Lightweight crank pulley

[onabulletride]

Originally Posted by FT-86 SpeedFactory

Straight from Subaru America.

"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.


There is nothing wrong with replacing the crank pulley. If so our race car with 30K miles, countless track miles and more abuse than most cars would see over 150K miles, especially with a supercharger. If true ours would have grenadeed by now, but it hasn't.

Car myths from the 90's.

BTW we run, Lightweight crank pulley, lightweight water pump pulley, lightweight alternator pulley, add a couple pulleys in for the supercharger, lightweight flywheel, lightweight wheels, different rotors, different wheels, different tires, different final gear, which all connect to the rotating mass of the crank. Zero issues...

Originally Posted by Fast_Freddy

The oem crank pulley is indeed a harmonic balancer and there should be no question about it. The only legitimate question is how great the risk is when replacing it with a lightweight AL pulley.


I'm currently running a Perrin LW crank pulley with no worries.

SOA says it's not? Now I'm confused.

[Boofneenee]

Originally Posted by onabulletride

SOA says it's not? Now I'm confused.

I think what SOA is saying is thAt the oem pulleys used in our cars are not used for harmonic balancing or have not been balanced. Therefore, we should not be worried about disturbing the balances of the pulleys when they are replaced with something that weighs different and would otherwise screw with the balAnce.

[Xero-Limit]

We run the raceseng set on our shop car. No noises and no issues, US made here in PA.

[DAN_BRZ]

Originally Posted by wootwoot

The other side of the argument is if they are really just a way to cut cost then why do the auto and manual FRS have different crank pulley's? Wouldn't it save more money to use the same pulley? Seeing as how they are just pulleys and all...Same is true of the WRX and STI. Different pulleys.

hey woot, there is absolutely no difference between the auto/manual crank pulley, part #s are exactly the same in the catalogue.

[onabulletride]

Originally Posted by Boofneenee

I think what SOA is saying is thAt the oem pulleys used in our cars are not used for harmonic balancing or have not been balanced. Therefore, we should not be worried about disturbing the balances of the pulleys when they are replaced with something that weighs different and would otherwise screw with the balAnce.

Yeah that was my impression as well. I just wanted to find out what fast Freddy's response was since he seemed pretty sure it was in fact a harmonic balancer.

Sent from my XT1080 using Tapatalk

[wootwoot]

According to Go Fast Bits (taken from ft86 speedfactory web pag):

"Why no Harmonic Balancer?
A better name for a harmonic balancer would be "torsional dampener" since its main task is to absorb the rotational pulses inflicted on the crankshaft by the pistons. Most often it is incorporated into the crank pulley by attaching the outer belt drive ring to the inner by means of vulcanized rubber. At the right RPM, it is possible for a resonant frequency to be set up torsionally on the crankshaft. Resonant frequency occurs when the pulses of the engine correspond with the natural frequency of the crankshaft and it ancillary components. However, since factory pulleys are often comparatively heavy (reasons for this are described later) it is actually the large mass (and therefore inertia) of the factory harmonic balancer and flywheel that will help to excite this natural frequency. So by dramatically reducing the weight and inertia of the crank pulley, the natural frequency of the crankshaft is shifted and its ability to self-excite is greatly reduced. So in fact it is the harmonic balancer's own weight that necessitates the dampening, and since the weight of a GFB crank pulley is typically about 20% of the factory component it cannot supply an exciting force significant enough to damage the crankshaft.

An opinion often expressed is "if the manufacturer put it there, it must be there for a reason". However, if you look at it from the car manufacturer's point of view, casting pulleys from steel is very cheap and easy, because they can be produced in large numbers and there is no waste (as opposed to machining them from billet). But because the resulting pulley weighs significantly more than one made from aluminium alloy, it requires dampening.

Manufacturers will always build cars (even high performance cars) to suit the widest possible selection of driving scenarios and drivers, which means there are always compromises. The weight of the flywheel and pulley also affect how fast the revs drop between gear shifts, and a production car is designed to only allow the revs to drop fast enough for average shifts. If you hurry the shift the revs will be too high for the next gear, resulting in a sharp jerk as the momentum of the engine transmits through the drivetrain. Reducing the engines' inertia with a lightweight pulley kit allows faster and smoother shifting.

When looking at high performance engines such as those found in Honda VTEC equipped cars and the S2000, it is obvious that manufacturers do understand the benefits of reducing engine inertia, and have utilized lightweight pulleys to help the power output and responsiveness without the use of a harmonic balancer.

However, this is not the case for all engines, many of them do require the use of the harmonic balancer to prevent failure. Skylines with the RB20, 25 and 26 are a good example of this, which is why we don't make a pulley kit for them. The pulley kits we do make are for engines that do not rely on the balancer to any significant degree."

Once again, if this is the case, why do we see different pulley weights on the auto and stick (FRS)? And the WRX and STI? Seems like it would be easier for the OEM just to make a lighter pulley in the first place rather than making a heavy pulley and dampening it because of its mass.

But if they were not good for the engine, these guys wouldn't make them..... Right? But there are no recorded engine failures caused by solid pulleys! Oh the confusion!

Again, just pointing out this debate runs deep.

[wootwoot]

Anyone think to email Subaru and ask again?

