Neutered Sputniks

As long as the outside diameter remains the same, it shouldn't affect water pump, A/C, alternator performance.

Just keep in mind that there's no performance benefit. So if you're looking to see a performance increase - spend the money elsewhere. If you just want the bling, go for it.

ap1_tot

^^ Interesting point sir sputnik. Worse case scenario would be not only wouldnt it yield gains, but it would mess up other components of the car as well.

So basically, what you're saying is that those who complained of having problems wit the alternator, etc can have the wrong diameter pulley to blame, and not on being lightweight?

Gernby

What kind of pros / cons are you looking for? From a performance standpoint, these pulleys are going to be about as effective as a wash and wax. There may be some theoretical improvements in performance, but mainly it's just going to look better, and make you feel better about the car.

ace123

I'd go with a lighter flywheel. Glad you like it though.

Neutered Sputniks

I wouldn't expect any kind of performance decrease on other parts.

What your friends with problems probably installed are/were underdrive pulleys. Basically, they're a different size of pulleys - the theory being that if the alternator spins at 9000rpm stock (it doesn't, btw), by putting a different size pulley on the alternator, you can decrease it's revolutions. Each revolution decreased, theoretically, reduces the energy used to spin that pulley.

This doesn't work so well with the alternator because it's main resistance to spinning is caused by the electrical field generated inside. Even if you spin it fewer times, your power drain is just as high and thus your alternator will work harder to make up for the fewer rpms (again, a net negligible difference in power).

The theory behind the smaller (in ratio) pulley for the water pump is essentially the same - fewer revolutions means less parasitic drag. However, fewer revolutions also means the pump isn't pumping as much coolant - and I wouldn't be surprised to see overheating issues on an engine with such a setup.

I would expect the A/C performance to be hampered as well (fewer revolutions of the compressor pulley, doesn't work as well as stock). Rather than put an underdrive pulley on the A/C, just go buy the A/C removal belt. Shouldn't be more than $20 for a high quality belt. That's one investment that could actually yield some returns (less parasitic drag due to eliminating the pulley all-together).

Gernby

I haven't done any testing to see if this is an issue on the S2000, but it's possible that underdriving the water pump could actually increase coolant flow at high RPM's due to reduced cavitation. Peak flow of the water pump might occur at RPMs significantly lower than red line, then beyond that, flow might drop off. I'd really be interested in trying some different sized water pump pulleys ...

Neutered Sputniks

Good point.

That's also going to depend on the age of your water pump - i.e. as the impeller wears, the max cavitation RPM will shift.

I'd like to think the Honda engineers knew what they were doing when they selected the stock pulley diameters. I really doubt you'd see much of a flow improvement by moving to a different diameter pulley, whereas I could easily see a decrease in flow.

Gernby

I have no doubt Honda engineers did know what they were doing. However, their impellar choice and water pump pulley sizing was probably biased toward stop and go driving moreso than road racing. I suspect that if they had chosen an impellar and pulley that would be optimum for 8K RPMs, then it might overheat at idle.

Neutered Sputniks

I had that thought as well. Good luck in your endeavor

maluch

not to mention the fact that the stock pulley has a drilled hole that makes it rotationally balanced with the engine internals while the aftermarket do not...

the counter argument often given to the statement above is that lightened flywheels are not blamed for rotational imbalance. the difference with flywheels is that they are connected to the rest of the rotating drive train all the way up to the wheels. this adds mass, increases rotational inertia, and rotational momentum to that end and makes it very stable and a great dampener of of vibration

regarding the 40% drop in mass. the power gain will be proportional to the (very large)rotating inertia of the of the rest of the system...

the reason you found a marginal difference in response is because you had the clutch engaged thus constraining the inertia of the system to include only the engine internals and the flywheel. If you would repeat the same experiment while measuring straight line acceleration you would find a much smaller difference, probably not even measurable.

take it from an engineer, these pulleys are for race cars that are rebuilt every two, or less seasons and will reduce the longevity of the engine...