Aluminum pulley not a damper, thats ok with alotta folk?

[gmookher]

I have read thread after thread debating if the OE pully is a damper or not
read this

http://www.bhjdynamics.com/downloads...amper_Info.pdf

I dont want to get lost in semantics, damper=harmonic balancer, whateva

Its clear the factory crank is a "tuned rubber damper" after read this, amongst other PDFs

what SOA or your tech or the vendor has told you doesnt add up after reading the above.

also see for reference, below
I understand many have been sold and used and are still in use, but there is just too much science supporting its function be left intact unless youre planning on rebuilding the motor and pushing it really hard, looking for fastest time at the expense of durability. atleast thats what I walked away with - ymmv

http://www.pro-race.com/faq.htm

http://en.wikipedia.org/wiki/Torsional_vibration

http://www.eng-tips.com/viewthread.cfm?qid=260497

http://damperdudenz.tripod.com/id3.html

http://www.deviantmethods.com/bigmoo...rankdamper.pdf

http://www.atiracing.com/products/da...mper_dinan.htm

THE DANGERS OF POWER PULLEYS AND UNDERSTANDING THE HARMONIC DAMPER

by: Steve Dinan
I have been threatening for a long time to write a series of technical articles to educate consumers and to dispel misconceptions that exist about automotive after-market technology. Motivated by problems with customer's cars resulting from the installation of power pulleys, I wish to explain the potential dangers of these products and address the damage they cause to engines. The theory behind the power pulley is that a reduction in the speed of the accessory drive will minimize the parasitic losses that rob power from the engine. Parasitic power losses are a result of the energy that the engine uses to turn accessory components such as the alternator and water pump, instead of producing power for acceleration. In an attempt to minimize this energy loss, many companies claim to produce additional power by removing the harmonic damper and replacing it with a lightweight assembly. While a small power gain can be realized, there are a significant number of potential problems associated with this modification, some that are small and one which is particularly large and damaging! The popular method for making power pulleys on E36 engines is by removing the harmonic damper and replacing it with a lightweight alloy assembly. This is a very dangerous product because this damper is essential to the longevity of an engine. The substitution of this part often results in severe engine damage. It is also important to understand that while the engine in a BMW is designed by a team of qualified engineers, these power pulleys are created and installed by people who do not understand some very important principles of physics. I would first like to give a brief explanation of these principles which are critical to the proper operation of an engine. 1) Elastic Deformation Though it is common belief that large steel parts such as crankshafts are rigid and inflexible, this is not true. When a force acts on a crank it bends, flexes and twists just as a rubber band would. While this movement is often very small, it can have a significant impact on how an engine functions. 2) Natural Frequency All objects have a natural frequency that they resonate (vibrate) at when struck with a hammer. An everyday example of this is a tuning fork. The sound that a particular fork makes is directly related to the frequency that it is vibrating at. This is its "natural frequency," that is dictated by the size, shape and material of the instrument. Just like a tuning fork, a crankshaft has a natural frequency that it vibrates at when struck. An important aspect of this principle is that when an object is exposed to a heavily amplified order of its own natural frequency, it will begin to resonate with increasing vigor until it vibrates itself to pieces (fatigue failure). 3) Fatigue Failure Fatigue failure is when a material, metal in this case, breaks from repeated twisting or bending. A paper clip makes a great example. Take a paper clip and flex it back and forth 90° or so. After about 10 oscillations the paper clip will break of fatigue failure. The explanation of the destructive nature of power pulleys begins with the two basic balance and vibration modes in an internal combustion engine. It is of great importance that these modes are understood as being separate and distinct. 1) The vibration of the engine and its rigid components caused by the imbalance of the rotating and reciprocating parts. This is why we have counterweights on the crankshaft to offset the mass of the piston and rod as well as the reason for balancing the components in the engine. 2) The vibration of the engine components due to their individual elastic deformations. These deformations are a result of the periodic combustion impulses that create torsional forces on the crankshaft and camshaft. These torques excite the shafts into sequential orders of vibration, and lateral oscillation. Engine vibration of this sort is counteracted by the harmonic damper and is the primary subject of this paper. Torsional Vibration (Natural Frequency) Every time a cylinder fires, the force twists the crankshaft. When the cylinder stops firing the force ceases to act and the crankshaft starts to return to the untwisted position. However, the crankshaft will overshoot and begin to twist in the opposite direction, and then back again. Though this back-and-forth twisting motion decays over a number of repetitions due to internal friction, the frequency of vibration remains unique to the particular crankshaft. This motion is complicated in the case of a crankshaft because the amplitude of the vibration varies along the shaft. The crankshaft will experience torsional vibrations of the greatest amplitude at the point furthest from the flywheel or load.

Simplified Flywheel and Crankshaft Assembly

Harmonic (sine wave) Torque Curves

Each time a cylinder fires, force is translated through the piston and the connecting rod to the crankshaft pin. This force is then applied tangentially to, and causes the rotation of the crankshaft.