[Xinshadow]

Originally Posted by wootwoot

According to Go Fast Bits (taken from ft86 speedfactory web pag):

"Why no Harmonic Balancer?
A better name for a harmonic balancer would be "torsional dampener" since its main task is to absorb the rotational pulses inflicted on the crankshaft by the pistons. Most often it is incorporated into the crank pulley by attaching the outer belt drive ring to the inner by means of vulcanized rubber. At the right RPM, it is possible for a resonant frequency to be set up torsionally on the crankshaft. Resonant frequency occurs when the pulses of the engine correspond with the natural frequency of the crankshaft and it ancillary components. However, since factory pulleys are often comparatively heavy (reasons for this are described later) it is actually the large mass (and therefore inertia) of the factory harmonic balancer and flywheel that will help to excite this natural frequency. So by dramatically reducing the weight and inertia of the crank pulley, the natural frequency of the crankshaft is shifted and its ability to self-excite is greatly reduced. So in fact it is the harmonic balancer's own weight that necessitates the dampening, and since the weight of a GFB crank pulley is typically about 20% of the factory component it cannot supply an exciting force significant enough to damage the crankshaft.

An opinion often expressed is "if the manufacturer put it there, it must be there for a reason". However, if you look at it from the car manufacturer's point of view, casting pulleys from steel is very cheap and easy, because they can be produced in large numbers and there is no waste (as opposed to machining them from billet). But because the resulting pulley weighs significantly more than one made from aluminium alloy, it requires dampening.

Manufacturers will always build cars (even high performance cars) to suit the widest possible selection of driving scenarios and drivers, which means there are always compromises. The weight of the flywheel and pulley also affect how fast the revs drop between gear shifts, and a production car is designed to only allow the revs to drop fast enough for average shifts. If you hurry the shift the revs will be too high for the next gear, resulting in a sharp jerk as the momentum of the engine transmits through the drivetrain. Reducing the engines' inertia with a lightweight pulley kit allows faster and smoother shifting.

When looking at high performance engines such as those found in Honda VTEC equipped cars and the S2000, it is obvious that manufacturers do understand the benefits of reducing engine inertia, and have utilized lightweight pulleys to help the power output and responsiveness without the use of a harmonic balancer.

However, this is not the case for all engines, many of them do require the use of the harmonic balancer to prevent failure. Skylines with the RB20, 25 and 26 are a good example of this, which is why we don't make a pulley kit for them. The pulley kits we do make are for engines that do not rely on the balancer to any significant degree."

Once again, if this is the case, why do we see different pulley weights on the auto and stick (FRS)? And the WRX and STI? Seems like it would be easier for the OEM just to make a lighter pulley in the first place rather than making a heavy pulley and dampening it because of its mass.

But if they were not good for the engine, these guys wouldn't make them..... Right? But there are no recorded engine failures caused by solid pulleys! Oh the confusion!

Again, just pointing out this debate runs deep.

Good info! I'd also point out that the factory pulley is pretty crappily made, mine had a lot of small burrs here and there, particularly around the bolt holes. For an item that's supposed to act as a balancer/supress NVH, you'd think they would put more care into making it smooth and uniformly weighted. The Perrin pulley has much better machining, so there is that to consider as well.

[dave77]

Argh, whenever I think this issue is settled I hear the other side of the argument again. I have a perrin pulley but don't have it installed yet. I keep hesitating.

[dave77]

Word. But I think that the oem pulleys are so heavy b/c they were probably cheaper? They could have hypothetically put in perrin pulleys on all the cars, but think about the increased cost on thousands of cars. I wonder how much the oem pulley cost for Toyota, like $10 per car? And what would Perrin charge for all those, a reduced price of $50 per car? Or Toyota/subaru could have designed their own lightweight one but maybe that would add too much to the cost. That's how I think about it. But I'm also making all those numbers up.

Originally Posted by wootwoot

But if they were not good for the engine, these guys wouldn't make them..... Right? But there are no recorded engine failures caused by solid pulleys! Oh the confusion!

Again, just pointing out this debate runs deep.

[stugray]

If you look closely at the factory pulley you will see a hole machined into it near the perimeter on the front.
My assumption is that this hole is put in place when the rotating assembly is balanced at the factory.

Why would anyone want to upset the factory balance for a imperceptible increase in HP or a negligible decrease in rotational inertia?

NOW if I was to build an engine from the ground up I would definitely put in a lighter pulley AFTER a lightened flywheel & clutch, lighter Con rods, pistons, and possibly lightened crank (the pulley has the LEAST effect on rotational mass of any of those other things) THEN I would have the entire rotating mass balanced.

[dave77]

Because it's pretty cheap and easy to do. (as long as it doesn't upset the factory balance, then it's like why not?

Originally Posted by stugray

Why would anyone want to upset the factory balance for a imperceptible increase in HP or a negligible decrease in rotational inertia?

[wootwoot]

Originally Posted by DAN_BRZ

hey woot, there is absolutely no difference between the auto/manual crank pulley, part #s are exactly the same in the catalogue.

Really? I thought Perrin claimed that you saved an extra pound when swapping your pulley on a manual vs auto. Assumed they had to be different weights because of this. Perhaps Perrin was incorrect? I will dig through some threads and see....

[wootwoot]

Originally Posted by dave77

Argh, whenever I think this issue is settled I hear the other side of the argument again. I have a perrin pulley but don't have it installed yet. I keep hesitating.

Lol.... Same here.