GrimmSpeed Lightweight Crank Pulley - New Product Information

[GrimmSpeed]

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ENGINEERED PERFORMANCE.



[SIZE=3]Your factory crank pulley is responsible for transferring energy from your crankshaft to your water pump, a/c compressor and alternator. It does this by way of a rubber belt and it does it's job well. The drawback to the factory pulley is that it's quite heavy. Reasons for this include less expensive manufacturing and using the pulley's mass to smooth out 'noise' in the accessory system (NOT to be confused with functioning as a harmonic dampener, which it does not). The GrimmSpeed Lightweight Crank Pulley reduces the rotational mass of the system, allowing your engine to accelerate and decelerate the rotating assembly more quickly.

Quick Specs

• 78% Reduction in Rotating Mass - weighs 1.1lb vs the 4.9lb OEM pulley
• Machined 6061 T6 Aluminum - high quality, precision construction
• Hard Anodized Finish - ensures a durable finish and resists corrosion
• Removal Tool Mounting - allows the use of the GrimmSpeed Crank Pulley Tool
• Factory Fitment - direct replacement for easy installation

Design
The design process for this pulley ensured that a perfect factory replacement fitment was maintained while performance was maximized. It's a common misconception that the mass of a crank pulley alone determines its effectiveness. The truth is that it's actually the moment of inertia that affects the pulley's ability to improve engine and throttle response. The moment of inertia, in non-engineering terms, is a function of not only the mass of an object, but how that mass is distributed about it's rotational axis. A lower moment of inertia means that less torque is required to spin the crank pulley and, in turn, the crankshaft/engine. Our engineers took great care to keep the already minimal mass as close to the center of the pulley as possible without sacrificing its strength.

The result is a pulley that fits well, looks beautiful and works exactly as intended. From the first test drive, you'll notice smoother operation, faster response and a more enjoyable drive. Much of this is difficult to quantify, but you can see from the datalogs below that when compared to the OEM pulley, the GrimmSpeed Crank Pulley quantitatively improved throttle response.



Another major improvement made is that you'll find the necessary threaded holes to use our Crank Pulley Removal Tool for safe and easy installation and removal. On newer vehicles, cars can simply be put into a high gear to break the crank pulley bolt loose, but as with older chassis vehicles, this bolt will likely become quite stubborn with time. The use of the GrimmSpeed Removal Tool will make removal quick and easy.

Materials
Like any GrimmSpeed product, these pulleys are built to last. Using locally sourced 6061 T6 aluminum billet, the pulleys are machined and measured to verify critical dimensions before being anodized. The bright dip anodizing process that we use ensures a durable finish that will protect the pulley from corrosion. Lastly, each pulley is laser etched with a sharp GrimmSpeed logo.

Performance
Proven performance from a crank pulley can be difficult to quantify, but when you're pulley is meticulously engineered, the results are there. Below is a chart showing the free revving of a stock BRZ equipped with a stock pulley and then a GrimmSpeed pulley. It's easy to see that the engine reaches redline faster and drops to idle faster with the GrimmSpeed Lightweight Crank Pulley installed. That's improved throttle response that you'll appreciate immediately.



Fitment

• 2013+ Subaru BRZ
• 2015+ Subaru WRX
• 2012+ Subaru Impreza
• 2011+ Subaru Forester
• 2012+ Subaru Legacy
• 2012+ Subaru XV Crosstrek
• 2013+ Scion FR-S

Options
Pulleys are available in Black, Blue, Red and our special release Gunmetal color.

[tennisfreak]

Looks awesome!







Waiting for @stugray..........

[stugray]

Originally Posted by tennisfreak

Looks awesome!
Waiting for @stugray..........

Ok:

Originally Posted by GrimmSpeed

Performance
Proven performance from a crank pulley can be difficult to quantify, but when you're pulley is meticulously engineered, the results are there. Below is a chart showing the free revving of a stock BRZ equipped with a stock pulley and then a GrimmSpeed pulley. It's easy to see that the engine reaches redline faster and drops to idle faster with the GrimmSpeed Lightweight Crank Pulley installed. That's improved throttle response that you'll appreciate immediately.

"It's easy to see that the engine reaches redline faster and drops to idle faster with the GrimmSpeed Lightweight Crank Pulley installed"

Umm. NO.
If you look closely at the graph, the rise & fall of RPMs is exactly the same.
The two graphs are only offset ,because they started at slightly different initial conditions.
The SLOPE of the RPM rise falloff is exactly the same for both pulleys which means "no appreciable difference in rotational inertia".

Thank you for posting a graph that so perfectly makes my point.


AND: Mass Moment of inertia Stock 30.42 lbin^2 vs 6.09 lbin^2 for the GS pulley.
Great! SO what is the Mass Moment of inertia of the entire rotating mass?
Assuming that they actually calculated it correctly, see how the mass Moment of inertia of a 4.9lb pulley can be over 30 lbsin^2???

