We've had lots of questions about crank pulleys lately, so here's all we know.

First, the crank pulley is the main pulley on the end of the crank (duh) that drives the accessories -- alternator, water pump, and air conditioning compressor.

An "underdrive" crank pulley is a pulley with a smaller diameter. The result is that it drives the accessories more slowly, and with greater mechanical leverage. It's like pedaling a bicycle up a hill with the smallest sprocket engaged on the crank. The goal of the underdrive pulley is to reduce drag from the accessories on the motor. Of course, if the accessories are turning more slowly, they will also be that much less effective, but life is all about compromises.

Does an underdrive pulley really add horsepower? The pulley manufacturers say they do, and we've seen tests in magazines that seemed to indicate signficant gains. But you could get the same sort of gains during a drag race WITHOUT an underdrive pulley by removing the belt from your alternator. (The motor can run solely off the battery for a short time.)

The other benefit of aftermarket pulleys is to reduce rotating mass. Here the simple aluminum crank pulley has a big advantage over the heavy stock pulley, but there's a reason it's so much lighter: It's missing the harmonic dampener. The reduction in rotating mass may be worth a couple of horsepower. But removing the dampener seems like a bad idea to us.

The factory crank pulley has a built-in harmonic dampener, in the form of a split design, with a thick rubber pad sandwiched between two steel sheels. The dampener is designed to absorb torsional and vertical vibrations from the crank. MOST underdrive crank pulleys (with the exception of the Buschur Racing model) do not have a harmonic dampener at all.

Torsional vibration is a twisting vibration caused by the pulses of each combustion event. The force of the piston causes the crank to deflect ever so slightly in the direction of the force, and when that force goes away the crank ever-so-slightly springs back. At certain frequencies the crank can resonate, making the vibration much worse. This is where the harmonic dampener comes into play.

Although many DSM owners have removed the harmonic dampener crank pulley without incident, doing so almost certainly increases crank bearing wear, and COULD lead to early failure of the crank or crank bearings. Just how much the life of these parts is shortened is unknown.

We do have one piece of first-hand experience, to offer, though. We know of ONE instance of crank failure on the 4G63 motor. It was a 2.3-liter motor that belong to an employee of ours. The crank cracked in two -- the only time we have ever seen this happen. That block had an undampened crank pulley on it.

On a race motor, increased risk of bearing or crank problems is insignficant next to the risk of, say, detonation in the cylinder that could blow up the motor. So for a race block, we heartily endorse lightweight undampened crank pulleys.

But for a street-driven car, one that you might want to last a couple of hundred thousand miles, we do not recommend using a pulley without a harmonic dampener.

One last note: The rubber in the OEM crank pulley gets old and weak over time, and it's not uncommon on high-mileage motors to see the crank pulley completely come apart. This can be a serious problem if the accessory belts wind their way into the timing belt area. The moral of the story: Inspect your crank pulley the next time you're working on the car, and replace it if it shows any signs of looseness or wobbling.

I personally know five people that have ruined their main bearings after about 15K miles of non- OEM pulley use. Main bearings on Hondas don't normally fail; it's usually something else. Two main causes of bearing failure are lack of oil and excessive vibration. Since the bearings didn't spin, lack of oil can be ruled out, and since all five cars had underdrive pulleys, and all five failed right around 15K miles after the install of the pulley, through process of elimination, I've decided that the underdrive pulleys were at fault.

I live in vegas, where it gets hot, I installed it myself, just the crank pulley and it was a pita!!!
immediately I noticed major a/c cooling loss...to much underdriving for me. performance wise, well it does pick up quicker, mid-high end power has improved, over all I don't think it was worth the price and trouble installing it. Considering sticking my stock pulley back on. This underdriving of 15% is not true, its more like 50% They state the performance is from weight reduction, then why not offer them the same size as stock made out of aluminum???
All in all, its a racing pulley, if your racing get it, if not don't waste your time under driving everything...
my .02

If you look carefully at a Honda "pulley", you'll find that it's not a single piece of metal. Typically, there's a nodular iron or steel hub and another "ring" of iron or steel surrounding it containing the belt grooves. The two parts are joined by a rubber layer, which is highly compressed and sandwiched between them. Why rubber? If you notice, many four cylinder engines over the years have used counter rotating shafts to help make the engine "feel" smoother. Reciprocating internal combustion engines and especially in-line four cylinder versions, all produce shock pulses, which are very apparent to the occupants of the car. Every engine produces a shock pulse each time an individual cylinder fires. So, in the case of the four cylinder variety, there are four large individual pulses for each 720 degrees of crank rotation. Each time there's a pulse, it causes the internal components to do a rapid acceleration-deceleration event. When you consider the mass of all the internal components and visualize all these parts stopping and starting during their reciprocating and rotating motions, the additional stress "spikes" tend to make it all the more reason for one to wonder how any of it can work for any length of time. The harmonic balancer is made with the rubber coupling so that, when the individual "spikes" occur, the inner portion may move with the crank, but the rubber connected outer ring's mass helps prevent the hub and crank from going as far or as fast during the spikes or pulses. Remember that the outer part had considerable mass, so it tends to want to stay in motion at the speed that it's traveling and that's why it can prevent excessive harsh motion by the crank and other internal parts. To put it simply, the harmonic balancer is a shock absorber for the engine and thus prevents the individual pulses from destroying everything in the engine.

Make sure whatever pulley's you decide to use that they have some type of dampener.
Without a dampener the pulley may create excessive vibration in the crank causing damage to internals or oil pump failure.
This may happen even as a result of a lightweight pullet regardless of dampening.

I ran a lightweight OEM Civic Type R crank pulley on my Integra GSR block. (The GSR crank pulley is huge, and has slots for PS, AC, Alternator compared to the CTR Crank Pulley with just a slot for the alternator).
Even though the CTR Crank pulley is dampened, I still managed to shatter 2 oil pump gears!(which lead to spun bearings & blown turbo! ) I had no clue why. When I changed back to the stock GSR Crank Pulley, I never had the problem again.

I also do not believe that the weight of this pulley is really what provides the majority of the WHP increase, but the fact that it is actually under driving the accessories by 25%. I think a heavier pulley of the same diameter would show similar results on the dyno. My rough calculations for a 4 lb 6" disk to spin from 3K to 7K in 5 seconds, takes less than 1HP, so most of the gains are obviously not coming from the pulley weight reduction.

Originally posted by ponyman
Umm.....Thanks, but could you summarize...I don't really want to read all of that...

Originally posted by C2i0v0i1C
note to self, if ur to lazy to read important ****, dont buy stuff for ur car

Originally posted by Ershall
You won't hear anything from Josh in any forum it seems. PM him or email him. Derek said he will most likely be banned sometime soon...I have heard enough from Josh to learn that he is full of ****...but if you want to hear more, PM or email him.