I know that underdrive pulleys are supposed to have no ill effects and since it is less rotational weight, it should free up "parasitic drag" but I think there is more to it-I mean what is the point? For Nissan to detune the car by putting on a heavier pulley? Doesn't seem likely.

Besides, I think that a underdrive crank pulley isn't just a pulley, its a harmonic balancer. This piece actually absorbs crankshaft vibration and helps to minimize abuse to the thrust, main, and rod bearings. I know that counter balance shafts are made so that the vibration cannot be felt, but the balancer is for a different purpose all together.

Anyway, I don't see that there would be a disadvantage to changing the water pump and accessory pulleys. I just think that the crank pulley/harmonic balancer is better left alone.

 

Just to respond to the guy who said that since it is an internally balanced engine, therefore the pulley isn't a harmonic balancer is just dead wrong. There are many engines that are "internally balanced", in fact I think all engines produced are "internally balanced." Balancing rotational components (crank, rods, pistons) have a degree of error. I mean not each one of these engines are made from flawless forging processes, hand machined, and balanced to perfection. Don't get me wrong, they are close-but not perfect. That is one reason, another is that it doesn't rob enough hp to make a measurable difference-so what is the reason to do it? I am sure if there was a debate (which there probably are plenty when it comes to this), the accountants would want whatever they can get to lower any chances for need to warranty anything-I would bet that this probably is in the list of engineering specs. Overbuilding and durablitiy in any worse case scenarios concerning slight manufacturing defects. How much do you think that Nissan would spend on, say 100 cars, requiring major labor/parts costs like a problem that could arise from excessive vibration? A relatively low number but call it a measly $2500 (low-low-low) per. What do you think is cheaper, a quarter million or a heavier harmonic balancer?

Anyway, do you think that the extra 3bhp that could come from this is going to put the engine at its peak output? NOT-the engine can be higher tuned for one main reason, it is overengineered anyway. Otherwise it would fall apart when someone tried to squeeze some sauce (NOS as F&F would call it) into it or stapped a supercharger to the intake. Point-The guy who stated that the costing differences between a heavier pulley and a lighter one is negligable is 100% correct. My point is that they don't tune the engine in the 90% capacity rate-that is for the factory built race spec cars (i.e. Ferrari's comp 348TB).

With the quantity that Nissan does in pulleys and pulleys for replacement parts, do you think that they are going to have a slightly higher price thrown at them for a different spec on a lighter pulley? I'm sure Nissan could negiotate a good price on them-would you know the difference if you spent another $30 on a different crank pulley. C'mon....surely a factory having a contract like this would not bat an eye at Nissan-that is if Nissan even outsources it. Think about it, if it were lighter-it may even be cheaper to produce...

What I mean is that is why Mitsubishi did an "internally balancing", a harmonic balancer, and counter rotating balance shafts. Redundancy and every chance to avoid a need for warranty. A harmonic balancer is what absorbs the slightest of vibration and helps to dicipate it or kill it altogether. Its not enough to absorb vibration from a non balanced engine. Do you really think that harmonic balancers are only put on engines that are not balanced? The name doesn't mean that it is the only component that does this-and it really doesn't balance anything, it just kills a possibility in those 4-6% of cars that may suffer from some type of internal vibrations that could cause bearing failure at 40,000 miles. And don't think that you would feel it, between the engine mounts and the rest of the smooth engine, one would likely never tell until failure of one or all bearings that vibration was even occuring. ****, most likely only happens in a very small number to begin with.

Sorry to ramble, just wanted to make sure the correct info was getting posted. I am not meaning to be offensive, I know plenty of people are reading so I just want to represent the most accurate information that I am aware of. If anyone wants to do this, I would highly suggest it AFTER the engine is ripped down, hand balanced by a professional machinist and built for race (taken apart after every few races, inspected, and freshened up with new bearings and honing.) Otherwise, forget about the 3bhp that you might pick up and put it toward getting an exhaust that might bump you to like 15-20bhp.

Hey if you don't believe me, call one of these companies that sell the pulleys and tell them you have a stock 350z and ask them if they will cover the warranty on the engine if something fails and Nissan determines that it was from the subtraction of the heavier stock crank pulley. If they say sure, get it in writing and get your metric wrenches out. Unless you think that the money could be better spent for larger gains