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#108: 03-02-2014, 01:35 PM
Lightweight Crank Pulley - GrimmSpeed
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Title: MPG Tuner
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Car: '05 LGT, '12 OBP, '00 G20+T
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I've been eyeballing one piece lightweight crank pulleys since I did the timing belt on the Forester and saw how heavy stocker is. Plus they tend to separate and cause some destruction.

List of aftermarket pulleys and information: Crank Pulley List (Price, Weight, Part #'s)

I went with GrimmSpeed due to the heavier weight, it doesn't cause CEL's like others might when you use it with a lightweight flywheel. Plus Grimmspeed has timing mark and sells a kit for 08+ stretch belts (that I might convert to).

For those that are curious, GrimmSpeed says the pulley has timing marks, they mean mark. It took me 5 minutes to find that single mark...

I was under the impression that the pulley would be 2.6lbs, it feels heavy and is a very high quality piece, to my surprise it came out to be 2.05lbs.

Stock Pulley weighs a hefty 5.65lbs

GrimmSpeed vs Stock pulley

Start removing all of the parts in the way, I was able to do it with the intake and rad fans in place.

Undo the lock bolt then unscrew the alternator tightening bolt, you will have to push the alternator down to remove the belt.

Same deal for AC, undo the idler pulley bolt, that will allow it to freely travel, then unscrew the AC belt tightener.

After the belts are off get a 22mm socket and a breaker bar. Make sure your handbreak is tight and put the car in 5th gear. Use the breaker bar to loosen the bolt, then remove it.

I used a big screw driver to slowly wiggle the crank pulley off

Notice the circular cut in my timing belt cover, also notice the glue on the AC plug. Looks like this car suffered from the crank pulley falling apart previously...

Install the new pulley, make sure it goes on the tooth correctly before you begin to tighten it

Manual calls for 33ft-lbs of torque, but then rotating it to 65*-75* which equals to around 100ft-lbs, GrimmSpeed calls for 94ft-lbs. Reason manual calls for the degree deal, is because the bolt might overstretch, if it does even torquing it properly might mean the crank pulley is still loose. I try to use new bolts for piece of mind for this reason.

Reinstall the belts, make sure they are aligned on the crank pulley properly before tightening them or you will shred the belts. Then properly tighten them or they will squeak.


Now the moment of truth, you're $115 in and how much power does it gain you?

Sadly loosing 3.6lbs from parasitic mass gained no power (in 2nd gear), at least GrimmSpeed didn't promise/advertise power gains. Usually lightweight and underdriving pulleys will gain you 5whp or so, guess all the power gain comes from underdriving and not from being lightweight.

I will say the motor did rev up smoother with the new pulley, I'm driving the car around right now to see if city MPG improves any.

At this point I would say only go lightweight if your current pulley falls apart and you need a new one anyway. My opinion may change once I drive the car in a spirited fashion after the MPG test.

Update 04-25-14: After driving for a while, it does seem like this pulley help improve my low end torque and the car likes being in 4th at 30mph a lot more. MPG gain/loss has been neglectable though.
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Last edited by covertrussian; 01-21-2018 at 03:52 PM..
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