Pulley kit have any downsides? Or stick to crank

[stugray]

Originally Posted by z3ro

I think it would be better to have a heavier crank pulley. More mass means more inertia. E=mc2 right?

Actually that is not a joke. Lightening race engines too much can be a huge problem with engine stability.

I ask again: WHY (on a car where every once counts) did the engineers put a heavy pulley on the front? (Hint: dynamic balance).
Why is there a hole drilled on every stock pulley? (balance)

http://www.enginebuildermag.com/Arti...balancing.aspx

"When the counterweights alone can be made to balance the crankshaft, the crank is said to be "internally balanced". If the counterweights are too light by themselves to balance the crankshaft and more weight is needed, an "external balance" can be used. This involves a harmonic dampener or flywheel that has a weight on it in the same position as the counterweight that effectively "adds" to the weight of the counterweight on the crankshaft."

[utekineir]

Elaborate on flywheels please.


Thanks

[Mikem53]

Originally Posted by vgi

any hardware and/or software stock piece is part of the equation and changing it could lead to problems. so what are you doing on this forum as it sounds like you should just enjoy the car in stock form and free dealership oil changes?
the question is what that equation solves - eg many people don't care much about air pollution and noise level and are willing to trade that off for a bit more hp/tq by replacing exhaust parts.
as for the pulleys, a lot of folks have run lightweight pulleys on wrxs and stis without any problems. the throttle response is definitely better, not by much but enough to make shifts easier. i'll take that vs some what-ever engineer theoretical insinuations.

Ignorance is bliss.. Enjoy your car anyway you like..

[Team STILLEN]

Originally Posted by Readytoxplod

I noticed a difference with my butt dyno, other's as well. But I am not an engineer. Do you happen to own one Stugray?
"weighs just 1.2 lbs, 3.7 pounds lighter than the stock OEM crank pulley. This reduction in weight from the crank shaft is equal to removing more than 100 lbs of vehicle weight"
So says Perrin. I say "feel" not to get out of any mindset, but because I actually noticed a difference for a little over 100$, and that's worth it to me.

That is a huge exaggeration of the rule of rotating mass reduction and its dead weight equivalent. There are so many factors when calculating that out.

Lightweight flywheels can make a huge difference.

[zooki]

[ame="http://youtu.be/lj60OAh7O5U"]http://youtu.be/lj60OAh7O5U[/ame]

[stugray]

Originally Posted by utekineir

Elaborate on flywheels please.

Thanks

Rotational Inertia = E = Sum of all Mass * radius^2
Assume a “simple” pulley that is 4 inches in diameter (2 inches in radius) and weighs 4 lbs
For the sake of calculation, assume that all of that weight is concentrated around the perimeter in a ring like a bike wheel.
E = 4lb * 2in-squared = 4*4 = 16 lb-in^2
If we replace the 4lb pulley with a 1lb pulley of the same dimensions
E= 1lb * 2in-squared = 1*4 = 4 lb-in^2
For a difference of 12 lb-in^2! Sounds like a significant change….

Now assume a simple flywheel that is 16 inches in diameter (8 inch radius) and weighs 20 lbs
E = 20lbs * 8in-squared = 20*64 = 1280 lb-in^2
How much weight would we need to shave off of the flywheel to make the same difference as the pulley?
1280 lb-in^2 – 12 = 1268 lb^in2
Doing the above equation backwards is:
1268 = new_weight*64 -> new_weight = 19.81 lbs.

So by taking off 0.19 pounds from the perimeter of the flywheel yields the same change as swapping the pulley.
If you changed your pressure plate bolts to titanium, you could get that much.
Do you think you could feel it?

[kuhlka]

Originally Posted by stugray

No but I have told you that "Pros" would not mess with the dynamic balance of an engine by changing a part that is specifically designed to provide dynamic balance without rebalancing the engine. But clearly that doesnt matter.
Did I mention "VOIDS THE WARRANTY"?

Are you an engineer and a lawyer?

Show me a single stock engine that blew up because someone put a lightweight flywheel or crank pulley on it. That's the evidence Subaru or the dealership would have to provide in court to deny a warranty claim because of a flywheel or crank pulley.