That's a factor of 6X for something so close to the center of rotation.

That means that the mass moment of inertia of the entire ~500 lb rotating mass could easily be in the 3000-10000 lbsin^2 range. (and that is being generous since MOST of the weight of the rotating mas is a LOT further away from the center of rotation than the pulley)
SO changing the pulley makes a whopping:
30.42 - 6.09 = 24.33 lbin^2 in an engine with greater than 3000 lbs in^2?

For a whopping 24.33 / 3000 < 1 % difference? (actually MUCH less as the 3000 is VERY conservative)

Whoo Hoo! I'm sure you can feel that in the butt dyno.

As I have stated before: you will get a bigger benefit by changing the pressure plate bolts from steel to titanium or shed 1 ounce from the timing chains.

Grimmspeed: I apologize. I would not go out of my way to make this type of statement if I had not been called out to do so.

I still think the pulleys look awesome.
If I was building an engine from the ground up I would use these.

[GrimmSpeed]

Originally Posted by stugray

Lots of stuff

Grimmspeed: I apologize. I would not go out of my way to make this type of statement if I had not been called out to do so.

I still think the pulleys look awesome.
If I was building an engine from the ground up I would use these.

Hey, no worries! We'll put our heads together and respond a little bit later today when we've got time to do so properly. At that point, we'll either agree to disagree or we'll update our figures. We very much appreciate your analytical feedback!

Quickly though, for what it's worth regarding the 'butt dyno', I can absolutely identify the difference that a crank pulley makes and I think that a lot of people would agree. That is the same type of commentary that we received when we released our strut tower bar with quantitative data that many argued was negligible. We sent a few of those people free bars with the agreement that they could send them back if they didn't want them or buy them if they wanted to keep them. Not a single person wanted to send theirs back.

Matt Beenen
Engineering

[GrimmSpeed]

Originally Posted by stugray

Ok:



"It's easy to see that the engine reaches redline faster and drops to idle faster with the GrimmSpeed Lightweight Crank Pulley installed"

Umm. NO.
If you look closely at the graph, the rise & fall of RPMs is exactly the same.
The two graphs are only offset ,because they started at slightly different initial conditions.
The SLOPE of the RPM rise falloff is exactly the same for both pulleys which means "no appreciable difference in rotational inertia".

Thank you for posting a graph that so perfectly makes my point.


AND: Mass Moment of inertia Stock 30.42 lbin^2 vs 6.09 lbin^2 for the GS pulley.
Great! SO what is the Mass Moment of inertia of the entire rotating mass?
Assuming that they actually calculated it correctly, see how the mass Moment of inertia of a 4.9lb pulley can be over 30 lbsin^2???

That's a factor of 6X for something so close to the center of rotation.

That means that the mass moment of inertia of the entire ~500 lb rotating mass could easily be in the 3000-10000 lbsin^2 range. (and that is being generous since MOST of the weight of the rotating mas is a LOT further away from the center of rotation than the pulley)
SO changing the pulley makes a whopping:
30.42 - 6.09 = 24.33 lbin^2 in an engine with greater than 3000 lbs in^2?

For a whopping 24.33 / 3000 < 1 % difference? (actually MUCH less as the 3000 is VERY conservative)

Whoo Hoo! I'm sure you can feel that in the butt dyno.

As I have stated before: you will get a bigger benefit by changing the pressure plate bolts from steel to titanium or shed 1 ounce from the timing chains.

Grimmspeed: I apologize. I would not go out of my way to make this type of statement if I had not been called out to do so.

I still think the pulleys look awesome.
If I was building an engine from the ground up I would use these.

I was the one who did the testing, and the one who made this graph, and I must say that you might be interpreting it wrong. I can get why it might looks like the change is only due to an offset, but I think that's because you're looking at the 2 period moving average line, and not the raw data lines that it is based off of. I normalized all the data to start from the same initial conditions, and then averaged three runs (3 stock pulley, 3 GrimmSpeed Pulley), and then plotted them on this chart. I included the moving average line just to help show the difference, although it can be a confusing way to view the data if you don't know what you're looking at.

The testing was conducted the exact same way, and using an OFT to datalog. The OFT is good for about 10 samples a second, and all I did was log time, RPM, and throttle position. This is how I was able to obtain starting points, and using the average of three runs each specifically to prevent seeing results in the form of ONLY a data offset. I did the same for the decel chart (this are actually two charts added together), to make the time bouncing off the rev limiter negligible.

