Crank Pulley - How do they work?
 

I recently talked to a fellow FRS owner and he mentioned that he had his crank pulley swapped to a lighter one. I was looking through the net and most people vaguely mention that it improves throttle response, less rotational mass etc. Sounds great but I'm still not sure how they work exactly. Forgive me as I'm new to this.

I'm very interested in getting one since they're rather cheap (and not too difficult to install) but I'd like to know in more detail how a good crank pulley will affect the FRS in general. Will appreciate any input especially from those who have swapped theirs and some recommendations regarding which one to get wouldn't hurt :thumbup:

Many thanks in advance!

I have lightweight crank pulley installed. Although I know many people on this forum reckon they are great I could not be sure if there was any difference after installation.

There's two potential effects. If it's lighter, the engine will rev more quickly as there's less inertia fighting it. Downside is poorer vibration damping.

If the diameter is made smaller, then the accessories are driven more slowly and consume less power - downside is potential issues with cooling (if the water pump is belt-driven) and charging/air conditioning.

Any engine has a specific peak output. That is, a certain amount of horsepower/torque that it is capable of producing. Everything attached to or run by the engine take a certain amount of that power away.

Think of it this way...you are riding an exercise bicycle with no resistance on it. It's pretty easy to pedal...takes almost no effort. However, once you start adding resistance, it becomes progressively more difficult (takes more effort/power) to keep pedaling at the same speed. It works the same way with an engine.

Every pulley on the engine is another source of resistance. In the same way it is easier to spin a pencil in your fingers than it is a steel rod, the more mass something has, the more difficult it is to spin.

The resistance of any physical object to a change in motion is referred to as "inertia" (p). The formula for inertia is p = (mass) * (velocity). As you can see, at a constant velocity (speed), something that has more mass (weight) will have more inertia than something that has less mass. Therefore, a heavier object is going to be more resistant to changing speed than a lighter object. This is the reason why sport bikes can accelerate almost as fast as supercars with just a fraction of the power.

This means that a heavier pulley will have more "parasitic drag" on the engine than a lighter pulley. Lighter pulleys reduce the inertia of the pulley system, which allows the engine to rev faster (better throttle response) and frees up a little of that HP lost due to parasitic drag.

Fun fact to round this all off - A Top Fuel engine's supercharger has a parasitic loss equivalent to around 600HP! That means you'd need 3+ FA20 engines just to turn the supercharger at speed!

there is so much debate about crank pulleys, but the way i see it the crank pulley is lighter there for less mass for the engine to turn and less parasitic power loss. pretty much cut and dry. i look at it as dropping weight, no one part you remove from your car is going to be noticeably faster, but things add up, and every little bit helps.

edit: captain slow types faster than me i guess, lol.

This is only true for linear motion. Angular momentum is expressed as moment of inertia x angular velocity.

I've heard these pulleys causing issues and possible damage. Anyone care to elaborate?

That's a fantastic explanation, Cap'n. THANKS! Really appreciate it.

Anyone who's installed a lightweight pulley felt any differences so far? Or any issues which pop up? Curious to know.

Just wanted to make it as simple as I could for this case :)

I agree with everything you said but this.

I have had my Honda CBR600RR cross the 1/4 mile at 10.9 seconds at 132mph. With a pro rider and my bike stock, it could do 0-60 in 2.7 seconds and the 1/4 mile in 10.6 seconds.

This is faster than the majority of super cars.

with that said; my bike tops out at 170 mph, where as super cars usually top out aroung 200 mph


BUUUUUT this is way off toipic of the thread

so which crank pulley are you guys going with that seem to actually have a better performance after the swap??

Some people have had damage due to installation issues, as there's a crankshaft spacer that sits between the pulley and the crankshaft which can easily fall out and is incredibly difficult to put back in if it does:

http://www.ft86club.com/forums/showthread.php?t=26386

However, if you're careful and hold the spacer in when you remove it, there's not much to worry about.

The loss of mass on the pulley means better throttle response and a tiny bit more power to the ground. It also means the engine has a little less intertia, which in some applications means a rough idle and the engine is easier to stall with a MT and street driving.

I think on the FA20 if you installed all the lightened pulleys and and a lightened flywheel, it might make daily driving a bit difficult and you might stall and look like a chump in front of the cutest girl in your high school.

