Need Speed

I drive a black 2000 S4 with an APR Stage I EMCS chip, and love every minute of it. But I'm leasing the car so I'm always looking for subtle ways to increase power, without loudly announcing the 'upgrades' to my local dealer. Plus the upgrades for me need to be things I can swap in and out myself. This pretty much limits the changes, excluding things like different turbo, exhaust, etc., so I've started to feel like I've hit the proverbial glass ceiling with the chip boost and K&N filter.

I recently found out about the advantages of swapping the factory crankshaft pulley for a light-weight, reduced diameter piece. A friend of mine owns a Subaru Impreza 2.5 RS, and he is a performance hungry car nut too. He runs a CNC machining shop in Toronto, so he has access to high-tech CAD/CAM hardware.

He did some research and found that you can get about 2.5 to 3.5 HP gain and almost that much torque for every pound of weight you shave off from the hefty factory crankshaft pulley (typically made of cast iron or stamped steel) for normally aspirated engines, and approximately another 20% more gain with forced induction, VTEC, etc.

Anyway, my friend decided to CAD design the pulley for his Impreza and CNC manufacture it from high-grade aluminum in his shop. He managed to reduce the factory cast iron pulley's weight from 5.6 to 0.8 pounds. That's over 80% reduction, and a power gain in the order of 15 HP on his normally aspirated 2.5L Impreza engine! After hearing about the results people started to ask him to churn out a few pulleys for friends and guys in the Toronto Impreza Club. I've seen the product and the responses, and its nothing but the highest quality (with CNC the tolerances are 0.0002").

But the proof is in the pudding, so I drove his Impreza RS before and after the pulley swap, and the change is very apparent. The engine noticeably pulls stronger and revs better! So a light went off in my head, looked at my S4 crankshaft pulley (which is even heftier than the Subaru factory piece, needless to say), and decided I wanted one. We're going to take measurements for CAD from my pulley in the next couple of weeks, and also another guy with an A4 at his work.

I can't wait to get my hands on this baby! I wanted to post this to see if anyone's interested in the results?

Peter
2000 S4
APR Stage 1, K&N

LCP

Keep us posted.

KgS4

which reduced the weight from the stock of 21lbs to 8 lbs. That is a whopping 13 lbs of reduction of mass directly off the crankshaft, but on the dyno it only added about 4 hp on a 250hp car. Not to mention the flywheel is larger in diameter which has a greater effect on rotational HP loss (weight farther from the center), so you would think reducing the crank pulley weight would have even less effect. If you think about the hundreds of lbs of drivetrain mass between the crankshaft and the pavement (transmission, driveshafts, wheels/tires, etc.), I can't see knocking just a few lbs off it with a lighter crank
pulley is going to do alot.

Are you sure he didn't also increase the diameter of the crank pulley, thus slowing down all the accessories (alternator, etc.)? Because this is the common purpose of a 'pulley change' for more power, and it is usually quite effective,
although it can have some unwanted side effects (less than full charge on battery at idle, etc.)

ryoung

Reducing the weight of the pulley does not add anything at all to motor horsepower. What it does do is reduce the weight of another "flywheel".

Every time you rev up the motor, you're adding energy that's being stored in your pulley "flywheel" rather than being used to accelerate the car. This does help, but not nearly as much as you're implying. From this change only, I'd be very surprised if you'd notice the difference in a 1/4 mile ET. For those with a technical bent, calculating the amount of energy stored in a flywheel is straightforward. Knowing the amount of time it takes to rev from 4500 to 7000 rpm, for example, let's you calculate how much of the motor horsepower is being used to rev up the pulley rather than accelerate the car.

In my "spare" time I'm the crew chief for a Formula car; and within the rules, we will do everything possible to reduce rotating mass - lightened cranks, flywheel, pulley, CV joints, wheels, ring gear carriers, etc etc. In Formula 1, they'll use a thinner brake rotor for qualifying.

Dr. Mike

Hiya,

I agree with my colleagues here that the hp gains will be minimal. My experience with a pulley set from Unorthodox Racing on a 96 Integra GS-R, 2hp on the dyno. In fact, I got the same hp increase from simply removing the P/S belt (I sold the pulley and just removed the P/S belt for drag racing).

In addition, look at the A4 vs. the Subie you mention or my old Integra. It is a plusher car, with more electronic and electrical accesories. If you go overboard on your alternators ability to charge, you could be firing off VAG codes galore for low voltage.