So all the graph is intended to show is that at each instant in time (we'll use the acceleration side of the graph for discussion purposes right now) The Lightweight Pulley is at a higher RPM value than the stock pulley EXCEPT for idle, and redline, as you would expect. So again, the trendline used is a 2 period moving average, and was chosen ONLY to show a more smooth dataset as the actual datapoints can be hard to understand unless you know what you're looking for (which is rpm values at a given time). It is really hard to argue that the chart doesn't start at idle, and end at redline for both sets of data (no offset there), and that our pulley is always ahead of the stock pulley.

We do both agree though that small changes in weight on the rotating assembly can make a difference. All we're doing here is showing the data that we recorded, showing a change. Sure shedding weight from the timing chain or changing the pressure plate bolts will have an effect too, and people can always pick and choose what they want to do. Me personally, I would probably do the substantially easier thing and just change the crank pulley if I were looking to shed weight.

But also, it does look pretty cool, and that's one of the main reasons I'd put it on my motor too No need to apologize when your questions and points are perfectly valid. We're simply presenting the data that we observed consistently and averaged. Speculation is fun, but testing is even more fun. So thank you!

Chase
Engineering

[stugray]

Maybe if I saw the raw dataset I could be convinced.
However I look at the graph (the thin lines or the Moving averages) the time rate of change (the slope) appears to be the same for both datasets.
The moving averages seem to amplify this statement.
The slopes of the averages are the same.
Even the slopes of the thin lines appear to be identical with few exceptions.

Even if you argue they are different, they are not "different enough" for a statistically significant difference.

I would be interested for someone to actually calculate the rotational inertia of the various engine components.
Coming up with a total number analytically would be very difficult.
I think I could argue that removing grams from the perimeter of the starter teeth on the FW would make a bigger difference than 4 lbs from the pulley.
Or grams from the alternator pulley since it spins at ~4-5 times the speed of the engine and the kinetic energy is proportional to the SQUARE of the rotation speed.

So if the alt pulley rotates at 4X the crank speed, then a change in mass of the alt pulley would be 16X more effective than the same mass change in the drive pulley.
(of course I am guessing at the drive multiplier)

[cjd]

The slopes do start at a common 0,~700 and are different off idle, and in the transition into deceleration, both places I'd expect lower rotational mass to show up in such a log. Beyond that I have to agree, the rate of change is too similar for analysis by eye on a web optimized graph. The net idle to redline to... Approaching idle still gains time, so this will benefit people that like to rev their favourite tune, too!

All kidding aside, if you are chasing every last bit of potential rotational energy, this should help.

Sampling rate over the 12Hz offered by the OFT may be needed. (I think that's the right rate...)

[Calum]

Originally Posted by stugray

Maybe if I saw the raw dataset I could be convinced.
However I look at the graph (the thin lines or the Moving averages) the time rate of change (the slope) appears to be the same for both datasets.
The moving averages seem to amplify this statement.
The slopes of the averages are the same.
Even the slopes of the thin lines appear to be identical with few exceptions.

Even if you argue they are different, they are not "different enough" for a statistically significant difference.

I would be interested for someone to actually calculate the rotational inertia of the various engine components.
Coming up with a total number analytically would be very difficult.
I think I could argue that removing grams from the perimeter of the starter teeth on the FW would make a bigger difference than 4 lbs from the pulley.
Or grams from the alternator pulley since it spins at ~4-5 times the speed of the engine and the kinetic energy is proportional to the SQUARE of the rotation speed.

So if the alt pulley rotates at 4X the crank speed, then a change in mass of the alt pulley would be 16X more effective than the same mass change in the drive pulley.
(of course I am guessing at the drive multiplier)

Don't forget oil viscosity changes due to temperature, both in the engine and transmission.

[mike the snake]

What are your thoughts on the warnings and reports of failures from lightening both ends of the engine? I've gathered it seems OK to lighten one, or the other, but not both, something to do with harmonics and pounding bearings.

I ask because most people looking to lose weight are likely to get both lightened flywheel And lightened pulleys, and I' won'der if they might be setting themselves up for possible premature wear/failures.

I don't know how much actual proof there is to these claims, but I know a lightened flywheel makes a MUCH bigger difference in rotational mass, throttle response, so much so that the lightened pulley improvements are negligable in comparison.

[Travisty75]

Originally Posted by mike the snake

What are your thoughts on the warnings and reports of failures from lightening both ends of the engine? I've gathered it seems OK to lighten one, or the other, but not both, something to do with harmonics and pounding bearings.

I ask because most people looking to lose weight are likely to get both lightened flywheel And lightened pulleys, and I' won'der if they might be setting themselves up for possible premature wear/failures.

I don't know how much actual proof there is to these claims, but I know a lightened flywheel makes a MUCH bigger difference in rotational mass, throttle response, so much so that the lightened pulley improvements are negligable in comparison.

