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Old 03-18-2012, 05:16 PM   #1
beau13990
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Default Underdrive / Lightweight Pulleys: Are they easy to install?

Is this the sort of thing I could do in my driveway? I've got a full set of wrenches, a breaker bar, and so on. I've got a couple of pulley removal tools... my recollection is that one of these is a one-size-doesn't-quite-fit-all unit from AutoZone and the other was application-specific (GM3800) and probably not helpful here. I'm not a mechanic, but I can do a few things on my own (like alternators, starters, timing belts, and fluid changes). I've certainly done accessory belt changes before, on both serpentine systems and the other, horrible kind. I've taken pulleys off before, but it seems to take a lot of physical effort (and I was a lot stronger at the time, too). Maybe my relatively new car (2009 Impreza 2.5i sedan, 24,000 miles) will be easier to deal with than the junkers I've worked on in the past...?

I am curious to hear everyone's thoughts...
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Old 03-18-2012, 05:29 PM   #2
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Hard, no. Useful, not really. A light weight pulley only offers a very small effect.
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Old 03-18-2012, 05:37 PM   #3
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Old 03-18-2012, 05:38 PM   #4
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Originally Posted by Back Road Runner View Post
Hard, no. Useful, not really. A light weight pulley only offers a very small effect.
That's something I was planning to test. That's one of the main points of buying and installing the pulley. If there are real gains in performance or efficiency, that's a benefit, too, but I'm really just screwing around here. Believe me, no one cares if my car is actually fast or not. Perhaps you would suggest I take up golf or something instead...?

Also, I am really wondering what sort of tools I would need to get the pulley on and off. When I removed the crankshaft pulley on my '85 Mustang, for example, I used some tricks involving the starter motor to break the bolts loose. Later, to re-torque these bolts, I just hit a breaker bar with a rubber mallet a few times each, and then hoped for the best. (My pulley never flew off after that.) Is this the sort of thing Subaru owners are doing? Or are their more sophisticated tools and techniques I need to be using?

EDIT: I also might go with a true underdrive pulley, or maybe even try both types. Whether or not the installation is hard makes a difference on that point.

Last edited by beau13990; 03-18-2012 at 05:54 PM.
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Old 03-18-2012, 06:12 PM   #5
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There's math that already tells you. 1st gear from idle to redline, a lightweight pulley will require 1% less energy overall to accelerate the car. If you think 1% is worth the cost, then it's worth it. In 2nd, 3rd, 4th, etc. winding through the gears, the percentage is less.

In comparison, a lightweight flywheel is 11 times this at 11% revving from idle to redline. As you step through the gears, say a full quarter mile run, the total is around 4% less energy needed to accelerate the car. The pulley ends up being about 0.4%. This includes static weight and rotating inertia. Something like a lightweight flywheel is a big deal because the numbers are big. Something like a pulley is a small deal. It's a difference, but you need to weigh the value of the product.

Now if money's no object and you're lightening everything, then it will simply be a part of all the things you're modifying.

Then there's other things...like light weight bumper beams. Oswald makes both a front and rear beam that's vastly lighter than stock, 13 lbs total versus 56 lbs total for both front and rear. And their cost? Around $250 each. A pulley costs $200 and saves a whopping 3 lbs and the rotational inertia savings is not not huge. You can spend a little more on a lightweight flywheel and generate a lot bigger difference. You can spend a little more on bumper beams and generate a lot bigger difference.
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Old 03-18-2012, 06:28 PM   #6
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Cutting static weight =/= cutting rotational weight, but that's a topic for a different thread.

I've been able to remove 3 crank pulleys from 3 different Subarus that are 15-20 years old, with nothing more than a 22mm socket and some PB blaster.

Place the car into 5th, have someone step on the brakes, and break the bolt loose. Spray some PB where the pulley sits on the crank snout and wiggle it off in 15 minutes.

Never needed a pulley remover.
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Old 03-18-2012, 06:44 PM   #7
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It sort of is in many ways. Rotational improvements revolve around a change in rpm which is also a change in straight speed. Static weight change and rotational inertia change both affect the car's change of motion. We can look at the difference as a whole through math. We can look at the different amounts of energy we need to put into the system when we reduce static weight and when we reduce rotational inertia for a particular part.

