Review: Grimmspeed lightweight crank pulley for BRZ and FR-S

Grimmspeed may be late to the lightweight crank pulley game but I’m glad it’s finally out. When I saw the group buy thread on FT86club, I jumped on it immediately. So was it worth the wait?

The Grimmspeed crank pulley isn’t that much different from its competitors. It comes in a range of colors (I opted for the red) and weighs in at 1.1 lbs. For comparison, the stock pulley weighs 4.4 lbs. Although it’s weight saving is minimal, I was surprised to find that it does make a noticeable difference in my BRZ’s behavior.

If you’ve read anything about lightweight crank pulleys, then you’ll know that the primary concept behind them is to lighten the rotational mass on the crankshaft, making it easier for the engine to rev up and down. I’m putting emphasis on the revving down aspect of the crank pulley which I’ll get back to.

Installation

If I’m being completely honest, I was slightly terrified about installing the Grimmspeed pulley by myself after reading this nightmare thread about the crankshaft spacer falling out during installation. I also didn’t have a breaker bar so I knew removing the crank pulley bolt would be a bit of a challenge. For an in-depth install guide, check out this great guide by Enigmus.

In reality, the installation was pretty straightforward and took about 20 minutes of actual work. I also worked on a cold car that had been parked overnight. This makes sure you won’t get burned by the engine and that the bolt and spacer o-ring aren’t going to be expanded.

Start by removing the intake box and the inlet tube so you have room to work. Be careful unplugging the MAF sensor and remember to plug that in afterward. With the intake removed, it’s time to get to the fun part. Take the belt off the crank pulley by moving the tensioner pulley clockwise. The belt slides right off with the tensioner pulley out of the way. If you have a manual transmission, put the car in 6th and yank on the handbrake extra hard to make sure the car doesn’t move. If you have an automatic transmission, you’re going to need to pick up a crank pulley tool to keep the pulley in place while you break the bolt.

Since I didn’t have a breaker bar, I ended up improvising with a beefy ratchet, 22mm socket, and a 3 foot long metal tube as an extension for more torque. I was able to break the bolt just fine with this set up but it was quite a challenge. There’s still quite a bit of play on the crank pulley even with the car in 6th and the e-brake pulled. The bolt wasn’t giving since it was still moving so I stood on the brakes while my dad broke the bolt off. This bolt takes a lot of force so don’t be polite with it.

I took extra care removing the stock pulley to make sure the spacer didn’t come off with it. I just wiggled it back and forth to loosen it before taking it off. You can also keep the bolt still threaded on while you wiggle the crank pulley off to make sure the crank spacer stays in place.

Put the Grimmspeed pulley on and lube up the crank bolt before putting it back on. You’ll want to lube the threads and the bottom of the collar with motor oil before torquing it down. Get your torque wrench and torque the bolt down to 94 ft-lbs.

Place the belt back on all the pulleys and double check your work. Make sure the belt isn’t caught on anything and that it’s seated properly on all the pulleys.

Put your intake back on and pay special attention that the inlet hose is seated properly. If you don’t, you’ll have a vacuum leak and will get a check engine light. Also remember to plug back the MAF sensor. I forgot to do this (d’oh!) and subsequently got a CEL. Luckily the codes were easily cleared using my ODB II Bluetooth adapter and the Torque app for Android.

That’s it! Now start the car and make sure everything’s working properly.

Driving impressions

Getting in the car for the first time after installing the Grimmspeed lightweight crank pulley was eye opening. I didn’t expect it to make much of a difference but it did. I found myself having to add gas a bit earlier while setting off in 1st gear because there’s less rotational mass to keep the engine from bogging. This wasn’t a big deal and I got used to it quite quickly.

Taking the car on a spirited drive revealed that the engine RPMs would rise and fall just a bit quicker. This made rev matching and heel-and-toe a little easier. I always felt that the engine held on to RPMs just a few milliseconds longer than I’d like. The Grimmspeed pulley solved that. It’s by no means a night and day difference but is noticeable.

Another thing I noticed is that the idle dip that our cars are known to have has mostly gone away with the Grimmspeed pulley. Before, the car’s idle would dip from 700RPM to 600RPM, causing the car to shake while at a stoplight. It’s annoying and happens more when the air conditioner is on because of the drag on the engine.

Overall, for the price, the Grimmspeed lightweight crank pulley is another “must have” for the Subaru BRZ or Scion FR-S. Sure, it may be a “poor man’s lightweight flywheel” but it’s much easier to install and the improvement is noticeable. Highly recommended.

Buy now: Grimmspeed Lightweight Crank Pulley – BRZ/FRS, 2015+ WRX

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