I keep hearing mixed things about lightweight engine pulleys being unhealthy for an engine, but I can't seem to find a clear explination of whats bad or what it could do. I understand the basic principal is just a weigh reduction on the drivetrain component of the engine, is there more to be concious of?
here's the info i collected... please correct me if im wrong the pulleys and flywheel cortribute to rotational mass for the engine... theoretically, the lower the mass, the lower the inertia and the engine will rev faster... also since less work is done turning the crank shaft, more power can be put to the ground... lightening the rotational mass has some drawbacks... first of all, lowered rotational inertia will increase the chance of the engine bogging and stalling out unless the clutch is dropped slowly or at high rpm... also if the mass is reduced too much, misfire issues might arise
well, I'm 4eat, so the former isn't a probelm since the torque converter replaces it... but on the latter, would that mean a flash tune would be appropriate with a pulley install? (meaning is that something tuning can overcome?)
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 is a link to some of the better known pulley installation instructions: scoobymods.com instructions (with photos) this info is from Unabomber a NASOIC member.
now I DID dive into nasioc, but didn't see this because i was looking for 'pulley problems.' So i would guess a mod like this would be for throttle response more than peak power, right?
i have an AEM alternator underdriven pulley..it helped with the revs..made it a bit easier to rev match/heel toe..did not feel any noticable power though
i felt the crank pully gave me better throttle responce. the stocker is alot heaver than the replacement. at least on my car it was. like a 5 to 10 pound difference. mine is also underdriven. im happy with the results. i think the more mods you have the bigger the difference it will make. it was kind a pain to get the stock one off for me cause i did this mod after putting 55k on the car.
I've also heard that the crank pulley is next to impossible to get out on the 4EATs. A lightened crank pulley is much akin to adding a lighter flywheel; on a pulley it is a couple pounds lighter but due to the smaller radius you have almost the same reduction in inertia that you have dropping 10lbs off of a flywheel. The lower inertia is what will cause your car to rev quicker, but also potentially stall quicker (not really an issue with the auto). As far as on an automatic it might allow you to reach your stall point quicker for drag racing or what have you.
which would mean I wouldn't have to scurry up to stage so i could Vaccuum brake to stall... mmm. I'll consider this closely. whats so hard about the install? or should i just go ask Porter? ;p
I just remember somebody last year on ClubWRX complaining about not being able to remove the stock pulley, not too much past that. I'm not exactly sure about the stall point, reaching stall speed is more of a heat related problem but I'm sure that it wouldnt hurt.
mine was really hard to remove lil pbblaster and 2 pry bars (1 ontop and 1 one the bottom) worked fine for me. a large flat head will work also. as far as getting it off i dont really see what the diff would be between an auto over a manual.