Pulley FAQ: Read if you are thinking of buying one!

[Unabomber]

Pulley FAQ

The primary purpose of an aftermarket pulley is to reduce the size and/or mass of the stock unit. They serve two purposes: to reduce horsepower loss and increase throttle response. Notice the use of "reduce horsepower loss". Pulleys DO NOT add horsepower, rather they free up horsepower due to the reduction of rotational mass.

HP gain is 5-10HP. These HP figures are a range as there have been very few before/after dyno runs with lightened or under driven pulleys.

What is a lightened pulley? Generally, it is an exact copy of the OEM pulley only CNC machined out of aircraft grade aluminum and powder coated for corrosion protection and aesthetic appeal.

What is an under driven pulley? This is a pulley that mimics the function of the OEM unit, but is smaller in diameter. This will reduce the duty cycle of the pulley and proportionally the parasitic drag on the engine.

Are under driven pulleys bad? It depends on the amount they are under driven. Some under driven pulleys can lead to reduced A/C output, lighting problems, stereo problems, and other voltage issues. Some are lightly under driven and some more so.

Isn't replacing the stock harmonic damper (pulley) bad? Subarus do not come with a harmonic damper or balancer like some other vehicles do. For other manufacturers' vehicles, this is a legitimate concern. Proof:

"Thank you for your patience as I checked with our Technical Services Department regarding your message below. They advised that the crank pulley is a pulley and nothing else. It is not used as a harmonic damper/balancer.

Thanks for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again."

Best wishes,

John J. Mergen
Customer Service Department
Subaru of America, Inc.

Are there any downsides to these pulleys? There have not been significant amounts of problems with pulleys. There have been some reports of high RPM issues with pulleys though. These issues tend to happen without regard to type or manufacturer. It possibly stems from rotational issues with the crank position sensor which is located near the pulley. The indication of error is a reduction of the fuel cutoff redline of the motor (false redline). The solution is to reinstall the stock pulley. As with any aftermarket part, even "perfect" ones, sometimes you run into a rogue issue. From research, this is not a widespread issue at all, only an advisory if this situation should occur.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" pulleys on the market. Obviously, there may have been bad pulleys sold, but not enough to report as "bad" overall.

Which pulleys have the best gains? There is no irrefutable evidence that any pulley set has better gains than another. That being said, it stands to reason that a lighter pulley has more gain than a heavier competitor. Under driven would also free up more power than standard size.

Where do I buy a pulley or pulley set? Every Subaru/Import performance store sells pulleys. For purchasing, support your local economy or the NASIOC Vendors.

How hard is it to install a pulley or pulley set? Allow around one hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install a pulley or pulley set? Refer to the pulley manufacturer's instructions. For pulleys without instructions, many rely on the Vishnu instructions for installation. Below are links to some of the better known pulley installation instructions:
Vishnu's Instructions (contained inside the Stage Zero Instructions)
scoobymods.com instructions (with photos)
EDO Performance instructions (with photos)
Perrin Performance instructions (with photos)

Should I reset my ECU after this mod? It is never a bad idea to perform an ECU reset after a mod. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach. Some use the more advanced Vishnu Reset.

Editors Note

This post was created because I wasn't able to find a good pulley FAQ. I came up with the text based on LOTS of searching here. It was also created to be intentionally brand neutral so that it serves as a stepping stone for further research. Upon reading this you should have an idea of what type of pulley best suits your needs. The manufacturer is up to you.

If you find an error in this FAQ, please PM me with factual details and I will update this post. Responses such as, "I have XXX's pulley and it's great!" or "XXX's pulley is all wobbly" are not appreciated here, that is what the Car Parts Review Forum is for.

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[BlueRex28]

Very nicely put together - thanks!!

[rex65]

Another great job
you are on a roll!

[jamz]

Well done. *polite golf clap*

[GT2RS]

Thank you for your patience as I checked with our Technical Services Department regarding your message below. They advised that the crank pulley is a pulley and nothing else. It is not used as a harmonic damper/balancer.

Thanks for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again.

Best wishes,

John J. Mergen
Subaru of America, Inc.

Hey! That e-mail looks familiar!

[Unabomber]

Originally posted by GT2RS
Hey! That e-mail looks familiar!

Mad props to you and sorry for no credit. I hope you will accept late credit anyway. I spent tons of time searching and your email to SOA is the first documented proof about the harmonic balancer issue. I don't think we need to rehash those stories again though. Otherwise, the pseudo mechanical engineers will drown us in their voluminous vocabulary of centrifugal vortices or whatever.

[Paul Sakai]

Bump

Shouldn't this get stickied, somwhere?

[VOLTIS5]

Originally posted by Unabomber
Pulley FAQ

Should I reset my ECU after this mod? It is never a bad idea to perform an ECU reset after a mod. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach. Some use the more advanced Vishnu Reset.

