Projects & Mods - Unorthodox Underdrive Pulley

:. Projects/Mods .:. Underdrive Pulley .:

Tools	Get From:
·14mm socket and rachet	any hardware store
Materials:
·Underdrive crank pulley	Extreme seems to have the best prices...

Introduction
Almost everybody knows the theory behind underdrive pulleys, so I'll skip the long-winded explanation. In short, these pulleys allow a bit more power to be sent to the wheels, that was previously lost driving the accessories of the engine. Lighter weight, (like a lightened flywheel) means it is less mass for the engine to accelerate. As such, like a lighter flywheel, this change will be primarily noticable in 1st and 2nd gear.

Installation Notes
It doesn't get much easier than this. Jack the car up in the air, pull off the left wheel, and undo the four 14mm bolts on your stock crank pulley (aka Harmonic Damper). Put the new underdrive pulley in place, and adjust your belt tensioners on the alternator (and A/C, if you have it), and you're done.

You will note that the locating keyhole for on the Unorthodox pulley is slightly oblong, as opposed to the factory one which is round. This allows for a little bit of slop in attaching the pulley. I put the pulley on with the hole centered.

For the very studious, if you have a timing light, you can check before and after the procedure to ensure that your base timing readings are still the same. With my pulley installed as indicated, timing remained at 8* BTDC.

Testing and Results
First, some static numbers:

Weight:
Stock crank pulley: 76 oz (4.75lbs)
"Old" style: 16oz
"New" style: 17oz

Size (diameter):
Stock: 6 1/8"
"Old": 4 7/8
"New": 5 5/8

And here, some HP and subjective results, measured with a G-tech computer. (at least it's something, right?)

Constants:

same section of road, direction
small cool-down lap after each run, same each time
car weight entered into g-tech was 3070
did not move gtech between experiments
short shifted 1st and took second to redline each time.
during daylight, did 2 runs with headlights, 3 without to see if it affected the readings
16psi (to reduce effects of knock, leaks, etc etc)
same amount of gas
"rich" autocross tune settings
reset ECU before each group of runs
ambient temp 63*F

Results:

Before:

Run 1: 241
Run 2: 247
Run 3: 241
Run 4: 235
Run 5: 240

After:

Run 1: 257
Run 2: 252
Run 3: 243
Run 4: 245
Run 5: 241 (extensive knock)

Analysis
Throwing out the highs and lows, those numbers give an average gain of just under 8hp at the wheels. I had intended to test the old-style small diameter unorthodox pulley, but curiously enough, it did not fit on my crank. After reading a bit on Unorthodox' website, I came across the following text, which leads me to believe the gains would have been minimal, at best:

"...These gains are obtained in two ways. First, and most important, is the weight loss. There is an average of 2.7 HP gained from every pound lost off the crank shaft. With the lighter accessory pulleys, as much as 15% to 30% more power can be found. 85% of our gains are from weight loss.

The rest of the gains are from underdriving, which accounts for about 15% of the total gains. We do not push underdriving for two main reasons. Our main reason is to keep charging systems, air conditioning, power steering, and water pumps moving fast enough for every day driving. Second, not much horsepower is gained from extreme underdriving. "

I got the pulley as part of a set some fellow was selling. It should be noted that the Unorthodox water pump/ps pulley cannot be installed with the engine on its mounts - you have to unmount it and move the motor up or down. I decided not to try it, since the weight difference was negligible with the stock pulley.

Impressions
To be perfectly honest, I had a difficult time telling that the pulley was installed. The motor maybe revved a bit more easily, but really it was a pretty transparent change. No dimming of the headlights at idle like with the smaller diameter pulley (friend of mine has one), just, apparently, a few more ponies on the top end. Oh, and it looks purty.

Final Pricelist

Item	Cost	From
Unorthodox Pulley Set	$200	Club DSM Member
Sell Accessory Pullies	-$80	Club DSM Member
TOTAL:	$120