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Old 03-18-2012, 07:15 PM   #8
beau13990
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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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