Vinshu Reset...........would this work for a 4EAT?

[Unabomber]

I don't see why not. The keys with this reset are RPM and boost level. The gear you are in plays no part, but they do recommend third as it's the "easiest" to correctly do it.

[VOLTIS5]

interesting...........so which of these procedure would i have to do for a 4EAT?

[Unabomber]

The Vishnu method is the "best" method, so use it.

[sick1.8t]

ok so for a while now i've also been a part of the "not a balancer/just a pulley" bandwagon, but just for arguments sake i'll post up this screenshot of a SAE technical paper written about the EJ series motor written by fuji heavy ltd. employees in 1989.
Take from it what you will, but as you can see the highlighted part decribes a "double mass harmonic balancer" when pointing out the crank pulley. Now this was written in 1989 so the design may have changed since the introduction of the EJ, but I'm pretty sure that nothing as major as the harmonic balence of the motor has been changed.

If anyone wants to host a 17pg, 1.2MB pdf file you all can see the rest, its really quite interesting.




discuss....

[Unabomber]

Originally Posted by sick1.8t

...this was written in 1989 so the design may have changed since the introduction of the EJ....

I'll play devils advocate here too. Lets just say that the pulley IS a harmonic balancer and SOA is a pack of liars. Let's consider this:

Approximately eleventy billion underdrive and/or lightweight non-harmonic balanced pulleys have been sold and used for the last 5 years or so. The amount of grenaded motors is zero. A few users have had issues. Those issues appeared directly after installation and went away the moment the pulley was replaced.

So even IF it is a harmonic balancer: 404 danger not found.

[Eggas]

I had my warranty rejected for my power steering pump (very very hard to turn, making loud noise) because I had a GFB pulley kit on. They said that the pulliers are harmonic balancers are changing those will cause all sorts of issues.

[Unabomber]

That's because the mod had a direct cause/effect. While no one could ever prove the pulley burned up your pump, I can see grounds for warranty denial. They said the pullies are harmonic ballancers because they are ignorant. The average Subaru mechanic has no clue about the mechanical engineering aspect of Subaru engines.

[richde]

Originally Posted by Eggas

I had my warranty rejected for my power steering pump (very very hard to turn, making loud noise) because I had a GFB pulley kit on. They said that the pulliers are harmonic balancers are changing those will cause all sorts of issues.

Dude, you didn't swap the pulley back out before taking it in?

Rich

[frostyTSM]

Una-FAQ-bomer,

I've read a lot of your FAQs and have found them very helpful in recent months. Thanks.

I got a Perrin Crank pulley installed yesterday at my mechanic's shop (not underdrive). They took a bit longer than normal because they wanted to lock the crank shaft in place (not using the "put in 5th gear and step on break" technique) to get just the right torque when putting on the new one.

Anyway, yes there is a harmonic dampener on the stock pulley. Is it needed? I'm not a mechanic, but all mechanics I have talked to have said no so take from what what you will.

Obervations:

• the engine rocks back and forth more when idling
• when boosted, it accelerates smoother (I think the harmonic balancer was causing a spring effect on the crank)
• revs drop much quicker when shifting, and smooth shifts are harder (much like what I've heard about lighter fly wheels)
• the car itself doesn't feel like it is shaking any more than before (when idling)

Edit: harmonic balancer -> harmonic dampener (debate this if you want to)

[jim1969]

I believe there is a harmonic dampener in the stock pulley. That is the rubber insert to reduce vibration. There isn't a harmonic balancer as our boxer engines are internally balanced.

[frostyTSM]

Dampener. Balancer. I know there's a difference but I'm not able to really say one way or the other

(although I will say that dampener sounds more appropriate after seeing it and seeing what it does).

[STi*guy.kiev]

Can the false redline / fuel cut be tuned out by ems? How often does this happen??

[Unabomber]

No it can't be tuned out. It's very rare and only in certain cars. Switching back to OEM makes it go away. I suppose if you went with a pure standalone engine management it would go away as the false redline is caused by the stock ECU.

[WebMasterP]

The video in my pulley review thread might be helpful to this discussion:

http://forums.nasioc.com/forums/show....php?t=1145796

[STix66]

Cliffnotes:
Dont get a pulley.

[theicewall]

Originally Posted by STix66

Cliffnotes:
Dont get a pulley.

Cliffnotes: Why the hell not? If you have a problem with yours for some random unknown reason take it off and your fuel cut issue or cel will go away.

[MSME02wrx]

Originally Posted by frostyTSM

Dampener. Balancer. I know there's a difference but I'm not able to really say one way or the other

(although I will say that dampener sounds more appropriate after seeing it and seeing what it does).

A balancer keeps the amount of vibration to a minimum, where as a damper makes the vibration go away faster.

By the way, a spray bottle makes a good dampener...it dampens stuff. A shock is a damper...it damps vibrations.