Thanks for the info! But high school? LOL :respekt: I wanna meet the high school student who has a FRS.

After I took mine off I noticed the quicker throttle response missing, until then I didn't think it was making any difference.

@Ray_32 I've used bot the Perrin and Kartboy crank pulley. The Perrin pulley comes with directions that will lead you to over tighten the bolt if you follow them. If you get that one, DO NOT follow the directions, just torque it to the specified amount. The Kartboy pulley is good, but a few of us have had issues with a whining noise from it. Apparently a different belt will take care of it. I hasn't bugged me enough to bother fixing it.

There are better ways to spend your money. I installed lightweight pulleys on my last car, there was no perceivable improvement.

My personal experience is that it is not worth the money, and potential headaches that could arise.

That will only happen if you install it wrong.
http://forums.nasioc.com/forums/showthread.php?t=444518

I didn't notice much improvement in acceleration with the GFB lightweight pulley set. Only thing I noticed was that the car's rpms drop more quickly. A lightweight flywheel, driveshaft, or wheels will yield a more noticeable difference in acceleration, but those are all much more expensive haha.

How do they work?

They go round and round. Put a belt around it, and it causes other pulleys to go round and round, which then power other things.

The more you know.

The effect a light weight crank pulley has on actual acceleration is negligible at best. On my last car though the difference in how fast the tach climbed was night and day. Enough so that I had to relearn how to launch in normal traffic.

This car seems to have a lot more mass in the rotational assembly because the difference in feel isn't that big. But it does feel sportier with the revs climbing and falling faster. This is the only real reason to put on a light weight crank pulley. If you're looking for a part to make your car faster, look somewhere else. If you want to enhance the overall driving experience this is a cheap place to start.

Ha I have a lightweight crank pulley and flywheel, goin to be installing a 12lb driveshaft soon...should be nuts to feel with my turbo haha

On a serious note: These do have a decent effect.

Its not straight line racing, although it does help. Its the response where you get the gain. Canyon/track battling, throttle balancing, on/off throttle action, everytime the car reponds quicker. Thats where the improvement lies IMO

Light crank pulley + flywheel + open exahust + intake/induction noise + on/off throttle driving action = win.

I agree. i have had light weight pulleys on two of my vehicles..both were night and day. When i had the perrin pulley on my frs it felt no different
than stock. i was pretty disappointed. the only thing i noticed was that my tach dropped faster than usual but nothing too crazy. Spend your money on something else

I'd love to, but I'll probably be ignored. Let's give it a whirl anyway.

OEM crankshaft pulleys are not simply pulleys. They are also harmonic dampers. Do not confuse harmonic damper with harmonic balancer: they're two totally different things.

A harmonic damper acts like a rotational version of a shock absorber in your suspension. A damper is used to control the motion of a spring. In reality, everything is a spring to one degree or another: including the crankshaft. It's just a really, really stiff spring. But, instead of being like a coil spring in your suspension, it's more like a sway bar since it twists as a force is applied to it (like when a piston is being forced down during the power stroke).

So what, the crankshaft twists a little on every power stroke. Big deal right? Well, yes, it can be a big deal.

Most objects have a natural frequency. In other words, when vibrated at that frequency, they begin to self excite until they break apart and stop vibrating. You know when TV dramatizes opera singers causing glasses to shatter? That is a well known example of natural frequency. The crystal (it doesn't actually work with glass) is vibrating at its natural frequency and as the opera singer holds the note, the crystal continues to vibrate harder and harder until it breaks.

A crankshaft also has a natural frequency. Now, chances are slim to none that you will hold the correct rpm (frequency) long enough to get it to vibrate at its natural frequency and shatter, but it will deflect much more than it normally would at that frequency.

That's where the harmonic damper comes into play. The OEM crankshaft pulley has a rubber portion that is tuned to cancel out the natural frequency of the crankshaft as well as absorb vibrations associated with the winding and unwinding of the crankshaft as it deflects slightly on each power stroke.

While it is true that there are tons of people that have run lightweight crankshaft pulleys with no ill effect, there exists a risk that engine damage can occur when the harmonic damper is eliminated. Now, if the FA20 is like other boxers, the oil pump is driven off the nose of the crankshaft. Excessive movement from un-damped crankshaft oscillation could cause damage to the oil pump and possibly other components over time (not to mention that aluminum pulleys on steel crankshafts can gall along with other issues).