[vgi]

Originally Posted by Mikem53

Ignorance is bliss

Indeed, yet you're still making conclusion. LOL =>

Originally Posted by Mikem53

...I don't know how FA20 is balanced but...

[stugray]

Originally Posted by kuhlka

That's the evidence Subaru or the dealership would have to provide in court to deny a warranty claim because of a flywheel or crank pulley.

All they would do is deny your claim.
It is the OWNER that would have to take the manufacturer to court.

And of course if your shocks fail, they would not deny your claim because of a crank pulley, but they would deny your claim if your main bearings failed.

And I can absoultely guarantee that Subaru or Toyota could make the case that changing the stock dynamic balance can cause engine failure.

[SubiePig]

All these engine internals are all going to be different and every within some spec. Is every engine balanced as an entire rotating assembly from the factory down to the flywheel and crank pulley, or are all the pieces with-in some tolerance individually and put together? I would assume due to manufacturing and assembly that it would be the second of those. If that is the case, the owner replacing the front pulley with one X pounds lighter that is balanced properly then where is the issue?

I haven't looked really close at mine, but are our pulleys like the ones found on the WRX that its just a simple pulley with no rubber in the center of the O.D. for damping?

Thinking about it, though I may be wrong, changing the weight of the rotating assembly at one end or both, not just how balanced the replacement part is would affect the way it vibrates. Is it enough to throw some rpm/load/whatever else based issue causing something to fail from vibration. Those sorts of assembly's would be designed far away from the harmonic frequencies of the total assembly for all the various rotating and load ranges I would think.

When I was still working around Mazdas we never saw any issues on a NA car with a crank pulley, the forced induction guys did see a few experiences but that's a different environment.

[zooki]

Originally Posted by stugray

Do you think you could feel it?

I guarantee "some" people on this forum would swear that they could. They have very finely tuned "butt dynos". LOL

[Simply_the_best]

Originally Posted by Readytoxplod

I had a Perrin crank pulley on my last FR-S (totalled by idiot), and it was one of the best mods I purchased (freed up engine, more responsive).
My question is whether I should stick with the Perrin crank pulley or buy a kit?(alternator etc.)Theoretically the lighter the better right?
I heard of problems starting with the full lightweight system, and wondered if anyone has first-hand experience?
My goals are to have a faster revving car, any hp or torque is welcomed.

I have the BuddyClub P1 set and I absolutely love it. I had the Perrin crank pulley and that was great but something about the P1 set that feels amazing. The BuddyClub set is an underdrive style. So the crank pulley is actually a bit smaller than the factory one. A downside to that is that it changes the charging voltage of the alternator but BuddyClub did their homework with this pulley set and actually made the alternator pulley a bit bigger to make up for the crank pulley being smaller. So the battery still charges normally with zero issues, maybe even a little better. This is NOT just hype, no downsides here. It's your car and your money spend it how you want to.

[OICU812]

Originally Posted by zooki

I guarantee "some" people on this forum would swear that they could. They have very finely tuned "butt dynos". LOL

All the asses that were in my car must have been finely tuned butts then, mind you I never was into un tuned asses anyhow not even as a youngster.

[Simply_the_best]

Originally Posted by stugray

All they would do is deny your claim.
It is the OWNER that would have to take the manufacturer to court.

And of course if your shocks fail, they would not deny your claim because of a crank pulley, but they would deny your claim if your main bearings failed.

And I can absoultely guarantee that Subaru or Toyota could make the case that changing the stock dynamic balance can cause engine failure.

Just throw your stock pulleys back on problem solved and they will still warranty it. It takes like 10 minutes(well, that's how long it took me). Plus I work at a Subaru dealer and the amount of heavily modded WRX's and STi's that come into the shop and they still warranty them. It's mainly the dealer that you go to and the service writer you deal with. If they want to be d**ks they can deny it.

Originally Posted by zooki

I guarantee "some" people on this forum would swear that they could. They have very finely tuned "butt dynos". LOL

I'd gladly give you my keys and let you take it for a ride. Then tell me you can't feel it. Doubt that would be the case.