Underdrive pulley Vs. Stock Diameter Vs. Harmonic Balancer???

[Brodie]

The original Harmonic Balancer on my svx died last week a day before i was bringing it to Bob at Maine Auto Clinic in turner to put my Koni's and some stiffer springs, so I had to get it towed as when it happened it jumped the timing..... so after a new timing belt and new timing covers i've got to replace the problem where this all started. The rubber center of the Harmonic balancer seperated and is junk! it lasted 150,000 miles so I suppose it did its job but this is a common problem with them. what do we recomend as far as replacement? New HB from Subaru (around 200.00) stock diameter (but a few pounds lighter) pulley from motorsport 160.00. or an underdrive pulley from (name your pick) prices range from 40-100

I went with the lighter weight but stock diameter one from Motorsport.

Just wondering what peoples experience with the underdrive pulleys were?

 

[inski]

Mike and I were talking about lightweight pulleys. He has read that sometimes they are to cause of some oil pump failures. Possibly due to excessive vibrations because there is nothing to harmonic dampen anymore. But that wasn't the case on his car. http://xsorbit27.com/users5/subarutunersofmaine/index.php?topic=3096.0

 

[Brodie]

I've heard about engine/crank damage with underdrive pulleys as it is "Under" supplying all of your 12volt accessories, problems with low output at idle premature alternator failure etc. but not so much with the lighter weight stock diameter. at least on the svx motor......it is so well balanced that it really doesn't need the harmonic balancer.....I guess a good comparison would be take a perfectlly balanced wheel and throw 2 (1) oz. weights on it that offset eachother and what do you have ? a perfectly balanced wheel.

but i honestly have no first hand info with anything but the stock pulley, I will follow up when Bob is all through with the car. They do good work over there and treat there customers right.

 

[Evan]

I've heard about engine/crank damage with underdrive pulleys as it is "Under" supplying all of your 12volt accessories, problems with low output at idle premature alternator failure etc. but not so much with the lighter weight stock diameter. at least on the svx motor......it is so well balanced that it really doesn't need the harmonic balancer.....I guess a good comparison would be take a perfectlly balanced wheel and throw 2 (1) oz. weights on it that offset eachother and what do you have ? a perfectly balanced wheel.

but i honestly have no first hand info with anything but the stock pulley, I will follow up when Bob is all through with the car. They do good work over there and treat there customers right.

the best way to do under drive pulleys is to get a lighter weight underdriven pulley then get an overdriven alt pulley as a set. the alt pulley is bigger, but the new crank pulley makes up for it. and any pulley that's aftermarket is going to be aluminum, which is about half the weight (or less) of the stock cast steel piece. so underdriven would mean even less aluminum, but its already a lot lighter. the 0.2 hp gain from going underdriven and gaining all those problems may not be worth it.

as for as balance on the svx motor, its the same as any ej series motor. if a wrx does or doesn't have a problem with an after market pulley, so will yours. the ej series has less second order shaking vibration than an inline 4 design, but its still there. most people say that if you're running a fairly low power setup, you're fine with a lightweight pulley. once you go to a high power-big turbo setup, people are less confident in lightweight pulleys. especially over long milage.

when nabisco is back up i'll post a link to the main thread for pulleys, i posted a scan of an SAE subaru paper just for arguments sake.

 

[Brodie]

I've heard about engine/crank damage with underdrive pulleys as it is "Under" supplying all of your 12volt accessories, problems with low output at idle premature alternator failure etc.

 

[junkyardgabe]

wouldn't a big alt. pulley turn even slower than the stock one.meaning even low voltage

i have the gfb underdrive set up and the alt is downsize to match the crank so they will have the same revolutions as stock

 

[Evan]

wouldn't a big alt. pulley turn even slower than the stock one.meaning even low voltage

i have the gfb underdrive set up and the alt is downsize to match the crank so they will have the same revolutions as stock

correct, i was thinking backwards.

 

[Shorty]

Lightweight pulleys are fine. Subaru balances thier engines internally. They rev much better also.

The complaints I've heard only stem from the fact that people don't torque them to at least 135ftlbs and they come loose, ruining the crankshaft. As long as its tight, no worries.

Also, cheap ones may have an issue of actually wearing the pulley grooves, causing the belt to slip. A wise man just told me that one... ;D

 

[mikebike357]

Remember this thread started talking about the pulley on an SVX... do the same internal balancer theories apply to old scoobs?

 

[Evan]

yeah, its still an ej series engine, the only difference being the thrust bearing location and the svx having 2 extra cylinders.