The sequence of forces that the crankshaft is subjected to is commonly organized into variable tangential torque curves that in turn can be resolved into either a constant mean torque curve or an infinite number of sine wave torque curves. These curves, known as harmonics, follow orders that depend on the number of complete vibrations (cylinder pulses) per revolution. Accordingly, the tangential crankshaft torque is comprised of many harmonics of varying amplitudes and frequencies. This is where the name "harmonic damper" originates.

Critical RPM's

When the crankshaft is revolving at an RPM such that the torque frequency, or one of the harmonic sine wave frequencies coincides with the natural frequency of the shaft, resonance occurs. Thus, the crankshaft RPM at which this resonance occurs is known a critical speed. A modern automobile engine will commonly pass through multiple critical speeds over the range of its possible RPM's. These speeds are categorized into either major or minor critical RPM's.

Major and Minor Critical RPM’s

Major and minor critical RPM's are different due to the fact that some harmonics assist one another in producing large vibrations, whereas other harmonics cancel each other out. Hence, the important critical RPM’s have harmonics that build on one another to amplify the torsional motion of the crankshaft. These critical RPM’s are know as the "major criticals". Conversely, the "minor criticals" exist at RPM's that tend to cancel and damp the oscillations of the crankshaft.

If the RPM remains at or near one of the major criticals for any length of time, fatigue failure of the crankshaft is probable. Major critical RPM’s are dangerous, and either must be avoided or properly damped. Additionally, smaller but still serious problems can result from an undamped crankshaft. The oscillation of the crankshaft at a major critical speed will commonly sheer the front crank pulley and the flywheel from the crankshaft. I have witnessed front pulley hub keys being sheered, flywheels coming loose, and clutch covers coming apart. These failures have often required crankshaft and/or gearbox replacement.

Harmonic Dampers

Crankshaft failure can be prevented by mounting some form of vibration damper at the front end of the crankshaft that is capable of absorbing and dissipating the majority of the vibratory energy. Once absorbed by the damper the energy is released in the form of heat, making adequate cooling a necessity. This heat dissipation was visibly essential in Tom Milner's PTG racing M3 which channeled air from the brake ducts to the harmonic damper, in order to keep the damper at optimal operating temperatures. While there are various types of torsional vibration dampers, BMW engines are primarily designed with "tuned rubber" dampers.

It is also important to note that while the large springs of a dual mass flywheel absorb some of the torsional impulses conveyed to the crankshaft, they are not harmonic dampers, and are only responsible for a small reduction in vibration.

Cut-Out View of a Tuned Rubber Harmonic Damper

In addition to the crankshaft issue, other problems can result from slowing down the accessories below their designed speeds, particularly at idle. Slowing the alternator down can result in reduced charging of the battery, dimming of the lights, and computer malfunctions. Slowing of the water pump and fan can result in warm running, while slowing of the power steering can cause stiff steering at idle and groaning noises. It is possible to implement design corrections and avoid these scenarios, but this would require additional components and/or software.

Our motto at Dinan is "Performance without sacrifice". We feel our customers expect ultra high performance along with the legendary comfort and reliability of a standard BMW.

While it is common that a Dinan BMW is the fastest BMW you can buy, performance is not our only goal. Dinan isn't just trying to make the fastest car. Instead a host of considerations go into the development of our products. Dinan puts much more effort into these other areas than does our competition.

These considerations are Performance, Reliability (Warranty), Driveability, Emissions, Value, Fit and Finish. We feel that the power pulley is a bad way to get extra power from and engine and the potential for serious engine damage is too great.

This is a simplified explanation meant to be comprehensible by those who are not automotive engineers. In trying to simplify an extremely complex topic some precision was sacrificed although we believe this explanation to be as accurate as possible. We encourage our customers to educate themselves and understand the automotive after-market because we believe that our products are the best researched, engineered, and fabricated products available.

For those interested in a more in depth and technical explanation of this topic, the reference book is Advanced Engine Technology, written by Heinz Heisler MSc,BSc,FIMI,MIRTE,MCIT. Heinz Heisler is the Head of Transportation Studies at The College of North West London. His book is distributed in this country by the SAE (Society of Automotive Engineers).

[sho220]

Good stuff...thanks for posting. Aftermarket pulley's are not worth the risk in my opinion...although lots of people seem to run them with no issue.

[theredtape]

Very good info. Long story short, don't replace harmonic dampeners with lightweight pulleys. Automotive engineers spend a long time balancing the crank and designing tuned absorbers. It's not a good idea to unbalance it.

[kwood9000]

Haven't seen confirmation that the original pulley is balanced. There has been conjecture that it doesn't need to be since the boxer engine doesn't have the same kind of vibrations that other types of engines have.

[lam86]

FWIW I ran my old RS approx. 195k with unorthodox lightened/underdriven with no engine issues, until the headgaskets eventually let go at 180k that being said, there is no guarantee on your new engines.

[Embarrassed]

The real question is what are they damping? Certainly the wet noodle cranks from a I6 or odd fire V8 need all the help they can get. I have never seen a modern 5 bearing I4 engine that needed one. That said, almost every modern engine has them. It seems that it has more to do with belt life (they also reduce damping to the belts and accessories).