When you do this math, you see that light weigh pulleys offer pretty little difference in energy required to change the speed of the car. Every little bit helps, but it's useful to first put the money where the big changes are. The big part starts at the heavy flywheel. We're not even buying a whole clutch here although we could. Cost for just a flywheel isn't bad.
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Old 03-18-2012, 07:15 PM   #8
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Quote:
Originally Posted by cal_look_zero View Post
Cutting static weight =/= cutting rotational weight, but that's a topic for a different thread.

I've been able to remove 3 crank pulleys from 3 different Subarus that are 15-20 years old, with nothing more than a 22mm socket and some PB blaster.

Place the car into 5th, have someone step on the brakes, and break the bolt loose. Spray some PB where the pulley sits on the crank snout and wiggle it off in 15 minutes.

Never needed a pulley remover.
I'm dealing with an automatic transmission, though. If I put it in "Park" will your suggestion work? (Or will I just end up sloshing around ATF in the torque converter instead of breaking the bolts loose?)

Quote:
Originally Posted by Back Road Runner View Post
There's math that already tells you. 1st gear from idle to redline, a lightweight pulley will require 1% less energy overall to accelerate the car. If you think 1% is worth the cost, then it's worth it. In 2nd, 3rd, 4th, etc. winding through the gears, the percentage is less.

In comparison, a lightweight flywheel is 11 times this at 11% revving from idle to redline. As you step through the gears, say a full quarter mile run, the total is around 4% less energy needed to accelerate the car. The pulley ends up being about 0.4%. This includes static weight and rotating inertia. Something like a lightweight flywheel is a big deal because the numbers are big. Something like a pulley is a small deal. It's a difference, but you need to weigh the value of the product.

Now if money's no object and you're lightening everything, then it will simply be a part of all the things you're modifying.

Then there's other things...like light weight bumper beams. Oswald makes both a front and rear beam that's vastly lighter than stock, 13 lbs total versus 56 lbs total for both front and rear. And their cost? Around $250 each. A pulley costs $200 and saves a whopping 3 lbs and the rotational inertia savings is not not huge. You can spend a little more on a lightweight flywheel and generate a lot bigger difference. You can spend a little more on bumper beams and generate a lot bigger difference.
One percent is about 2 horsepower; that's in line with what I would expect for a bolt-on mod to a contemporary (i.e. already fairly well-tuned) four-cylinder motor (and I know better than to assume it's 2hp at the peak, as so many people do). The underdrive pulley is worth a little more. People throw around numbers like 5hp and I think that's probably reasonable.

I do appreciate the bumper beam idea. Saving 42 pounds (56lbs - 13lbs) is a weight savings of about one percent, as well. So if the cost is similar to the cost of the pulley, then this is a "toss up." I'd consider doing one or the other, or maybe both, with the deciding factor being ease of installation.

Also, I might favor the lighter bumper beams because they don't involve modifying the motor. I don't thing a lightweight pulley would damage my motor or turn on any idiot lights, but it's certainly more likely than with a bumper beam.
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Old 03-18-2012, 07:31 PM   #9
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Well, the bumper beam also affects handling, lower car weight by a bit and lower rotational inertia from a handling standpoint.
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Old 03-18-2012, 08:13 PM   #10
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Quote:
Originally Posted by Back Road Runner View Post
Well, the bumper beam also affects handling, lower car weight by a bit and lower rotational inertia from a handling standpoint.


It's not rotational inertia if it's not rotating. The bumper would be "sprung weight"

Like I said, for another thread.

You can get a KB light weight crank pulley and simply bolt it on, for $85. No pulling the engine, bolt it on and drive.

Yes, a flywheel will be a much larger gain, but it's also a pain in the ass by comparison.
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Old 03-18-2012, 09:22 PM   #11
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Originally Posted by cal_look_zero View Post
Like I said, for another thread.

You can get a KB light weight crank pulley and simply bolt it on, for $85. No pulling the engine, bolt it on and drive.
So I do not need a pulley removal tool? And if I put the 4EAT in park and apply the parking brake, I will be able to crack the pulley bolts without undue effort? (I'm a 35-year-old male in OK health with hand tools, i.e. wrenches and a breaker bar.)

(It's no problem if you don't know, these are just the questions I still have...)
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Old 03-18-2012, 09:35 PM   #12
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No special tools but you will have to do the starter trick. Use a heavy hammer on the breaker bar to put it back lock tight helps.