In the Subaru world we've been dealing with people throwing LWCP (lightweight crank pulley) and lightened flywheels on the EJ engines for a while. With those motors and both of those components lighter than factory, we've always introduced false knock.

It's a community-accepted fact that one or the other is okay, but not both. Most people opt to throw on a LWCP since it's so much easier to get to, but also because driving with a lightened flywheel is more tricky on the street, where 90% of people spend 100% of their time.

[weederr33]

Are you guys going to come out with a 5 piece pulley set like Raceseng's S2 kit?

[GrimmSpeed]

Originally Posted by cjd

The slopes do start at a common 0,~700 and are different off idle, and in the transition into deceleration, both places I'd expect lower rotational mass to show up in such a log. Beyond that I have to agree, the rate of change is too similar for analysis by eye on a web optimized graph. The net idle to redline to... Approaching idle still gains time, so this will benefit people that like to rev their favourite tune, too!

All kidding aside, if you are chasing every last bit of potential rotational energy, this should help.

Sampling rate over the 12Hz offered by the OFT may be needed. (I think that's the right rate...)

Exactly, the largest changes are measurable are off idle, and the transition to deceleration, as you would expect. Just getting down to basics: Tau = I*alpha, and nearly everywhere else you would expect the rate of change of the graph to be similar because the overpowering figure by a long shot is the torque. The point where the torque figure is smallest will be immediately off idle or off the pedal at any point, which is why the change is felt most in transition. We are definitely not saying it is as big of a change as a lightweight flywheel, and we certainly are not dynoing it and saying it made 13whp if you can remember anyone ever doing that :P Lots of people sell lightweight flywheels, but I've never seen anyone show any data to backup ANY claims. We did some testing, observed data that matches our hypothesis using that simple law that everyone knows (basically the angular version of F=MA), and thought it would be cool to show it.

I know you're kidding too, but I would kill to have a substantially greater sampling rate for logging.

Originally Posted by mike the snake

What are your thoughts on the warnings and reports of failures from lightening both ends of the engine? I've gathered it seems OK to lighten one, or the other, but not both, something to do with harmonics and pounding bearings.

I ask because most people looking to lose weight are likely to get both lightened flywheel And lightened pulleys, and I' won'der if they might be setting themselves up for possible premature wear/failures.

I don't know how much actual proof there is to these claims, but I know a lightened flywheel makes a MUCH bigger difference in rotational mass, throttle response, so much so that the lightened pulley improvements are negligable in comparison.

Originally Posted by Travisty75

In the Subaru world we've been dealing with people throwing LWCP (lightweight crank pulley) and lightened flywheels on the EJ engines for a while. With those motors and both of those components lighter than factory, we've always introduced false knock.

It's a community-accepted fact that one or the other is okay, but not both. Most people opt to throw on a LWCP since it's so much easier to get to, but also because driving with a lightened flywheel is more tricky on the street, where 90% of people spend 100% of their time.

Could not have said it better myself. In fact, that false knock is the main reason you don't see extremely light crank pulleys, because there is only so far you can go before you have that problem. On the FA20, that isn't an issue, and you can make the pulley quite light. Some of these other LWCPs end up being under a pound even.

At the end of the day I will always listen to the engine builders who have experience. If they're saying that a LWFW and LWCP are causing bearing wear issues I have no reason to believe they're lying, because what do they have to gain from that? Less engine rebuilds? :P Do I have the same first hand experience as these engine builders who have tore apart tons of motors and seen these exact issues? Nope, so I will listen to one who I trust.

And like I said, Travisty75's last paragraph sums it up perfectly. Good on ya

Originally Posted by weederr33

Are you guys going to come out with a 5 piece pulley set like Raceseng's S2 kit?

Currently we have no plans to do that, but you never know. We might add a few more bits to our lineups as time goes on, but right now we're working on some bigger projects

Chase
Engineering

[stugray]

Originally Posted by GrimmSpeed

I know you're kidding too, but I would kill to have a substantially greater sampling rate for logging.

I could loan you a tactrix.

I still believe that if you see or feel a 1% difference in the engine due to a pulley swap, then the new pulley has a 1% different drive ratio.

How much would the radius of a pulley need to differ from stock to underdrive the system by 1%? (Answer - not perceptible with the naked eye).

So IF I were to design a pulley such that the owner could "feel" a difference.... I would design the pulley to underdrive the system enough to see on a dyno, but the driven systems would not know the difference.
(Wink Wink.... Nudge Nudge)

[Mechazawa]

Regardless of how effective the mod is, I am pretty sure grimspeed is the first vendor on here to bother publishing (possibly even to bother calculating) moment of inertia. I think they deserve some credit for that.

GrimmSpeed I appreciate you not talking down to us.

Side note: The sprintex 335 (or whatever) folks need an undersized crank pully.