Perrin Light Crank Pulley

[elninoalex]

Wow, the difference is really noticeable. More than I was hoping for. This thing really jumps off the line now. It doesn't underdrive the components, its just lightweight. It cost $130 and took about 20 minutes to install. And I even took out my radiator when I didn't need to. It probably wouldn't do as much for an AT as for MT, but probably still pretty good.

Stephen

[Phast SVX]

thats my next modification, sounds good to me!
phil

[mbtoloczko]

Originally posted by elninoalex
Wow, the difference is really noticeable. More than I was hoping for. This thing really jumps off the line now. It doesn't underdrive the components, its just lightweight. It cost $130 and took about 20 minutes to install. And I even took out my radiator when I didn't need to. It probably wouldn't do as much for an AT as for MT, but probably still pretty good.

Stephen

Any thoughts about the lack of harmonic balancing with the lightweight pulley?

[Chicane]

Don't worry about it, and do a search on it. There've been topics ont his in the past.

- Rob

I'm running an RVM underdrive pulley. It made a performance difference, and made the engine sound a little different too. I havent noticed any problems.

Mike

[mbtoloczko]

Originally posted by Chicane
Don't worry about it, and do a search on it. There've been topics ont his in the past.

- Rob

I've read all the old posts, and I don't recall having read one that convinced me that using a lighter weight pulley was safe in the long term.

[NomadTW]

the stock pulley does not have a harmoic ballancer

no subarus do

the boxer design is inherently ballanced and does not need harmonic ballancing

Originally posted by NomadTW
the stock pulley does not have a harmoic ballancer

no subarus do

the boxer design is inherently ballanced and does not need harmonic ballancing

Yes it does. Mine did anyway.

Mike

[NomadTW]

pictures, i need pictures

[mbtoloczko]

Originally posted by NomadTW
pictures, i need pictures

They do have a harmonic balancer. Actually, the more technically accurate term is a harmonic dampener. They are used to dampen and reduce twisting of the crankshaft. A crankshaft seems completely rigid to us, but just like anything made of metal, it can be flexed if enough force is applied. Imagine what happens when cylinders 1 or 2 fire on an SVX engine. They can induce a twist in the crankshaft because the other end of the shaft is attached to a rather large mass that has a big rotational moment of inertia that will resist any change in rotational speed. Every flexible system has a frequency which it will vibrate at, and if the system is not properly damped, a forced vibration at the same frequency as the "natural" vibration frequency will cause vibrations to build in amplitude, perhaps to the point of self-destruction. The Tacoma-Narrows bridge is a classic example of this. The harmonic damper reduces the twisting by adding rotational inertia to the front of the crankshaft, and it dampens the vibrations with the hunk of metal attached to the rubber ring.

I think people get away with removing the damper because boxer engines have a very short crankshaft, and with our motors, the firing order helps to minimize twisting. My feeling is that this does not mean that its ok to toss the damper though. It seems that there are some issues with lightweight pulleys on the Subaru 4 cylinder motors. Check out this thread on NASIOC:

http://forums.nasioc.com/forums/show...n&pagenumber=1

In this thread, several people have reported that around 6500 rpm in their WRX motors, their engines start having problems due to the ECU being confused about the actual RPM of the motor. Removal of the lightweight pulley stopped the problem. It seems to me that our SVX motors with a longer crankshaft could perhaps be more susceptible to such a problem. I would be curious to know if anyone here using a lightweight pulley has noticed any odd engine behavior at higher rpms.

[NomadTW]

dampener makes mroe sense

when you say balancer i think of inline and V engines, that have an actual weight on them to coutnerballance the uneven weight/force of the pistons and shaft.

[mbtoloczko]

I got this link off NASIOC:

http://www.dalemfg.com/dale_026.htm

Its kinda cool; it shows twisting of the crankshaft as function of engine RPM for two different harmonic dampers with different damping characteristics.

Here is the page from NASIOC:

http://forums.nasioc.com/forums/show...y&pagenumber=2

It has a bunch more interesting links on the topic.

[wawazat??]

quoted the founder of a noted cam manufacturer (I believe it was Grassroots Motorsports and Harry Crane) who stated that any vibrations that the crank experienced would render calculations and performance of the camshafts irrelevant. The vibration was passed through the system affecting cam timing and subsequently flow rates.

As Harvey (oab_au) has stated time and time again, these will be detrimental to the longevity of an engine. This is especially critical in an all aluminum alloy engine which likes to rev. High-performance racing engines use harmonic dampeners, OEM performance cars use them, our cars (SVX, RS and WRX) came equipped with them from the factory. Why would you remove it?

Todd

The last time this topic came up I got patronized and talked down to extensively by several members of the board, including several from the other side of the globe. I wouldn't like to repeat that so I'll just throw out a disclaimer... please don't post in response to this thread if you have anything snide or patronizing to say.


Many motors have extreme trouble when you put a lightweight (solid) pulley on them... Miatas are an excellent example. They tend to have serious bearing issues after about 10 or 15k miles without their harmonic damper. Most inline engines have a great deal of trouble with this. V engines are somewhat better, but not great.... while BOXER engines seem to be largely free of the harmonic problems associated with other engine designs.

There are people on NASIOC who have run over FIFTY THOUSAND MILES with a lightweight pulley in place and experienced no issues. We ran one on the DNT project car until the supercharger was installed, and then we went back to the stock pulley for belt gearing reasons. We experienced no issues with the lightweight pulley, which was made by GoFastBits in Australia and came supplied with an alternator overdrive pulley to balance the duty on the alternator.

The hobbyist aircraft community uses EJ and EG series Subaru motors extensively, and have reported good long-term results using underdriven and/or lightweight pulleys on the Subaru motors.

I live in the same town with a major Porsche tuner (ProTech) and I was out there talking with John one day and we brought up the subject of lightweight pulleys. He says they use them in all their project cars unless the owner specifies otherwise... he says they've had no issues on the Porsche boxer motors, for the same reasons that we've seen none on Subaru motors... the horizontal design of the engine helps internally damp first order vibrations, and second order vibrations are nonexistent, the kind one would need a balancer shaft for in traditional inline or V design motors.


There has yet to be EVEN ONE documented case of a lightweight pulley causing any type of engine or mechanical failure on a Subaru.

There are hundreds of such cases in the Miata community.


Different engines, different paradigms. The "accepted wisdom" does NOT hold true in EVERY case. Subaru motors are an exception to the rule on harmonic damping.

[GreenMarine]

Stop paitronizing me Porter!!!! You just broght up Miata's because that's what I drove to Reading!!!! Stop picking on Mazdas!!!!