To underdrive or not? Pulley Sets
08-24-2003, 12:12 PM
#1
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To underdrive or not? Pulley Sets
Hey guys,.
I've trying to figure out what are the advantages (other than the obvious ie. hp gains) to install an underdrive pulley set. This is because I am deciding between the GFB pulley (underdriven) vs the Perrin Pulley (no underdrive).
I understand that the lower the mass = higher power response at lower RPMs. But what the heck does "underdrive" do? They say it gives 15% more "power"...
thanks!
I've trying to figure out what are the advantages (other than the obvious ie. hp gains) to install an underdrive pulley set. This is because I am deciding between the GFB pulley (underdriven) vs the Perrin Pulley (no underdrive).
I understand that the lower the mass = higher power response at lower RPMs. But what the heck does "underdrive" do? They say it gives 15% more "power"...
thanks!
08-24-2003, 06:32 PM
#2
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Join Date: Nov 2002
Location: Tucson
Posts: 554
Car Info: '02 WRX WRB
Underdrive pulleys reduce the amount of power to the accessories (AC, headlights, stereo, etc.) by changing the pulley diameters. So you will get gains from the lighter pulleys as well as gains from reducing the amount of power your engine has to lose to spin the accessories. Negatives could be dim headlights/interior lights at idle, weaker AC, etc. If you do a search you will find several different opinions on this subject.
08-24-2003, 08:55 PM
#3
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Join Date: Jun 2003
Location: Southern Cal OC
Posts: 28
Car Info: MY 03 WRX
Pulley Change
I have heard that the existing stock pulley is a sort of harmonic balancer and in the long run, replacing it may have a detrimental effect on the longevity of the engine. Any truth to this????
08-24-2003, 09:22 PM
#4
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Even though you might not notice a difference in idle and smoothness of revs, pulleys are dampened for a reason. Not just for regular people looking for a smooth ride. Over the course of a car's 100,000+(hopefully) lifetime, it puts more vibrational wear and tear on rotating parts, particularly the crank. Here's a good article on it:
http://www.dinanbmw.com/html/danger...wer_pulleys.htm
I'm not saying don't get one, but it's something to be aware of for the tuner looking for great reliability from their car. I believe Unorthodox makes a dampened underdrive kit.
7
http://www.dinanbmw.com/html/danger...wer_pulleys.htm
I'm not saying don't get one, but it's something to be aware of for the tuner looking for great reliability from their car. I believe Unorthodox makes a dampened underdrive kit.
7
08-24-2003, 10:00 PM
#5
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i have no experience with pulleys but have read tons of posts from people that had them then taken them off for some reason or another, and a few that had some noticeable negative effects too. I don't recall the specific problems people have had with them, but I'd definitely recommend searching these boards and nasioc.com and tracking down all you can before you decide to to them. I've seen enough questionable threads to make me want to stear clear of pulleys, but i'm also afraid to do anything that i'm not 100% convinced is a reliable mod.
That being said, it also seems that a light non-underdriven pulley might be the safer more reliable way to go than an underdriven pulley.... but i imagine you'd see more power gains with an underdriven pulley of the same weight since you're kicking less power to the accessories and whatnot.
That being said, it also seems that a light non-underdriven pulley might be the safer more reliable way to go than an underdriven pulley.... but i imagine you'd see more power gains with an underdriven pulley of the same weight since you're kicking less power to the accessories and whatnot.
08-25-2003, 03:20 PM
#6
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hmm sounds like I should scour the boards more for possible neg's on pulleys. The general feeling from your advice is slightly ont eh negative side..but the non-underdriven pulley sets sound ok. Less power gains, but better in the long run.
First I heard of "dampening"..gotta scope that out.
the website for the dangers of pulleys:
http://www.dinanbmw.com/default.htm
thanks guys!
First I heard of "dampening"..gotta scope that out.
the website for the dangers of pulleys:
http://www.dinanbmw.com/default.htm
thanks guys!
Last edited by aznfoos; 08-25-2003 at 03:24 PM.
