven pulley that you replace and believe me it will not be smaller, maybe lighter but not smaller, smaller on the driven pulley will only put more strain on the engine, and some vehicles its the driven pulleys that get replaced, like if you want to up the boost on a SC you put on a smaller pulley on the blower or a larger pully on the crank.

 

An underdrive pulley is typically the crank pulley and it is most definetly smaller and lighter

 

not all applications are the crank pulley, some setups allow you to underdrive some accesory while leaving others un-touched, on my Big bloch chevy i could buy individual pulleys such as alternator and waterpump, they wer definitely lighter but also larger to reduce overall speed

 

this is true, but when most people say " an undedrive pulley" they refer to the ones that replace the crank........anywho........back to the topic at hand