Keep in mind that companies like Fluidamper and ATI exist for a reason. Not only are they aware of the significance of harmonic damping, but they have the equipment and knowledge to develop crankshaft pulleys that have appropriate damping characteristics for each specific engine.

The bottom line is that the almost inconsequential improvement in throttle response is not worth the risk associated with running an engine without it's harmonic damper.

Wow guys, thanks for the info! I think I've made my decision - will stay away from the crank pulleys for the time being and wait out the warranty (2.5 years to go!) before I actually have a go. Will look into other parts for now. Cheers.

You heard this "WHERE"?

I consider myself a forum whore to say least, I creep this forum nightly for a few hours b4 bed and haven't even heard of a single issue other then install issues that were proven to be USER error, not a single (-) on what any of the varieties of pulleys have done.
Is there a thread or post on failures...? If someone can point me to one I'd like to see it, if it exists???? :iono::iono::iono::iono:

CAN I REPLACE THE CRANK PULLEY HARMONIC BALANCER? The harmonic balancer has the sole responsibility to retard or lessen the resonant frequencies that occur during the normal operation of any internal combustion motor. The crank is like a tuning fork for musicians; when the firing cycle hits each cylinder, its like a flick to the tuning fork. So when you see the term "harmonic", it is a literal description of what is occurring to your crank. Your crank is actually flexible, believe it or not, if it wasn't, your engine wouldn't last more then 10,000 miles. It flexes on a microscopic level to absorb the explosion from each cylinder, this flex is precisely what creates an engine's natural frequency. Some vehicle's frequencies are more violent then others due to the architectural layout of the cylinders. For example, a V6 or V8 will have higher resonance because the downward thrust of each cylinder travels through the center-line of the crank in a non-linear pattern; this actually has the ability to amplify the frequency, depending on your RPM. Compare this to an I6 or I4 and you reduce the harmonics due to the linear pulse of the cylinders approach the crank from a single direction. Finally the Flat-4, with force traveling through the crank to opposing cylinders, the frequency is reduced by its own operation. We're not saying that the frequency is completely eliminated! We're saying that of all the engine formats available, a flat-4 is the best candidate for a lightened crank pulley.

Good stuff mate, but bear in mind this is a flat 4 not a v6 or v8...plus we're in 2013 not in the 80 when indeed some of the big engined cars needed a harmonic damper.

Maybe people from raceseg might be able to help you! @Raceseng

There was a thread awhile ago when the Perrin pulley first hit the market. But since then I'm pretty sure it's been chalked up to user error having to do with the seal.

Word on the street is the fa20 is extremely well balanced and didn't even have a balance fire the crank pulley. So with proper install and a fine machined product the increased wear would only come from a faster rev, which is what the lighter pulley is supposed to do. Imo.

55k km on my LCP, no issues to report.

- AdrianG

Only 620 days since previous post.
Awesome necro on a subject that has been done to death.

Reporter: Excuse me madam, have you heard about the FA20 balance?
Grandma: Oh yes sonny. When I was going down on Frederick, my beloved hubby of over 60 years, he was moaning uahh uahh the FA20 balance, the balance, ahhh uahhh. I knew then that balance of the engine was very good and didn't require any special sauce.
Reporter: There you have it folks. The word on the street. David Mathews reporting for RaceCar Engineering.

All that time wasted with modal analysis. I could have just done a word-on-the-street study.

David Mathews:Sir! Sir! Excuse me sir, would you care to comment of the balance of the FA20 engine?
Gentleman: Bah! It's hopeless!
DM: Hopeless sir? But word on the street is that it's very good.
Gentleman: That maybe so but when I attach a prostate tickler there is hardly a tremor to be felt. I speak from experience. A Harley V twin is much more enjoyable.
DM: Mmmmm... we've heard conflicting stories. I wonder if we can speak to some one else?

David Mathews: I have spoken to a number of people who wished to remain anonymous but there were few people who were willing to publicly comment on what the word on the street was. It was suggested I have a look over yonder only to discover this.
Attachment 109170

David Mathews reporting for RaceCar Engineering.