08-25-2003, 04:49 PM
#7
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Join Date: Nov 2002
Location: Tucson
Posts: 554
Car Info: '02 WRX WRB
If you're doing a search, you'll probably find that the boxer engine is naturally balanced. In other words, no dampening on the pulleys is required. When one piston is moving to the right, another is moving to the left, and their movement cancels each other out. You may feel a little more vibration without a dampened pulley, but most people agree that it will have no negative effect on the engine life or performance. My only concern with pulleys is the electricity reduction. I wouldn't worry about the dampening.
08-27-2003, 12:38 AM
#8
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Join Date: Aug 2003
Location: Hampton, VA
Posts: 125
Car Info: '03 Silver WRX
Here's some more information for your research....
http://www.spdusa.com/pulley_kit.htm
http://www.spdusa.com/pulley_kit.htm
08-27-2003, 10:21 PM
#11
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Join Date: Aug 2003
Posts: 152
the GFB set doesn't underdrive your generator. it only underdrives your power steering, AC and water pump so you don't have any electrical problems. Its a "10%" mod though. you can get WAY more bang for your buck with other mods....this one is part of that last 10% of the gains you can get that get more and more expensive for less and less result.
heck, you'd see more difference by putting in strut tower braces, or solid drop links.
heck, you'd see more difference by putting in strut tower braces, or solid drop links.
08-28-2003, 06:40 AM
#12
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Join Date: Feb 2003
Location: 12.9 / 105+
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Car Info: black my03 5mt wrx s/w
under 2700 rpms (ie before boost), i LOVE my gfb set... there's a BIG difference down low. i had to relearn my throttle blips to rev match. the AC does cool a little better off idle, but it certainly worked all summer.
i have yet to hear of someone cracking a crankshaft, which is essentially the ultimate "scary" outcome of these mods.
having said that, decreasing the rotational inertia of the crankshaft assembly (either with pulleys, or flywheels) MAY cause an issue with misfire CELs. the code will be triggered even though there is no misfire.
i haven't seen it mentioned here, but the big difference between underdrive and lightened is the fact that the lightened pulley will cause the car to accelerate faster but will develop the same power output at a given steady RPM (ie. same top speed). the UD pulley will actually decrease parasitic drag from accessories, leading to a higher power output at a given steady rpm (ie. higher top speed). a combination of the two, as seen in the GFB set and others, will yield both advantages.
i picked up my GFB set from a guy used for 90 bucks.
jm2c
ken
i have yet to hear of someone cracking a crankshaft, which is essentially the ultimate "scary" outcome of these mods.
having said that, decreasing the rotational inertia of the crankshaft assembly (either with pulleys, or flywheels) MAY cause an issue with misfire CELs. the code will be triggered even though there is no misfire.
i haven't seen it mentioned here, but the big difference between underdrive and lightened is the fact that the lightened pulley will cause the car to accelerate faster but will develop the same power output at a given steady RPM (ie. same top speed). the UD pulley will actually decrease parasitic drag from accessories, leading to a higher power output at a given steady rpm (ie. higher top speed). a combination of the two, as seen in the GFB set and others, will yield both advantages.
i picked up my GFB set from a guy used for 90 bucks.
jm2c
ken
08-30-2003, 09:49 AM
#14
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Since I got money to spend, and I'm a freak for faster response at lower RPM's (I live for short races in the city), I think I will go for the NON-UNDERDRIVEN light weight pulley.
As I understand, the harmonic dampener is part of my car even if I remove the pulleys, so if I slap on a new light weight pulley set, I will not have to worry about the "wear and tear".
Vishnu, AEM tru-pulley, Perrin, Unorthrodox...whcih ones you guys recommend??
As I understand, the harmonic dampener is part of my car even if I remove the pulleys, so if I slap on a new light weight pulley set, I will not have to worry about the "wear and tear".
Vishnu, AEM tru-pulley, Perrin, Unorthrodox...whcih ones you guys recommend??
08-30-2003, 09:41 PM
#15
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Originally posted by aznfoos
As I understand, the harmonic dampener is part of my car even if I remove the pulleys, so if I slap on a new light weight pulley set, I will not have to worry about the "wear and tear".
As I understand, the harmonic dampener is part of my car even if I remove the pulleys, so if I slap on a new light weight pulley set, I will not have to worry about the "wear and tear".