SILVER SURFER

This link goes into great detail regarding an under drive pulley for the WRX, chek it out; http://www.uniqueautosports.com/pulley_kits%20300ZX.htm

Based on my experience with Under drive pulleys, I have no doubt that they free up TQ/HP allowing you to put more power to the ground, 10-15WHP sounds reasonable to me. I like it because it frees up torque every where, not just at certain RPM points, so the real world acceleration gains end up even better than what the peak HP increase would indicate.
There are of course some potential concerns with this mod, and that is the feedback I am really looking for. Some of these concerns are disscussed in this link although I have no way of knowing if there conclusions regarding harmonic resonance issues are correct. That is probably the biggest unkown question for me.
Under driving the alternator and AC compressor at idle is a bit of a trade off, if you can bump your idle up though its not bad at all. The other side of that, is spining your accessories a little slower at mid-High RPM could actually help reliability. I had never experience any cooling issues with an under drive pulley either but it makes you wonder about flow rates and cooling efficiency. The flip side of that is that under high RPM race conditions, slowing the water pump down a little could reduce potential cavitation and there by improve cooling efficiency.
I have used them on RX7's and I would reccomend them in that application. So I guess I would especially like to here from people who have used them in this and/or a similiar application like the WRX.

Thanks in advance,

Eric

SILVER SURFER

No one has used an under drive pulley on a DSM?

tx evo

iTrader: (7)

I will be installing the Crank Pulley, Sept 13,03. Hope to have some Dyno # with just the new Crank Pulley.

See you there Eric.

gsx95

I have had an underdrive pully on my modded GSX for a few years, never had any problems (well, except for that whole crankwalk thing...).

timzcat

iTrader: (10)

I think it is a fair assumption to say the crankshaft is balanced internally so there is no balance affect. That really just leaves the dampner affect of the harmonic dampner.
One could really go either way. On the one hand, the dampner is there for the reason described in the article. In theory if the crankshaft achieves a good amount of vibration (frequency) it could be detremental to the bearings and the crankshaft itself. Given the Evo crankshaft is a forged peice, fatigue in response to vibration is certainly reduced as compared to a cast crank. This of course doesn't take into consideration the transmittal of the vibrations to other parts of the assmebly including the flywheel. The interesting point to the flywheel is the fact that there is a large disc of relative weight on the opposite end of the crank. The flywheel in itself has no real dampening effect and probably helps to exaserbate the problem of haronics. When you consider the construction of the dampener it is really a half-assed attempt given the cost of quality dampening like a fluid dampner.
I small amount of imbalance in the rotating assemblies (crank, rods, pistons) would only help to increase the potential vibrations.
Given this is a production engine and not truly balanced and the fact that it has a relatively heavy flywheel, it is probably not the best thing to remove the dampening. Additionally, the vibrations that occur with a solid crank pulley will be transmitted to the serpentine belt and through the other accessories on the enigine. While it may not be a great amount of vibration, it will have an impact on the bearings through all of those accessories.
This may be a bit too analytical, but it helps make the arguement against a solid pulley.
On the other hand, how long does one really expect the engine to last? And what is the intended us of the engine?
Obviously this is a performance engine and most of us don't expect it to last forever. Not to mention the other mods such as a lightened flywheel which make the arguement null. Most likely there is some method to determining the size, weight, and elastomer in the crank dampner. Remove the stock flywheel and go lighter then there has to be some impact to vibration. At that point, you might as well go with the underdrive pulley.

Now I've been typing to long and don't remember where I am at.
The issue of reducing the other accessories is really negligible. At about 15% the impact is not that great. The generator can certainly live with it. Yes, it will reduce the AC operation at idle but it doesn't work well at idle anyway, since the fan really doesn't extract enough overall heat to help. Power Steering usually has some reserve capacity at idle.
The water pump is the interesting point here since the capacity was increased on the Evo to improve the cooling efficiency. Just say it was increased 15% over the previous design, then you just eliminated that improvement. In most conditions the cooling won't suffer but if you live in a really hot climate, it could have an impact. Given the turbo application, heat is a much more critical factor since there is more of it (turbo) and more demand on the cooling system.

I am not opposed to the underdrive pulley, it really depends on what you expect to get out of the enigine overall. Longevitiy vs. performance, oldest debate ever. You truly can't have both.

Get that knob yet Silver Surfer?

Noize

iTrader: (24)

I had the Vishnu pulley on my WRX, and it was awesome! Have you looked at the pulleys under your Evo hood, though? There sure isn't a lot of clearance from the frame in there! When I first looked at it, I thought: "What do you have to do, pull the motor to take the pulleys completely out?" Be interesting to see what comes up. The install looks like it would be a major beeotch on an Evo.

SILVER SURFER

Here is another dyno comparison before/after the pulley swap on TXEVO's car. I am not sure exactly why, but the engine actually seems to run smoother at idle and under acceleration with the under drive pulley. Looking at the dyno graphs you can actually see evidence of my seat of the pants observation.
I have run my car extremely hard on a road course imfamous for causing cars to over heat, I saw no differences in in oil/water temps before/after the pulley swap. The AC, power steering, and alternator, also seem to work just as well. As for additional engine wear with an under drive pulley, based on my observations I do not believe that will be an issue on this particular car.
From what I am told, the stock fly wheel is actually very light (around 14LBS), forged and possibly made from chrome moly steel (very durable). For a street/track car I am not really sure you would want to go much lighter, a little extra rotating mass can actually be a good thing for launching, especially in this AWD application.
This is just my own speculation as well, but the small amount of harmonic vibration cancelation provided by the stock crank pulley does not seem adequate to compensate for a potential imbalance in the fly wheel/clutch/motor assembly. Looking at the design, it seems like it is actually trying to reduce vibrations induced from the accesories to provide less vibration mainly at idle. I believe this is more for comfort than reliability, kind of makes sense for production cars.
There are some examples of engines with under drive pulleys showing increased bearing wear. But these examples were not done under any sort of controlled test conditions and the excessive bearing wear could have been caused by a number of other factors. What these reports don't usually tell you is that exsessive bearing wear can also be found on cars that do not use any sort of under drive pulley so....
There are also thousands of cars out there that have run under drive pulleys for many years with no sign of excess bearing wear, so.... When you think about the amount of force and vibration the engine bearings see under load, it's kind of hard to believe that a little 3-4LB 6" disk is going to make all that much difference in bearing wear. I would say that poor bearing lubrication would be a much bigger concern than a small vibration damper.
If your modifying and driving your car hard, guess what it's not going to last long anyway. IMO this mod actually stresses the motor far less than any other mod because your not actually asking the engine to make more power. You are simply diverting some of the wasted energy from the accessories to the wheels.
Bang for the buck this modificaton is hard to beat, and IMO is more likely to help reliability especially for cars driven at high RPM most of the time.

No! They just sent me a message that it is still back ordered and that they are returning my money and canceling the order. So if you know where I can get one.....

timzcat

iTrader: (10)

Sounddomain.com has most of them in stock. My RA96 will arrive today and I will let you know how it is. (340grams)
They also have good prices on them.

Okay here are a couple of pics. The stock knob is 21/4 inches high this knob is 2 3/4 high so it is slightly higher. I have not installed the shifter yet, but on stock hardware you can feel some of the affect of the weight. It is about 11.5 oz. so it is pretty good weight. I used a tap to get the insert started straight and went about half way and the installed it from there. It fits nice on the car with the stock boot.

timzcat

iTrader: (10)

Hmm... Guess I can't edit and add the photo.