It is wise when you are doing your calculations, not to simply look at what you want to see- hp increases, you should also do some calculations on how the performance of your accesories will diminish.

Good luck in your endeavor,

Michael

Need Speed

Wow! First of all, thank you for the incredible response. Some of you guys really seem to know your stuff. I forwarded your comments to my friend making the pulleys, which was truly appreciated.

Based on your comments and his response I also did some more research (thanks for pointing out the other sources), and found for instance that Unorthodox claims that the concern about the lightened underdrive pulleys having an impact on the crankshaft harmonic vibration balancing is a misconception. Apparently, the late model factory pulleys have two problems they must overcome as a direct result of their own heft: to reduce audible noises and to provide torsional damping because of their heavy weight. Both of these problems are alleviated by the much lighter and perfectly balanced CNC machined replacement aluminum pulleys.

The other misconception is that the pulleys themselves are harmonic dampers, which again is not true. Apparently, the harmonic damper (if one exists since modern engines don't require one) is a separate piece on the crankshaft snout, attached to the crankshaft accessory pulley. Neither the harmonic damper nor the balance shaft have anything to do with replacing the pulley itself.

They also say that the factory pulley gearing is over-engineered for charging and spinning the other pulleys. In other words, even the reduced diameter pulley provides sufficient charge at idle for the alternator and accessories. However, conceivably you could even keep the same gearing ratio by replacing the other pulleys with smaller ones also.

By the way, my friend started making the parts for himself when he realized that being north of the border in Toronto, he could make the highest quality performance parts and all kinds of creative accessories a lot cheaper than buying them from States, and that still holds true. This way the CNC machined parts like the pulleys, laser engravings, anodizing, etc. can be done for a fraction of the cost of bringing them across the border, given the sorry state of our Canadian dollar. US performance products are starting to get a little steep for us here when you factor in the exchange rate.

In any case, thanks again for all the comments. I'll keep you posted here when my buddy completes more testing, and see how things work out for the Audi and VW parts.

Thanks again everyone.

Peter
2000 S4
APR Stage 1, K&N

Bollinger

Without attacking anyone, right at the beginning of this year the unorthodox pulleys were plugged on several forums (S4 & A6 for sure). They came under heavy fire, probably even more than they deserved.

However, it seems odd that now as then, the initial post from the person plugging the pulleys took a folksy "aw shucks" tack at it and failed to even explain the proper name of the item and how/why it works. Also note that the person who was posting this info before used three different accounts to post the info before, so this may be the same person again.

All this isn't designed to slant you for or against these pulleys, just that if you are considering them, you can do some more research by searching here a little for "unorthodox pulleys" on at least the S4 and A6 forum.

Need Speed

Interesting concept, but I'm actually new to the forum (not to the site), and I only posted 2 messages on this one, this being my 3rd.

Far from trying to discourage anyone from pulleys, I'd rather more people were interested. I did test drive the Subaru, and felt the difference, so I still think it works. I'd still like to get more power out of my S4, so I haven't given up on the idea. Bare with me while I'm working on getting a oulley made and tested.

Peter

Dr. Mike

Hiya,

I'd be interested when I see a dyno of this on a 1.8T before and after install by someone other than the person trying to sell one.

I would be careful of the charging aspect. Unorthodox has done the testing for altenator/accesory charge on their design, not yours. If you wish to offer the part to us and want interest in this, this testing must be done for your part as well. You mention in your original post that you are interested in dealer invisibility for your mods, just because the alternator/accesory charge allows operation and aren't adversely affected doesn't mean VAG codes aren't popping up.

You should check the archives as Steve suggests, if the Unorthodox part is getting bad reviews (fairly or unfairly) you should be aware of this, again, before trying to create interest in your part.

I am not attacking your part, I'd just like some hard and fast dyno numbers on it before I express interest. I can only attest to what I saw on the dyno with another 1.8L motor.

Again, good luck in your endeavor,

Michael

Need Speed

Keep in mind I don't even have a working pulley for my S4 yet, so I'm not offering a part to anybody. I'd just like to get one for me. But when the time comes, I'd like to find out exactly what it does for the car, and if I do I'll post the results.

Good point about the VAG code s though... Remains to be seen.

Thanks,
Peter