Last edited by mod maniac; 03-18-2012 at 10:29 PM.
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Old 03-18-2012, 09:58 PM   #13
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No special tools but you will have to do the starter trick. Ust a heavy hammer on the breaker bar to put it back lock tight helps.
Thanks, that's basically what I was wondering about. Presumably these tricks are effective, so long as the crank pulley doesn't fly off later.

It's funny, though, how people say "it's a simple bolt-on" when there's actually a fair amount of practical knowledge involved. I would not have even suggested the "starter trick" except that I've done it before. I guess that's just the difference between the Internet and real life LOL.

The only things I am still wondering about are, first, whether to underdrive, and second, whether or not there is any chance that any of this will turn on my "Check Engine" light or otherwise affect the integrity of the car. I'm thinking the answer is "no" for the lighter pulley and "maybe" for the underdrive pulley.
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Old 03-18-2012, 10:33 PM   #14
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No it shoudn't turn on the light. if you underdrive sometimes they won't charge at idle. If you don't live in the city no big deal. You get more gains if you underdrive.
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Old 03-19-2012, 01:11 PM   #15
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Quote:
Originally Posted by cal_look_zero

It's not rotational inertia if it's not rotating. The bumper would be "sprung weight"

Like I said, for another thread.
he means rotational in terms of reducing weight from the ends of the chassis, thereby reducing its rotational inertia (aka resistance to rotating in a corner )
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Old 03-20-2012, 01:33 AM   #16
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Quote:
Originally Posted by mod maniac View Post
No special tools but you will have to do the starter trick. Use a heavy hammer on the breaker bar to put it back lock tight helps.

The starter "trick" is downright dangerous. You could just remove the access cover for the flexplate/ tourque converter, and use a large prybar on the teeth of the flexplate. Voila, the crankshaft will be locked in place and you can loosen/torque the crank bolt as needed.
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Old 03-20-2012, 02:03 AM   #17
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You could just remove the access cover for the flexplate/ tourque converter, and use a large prybar on the teeth of the flexplate. Voila, the crankshaft will be locked in place and you can loosen/torque the crank bolt as needed.
What would I be using to interface the "large prybar" with "the teeth of the flexplate?"

Are you suggesting that I just shove a large prybar into my crankcase and use it as a sort of wedge?
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Old 03-20-2012, 02:16 AM   #18
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yes or a large screw driver, that is actually the subaru-approved way to do it, its why that hole is there.

i find its easier to put it in gear/park and have a friend step on the brake.
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Old 03-20-2012, 02:22 AM   #19
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Quote:
Originally Posted by beau13990 View Post
What would I be using to interface the "large prybar" with "the teeth of the flexplate?"

Are you suggesting that I just shove a large prybar into my crankcase and use it as a sort of wedge?

Not the crankcase man, the transmission bell housing.

The flexplate (or perhaps the torque converter itself) has teeth in it to mesh with the starter. A prybar set into the "observation hole" as I call it, and wedged against those teeth is more than ample to hold the crankshaft stationary.

I cannot for the life of me find a picture of the "observation hole" on Google. Maybe I'll take one of my own car tomorrow.
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Old 03-20-2012, 08:40 AM   #20
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^ yeah its not very easy to find.. the first time i looked i gave up and stuck it in gear
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Old 03-20-2012, 10:44 AM   #21
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Originally Posted by aesthetect View Post
^ yeah its not very easy to find.. the first time i looked i gave up and stuck it in gear

That's the thing, he's working with an automatic, and no matter what gear he puts it in, even park, the crankshaft will still not be held in place by the transmision.

I went through this before on a friend's car, and that's how I discovered the "observation hole" method.
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Old 03-20-2012, 12:16 PM   #22
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FWIW, I only needed a strap wrench to hold the pulley whilst undoing the bolt on my 09 4EAT.
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Old 03-20-2012, 06:16 PM   #23
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check out boxer4racing...has some more options for pulley kits, only cause ive never heard of underdrive
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Old 03-22-2012, 03:20 AM   #24
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Ok I have a lightweight pulley on my car... I noticed a little difference. I would not suggest doing an under drive pulley. I have heard that they cause problems... To get the pulley off you need a chain wrench and a 7/8 socket with a nice breaker bar... then when you get the bolt off you take 2 flat screwdrivers and slide them behind the pulley and start wiggling them gently to pry the pulley off. Let me know if you have any problems... BTW I have a agency power pulley that iI got for about $100
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