Lightened Crank Pulley

[Brad850]

Me and a few members were recently talking about the lightened ARD crank pulley, and someone mentioned that a lighter pulley will raise RPM at any given speed. Is there any truth to this? 

For example my one gripe with the m56hk is the very high rpm while cruising on the highway. Sitting at 3k at 70mph always has me looking for an extra gear. Does my ard pulley really have anything to do with that?

[Tommy.]

Mine is the same way. And I do not have a lightened pulley.

I know there were two different m56 (m56H, m56L) I believe the L had taller gears thus letting it cruise at a lower RPM. If I am not correct on the gearing forgive me but that's what I remember reading.

[S70-R]

The crank pulley, no matter how light it is, has nothing to do with gearing and thus nothing to do with RPM being higher or lower. It can however help the engine to rev easier.

Crank pulley is just an harmonic/counterweight pulley and is also used for the accessories belt. Gear box ratio and differential ratio are the only things that determine your RPM at a given speed.

[Brad850]

2 hours ago, Tommy. said:

I know there were two different m56 (m56H, m56L) I believe the L had taller gears thus letting it cruise at a lower RPM. If I am not correct on the gearing forgive me but that's what I remember reading.

You're correct Tommy

Thanks for the info S70-r. That confirms what I was thinking. Although, the more I read about this topic, the more I feel like I should revert back to stock.

[S70-R]

Probably yes.

From my readings and understanding, personally I'm not a big fan of lightened crank pulleys or lightened flywheels without taking into account all the other inertia componentes of the engine, especially the crankshaft.

An engine, especially its crankshaft (along with rods and pistons) is designed to work properly with a certain crank pulley weight and a certain flywheel weight. Changing the weights of these 2 may create balancing/inertia/dynamic problems in the engine.

If we take into account all the inertia mass when the clutch is engaged, we are talking about the engine inertia mass plus the clutch mass, the gear box mass, the diff. mass, the axles mass and wheel/hub/rotors etc mass.

So, a lightened pulley will represent only a very very small percentage of all this weight/mass. Even a lightened flywheel will represent a small percentage over the total inertia mass.

I prefer to stick with a stock and factory balanced set of crankshaft, pulley and flywheel once the potential gains are very small when the clutch is engaged and once messing up with the weights and balance of the engine can have nasty consequences.

I can be wrong though. This is my current view and opinion on this matter.

[dougy]

 

Modern engines are internally balanced and this process has improved even further since the 90s. 

 

if anyone want to sell me their billet crank pulley , let me know cause i need one for my c70...my 850 has it for 40k

[Kit Vexed]

im with dougy, any of you guys want to give up your ARD/lightened crank pulleys i'll take em..

 

i've been running an unorthodox crank pulley for 9 years now with 0 problems..

 

if you guys believe your engines are not going to last as long or blow up from light weight rotational components that's fine lol

i aint never heard of a car suffering from taking off weight from balancing components as the lighter components replacing them are balanced  =)

 

i like revving quicker and slowing faster...  manufacturers keep these components heavier more for driveability than reliability..  

reliability aint got nothing to do with a lighter flywheel.. there was just the single mass thread talking about the increase engine noise from this flywheel because it is LIGHTER than the dual mass..  ergo car manufacturers know ppl are going to freak if they hear a brand new car making all this noise..  and people dont want the car decelerating or 'bucking down' so quickly when you let your foot off the throttle as is the nature of lighter rotational components..

they're heavier for comfort/driveablity, NOT BECAUSE LIGHTER COMPONENTS ARE BAD.

[S70-R]

I'm aware that the heavier flywheels give more road driveability when shifting and when accelerating from 0.

However, by what you guys are saying, it seems that weights on the engines don't matter at all.

I don't share that view at 100%. I'm not saying that light is always BAD. I'm saying that an engine that was designed to work with certain weights may not like different weights on the long run.

We shouldn't also forget that the crank pulley is not just a counterweight. It is meant to absorv vibrations/harmonics. If the crank pulley doesn't do its job properly, in the long run you may end up with a damaged crankshaft for instance.

And once again, when you put a lighter pulley or flywheel you will for sure feel the car accelerating easier when the clutch is disengaged.

However, when the clutch is engaged, the easier acceleration would be much less noticable because the rotating mass increases a lot.

And because of that (little gains to be add), I prefer to not mess up with the engine balances. I'm not saying you will for sure f*** the engine. I'm just saying what I prefer given the small gains to be added.

[turbobrick]

I would be hesitant, they phrase it that it still provides dampening, i'm guessing they're talking about a harmonic balancer.. don't see how ??  I would say it's not worth it... I did have pulleys on my M3, the crankshaft pulley however was not replaced, just the underdrive system.

[survolvo]

I would like to know how many pulleys Lucky sold, and how many people had driveshaft issues. I bet not even a percentage, if any of the customers.

With that said, I know there was talk about people having problems with the belts walking off the pulley; I never heard it from the horses mouth or seen it happen, its always "I have a friend whose cousins aunts brothers nephew had the belt walk off."

Too much hearsay and theories, not enough evidence or facts to back up all the naysayers. IMO

[S70-R]

The possible issues are not likely to be seen during the first 40 / 50 or 60k miles. It would be in the longer run probably.

Anyway, you said "not even a percentagen, if any of the customers".

And did you already calculate what is the percentage of the rotational weight loss? It's almost 0...

It's almost like hoping that reducing a few lb/kg from the car will do any big difference.

Once again, my point is: Given the really small (if any) gains I wouldn't bother with a light pulley.

Don't we wonder why volvo didn't go with a lighter pulley?

[dougy]

ok...lightweight crank pulleys been around for 20 years now, about... right? will be conservative and say at least 10,000 of them sold out there world wide on many different car models...ok...since you are searching and reading and believing every article out there and lets assume you/they are correct... light weight crank pulleys must be doing some serious damage out there...can you find me handful of articles on any car that had one on showing/pics the damage it has done?  any car forum  ...

make sure the cars are not from 50, 60, 70, 80

[Commander Riker]

I have a VIVA single mass flywheel.  It dropped 9lbs from my previous dual mass setup.  So far... I love it!   Would get a lightened crank pulley if possible too.  

[dougy]

surely we will have some very upset car owners showing pic and telling what it has done to their car...i cant wait to see all the threads out there...cause i know if my engine would fail do to having one i would post it up ...

[S70-R]

23 minutes ago, dougy said:

ok...lightweight crank pulleys been around for 20 years now, about... right? will be conservative and say at least 10,000 of them sold out there world wide on many different car models...ok...since you are searching and reading and believing every article out there and lets assume you/they are correct... light weight crank pulleys must be doing some serious damage out there...can you find me handful of articles on any car that had one on showing/pics the damage it has done?  any car forum  ...

make sure the cars are not from 50, 60, 70, 80

Well, for sure that if you search for it you'll find.

And I don't blindy "believe" articles or posts. I make my own judgement.

Anyway, try focusing on my main point. Considering the really low gains (if any measureable gains are to be added) and considering that exists a remote possibility of something going wrong, should I even care about a light pulley?

Do you believe that taking a single 1 gallon from your gas tank will make you any real faster?

You would gain more by using ligher wheels than using a lighter crank pulley.

Don't forget that the engine does not pull only the crank pulley and flywheel. It pulls more than 1400kg!

That's the point...

But if you guys are happy with it simply keep using it. For me, personally, I see no point or any big advantage considering how much weight the engine has to pull.