On a flat 4? No idea. I'm sure this has been discussed to death on WRX forums. What do they say? I mean, Dinan is a smart guy and all but he is a BMW inline 6 expert. I would think Cobb would be a better reference for the BRZ.

O

[gmookher]

Originally Posted by kwood9000

Haven't seen confirmation that the original pulley is balanced. There has been conjecture that it doesn't need to be since the boxer engine doesn't have the same kind of vibrations that other types of engines have.

OE pulley is cast iron, with a elastomeric damper method. You dont doubt that do u?

no. (and I dont mean this personally, k?)

so. read the links, and you will see the confirmation you need... again with semantics of balanced vs not. its not the pulley that is in balance, its the whole system. crank. pulley, crank, flywheel, the whole kaboodle.
I know perrin or agency has no data on torsional vibration characteristics that change. Its a piece of 6061 cnc'd down as light as they can get it without breaking or flexing to a point of fatigue. I'd sooner lighten a flywheel than a crank, its just different scales of change of weight

I dont doubt that a lightened flywheel has the same result on the way harmonics get transmitted, put into standing waves, and combine frequencies that accelerate fatigue.
I also do not doubt that taking all this weight of can make you faster.

why prove or disprove if the pulley is a balanced or not? the education I shared was for your benefit, not to argue a point, theres nothing moot here. lighter is faster.

If you took the time to read the link, you would know that that opposite (180 degrees) the cranks other counterweight, the flywheel, is where the angular torsional nvh ends up that they have countered--> there is a reason the engineers put a disc weigh x.xx lbs there. but you dont have to agree with me or the links posted. I am glad that if I ever choose to, there are many folk who have run pulleys, and flywheels with no issue

I do not doubt ther are many happy folks running lightweight pulleys. I really want to buy one, but I cant make a physics case for it; and there are many engineering reasons its mod I will not be doing. Just sharing so you can make an educated choice too.

[kwood9000]

Originally Posted by gmookher

OE pulley is cast iron, with a elastomeric damper method. You dont doubt that do u?

no. (and I dont mean this personally, k?)

so. read the links, and you will see the confirmation you need... again with semantics of balanced vs not. its not the pulley that is in balance, its the whole system. crank. pulley, crank, flywheel, the whole kaboodle.
I know perrin or agency has no data on torsional vibration characteristics that change. Its a piece of 6061 cnc'd down as light as they can get it without breaking or flexing to a point of fatigue. I'd sooner lighten a flywheel than a crank, its just different scales of change of weight

I dont doubt that a lightened flywheel has the same result on the way harmonics get transmitted, put into standing waves, and combine frequencies that accelerate fatigue.
I also do not doubt that taking all this weight of can make you faster.

why prove or disprove if the pulley is a balanced or not? the education I shared was for your benefit, not to argue a point, theres nothing moot here. lighter is faster.

If you took the time to read the link, you would know that that opposite (180 degrees) the cranks other counterweight, the flywheel, is where the angular torsional nvh ends up that they have countered--> there is a reason the engineers put a disc weigh x.xx lbs there. but you dont have to agree with me or the links posted. I am glad that if I ever choose to, there are many folk who have run pulleys, and flywheels with no issue

I do not doubt ther are many happy folks running lightweight pulleys. I really want to buy one, but I cant make a physics case for it; and there are many engineering reasons its mod I will not be doing. Just sharing so you can make an educated choice too.

Not arguing, just not educated well enough in this area.

Yes, it appears that changing the weight of the pulley will impact the "balance" of the system. How much and to what extend is the big unknown. Perhaps the system is over-engineered to handle such additional forces, so maybe the impact will be marginal.

[jadewbj]

I was never a big fan of these, this helps me feel better about not getting one.

I would like to hear a counter argument from the makers or someone else with more knowledge than I on the matter.

I like to learn new things.

[SkullWorks]

That article, was written specifically in regards to the I6 motor which has a real problem with Major critical RPM

As far as the critical RPM's go, such a thing is dependent on the length of the assembly, as much as if not more than any other factor. The harmonics of the crankshaft and therefor it's "natural frequency" are, as stated dependent on size shape and material, you will find that the H4 has much more mass per linear inch than the BMW I6 crankshafts that were the focus of the Dinan Rep's statements quoted above. Not to mention the overall length is significantly shorter. (2 cylinders long vs 6 cylinders long.)

While a I6 is a very "balanced" engine the H4 design has opposed cylinders making it again more balanced.

I'm not here trying to state that engine dampers are pointless, I will happily point out that this motor (FA20) is not subject to violent "major Critical RPM's" until a significantly higher RPM that we will see for street or track usage until people start winding these things like street bikes...which in my experience, don't have dampers... at least my 618cc Ducati doesn't have one

[xwd]

Do a search on NASIOC you will find plenty of info.

What you won't find is a single engine failure due to a lightened pulley. I used one on a 300+ WHP WRX with a 7500 RPM redline for almost 100K miles.

In conjunction with a lightened flywheel you will find some people with misfire issues, time will tell if the same happens to the FA20.

[gmookher]

Originally Posted by dwx

Do a search on NASIOC you will find plenty of info.

What you won't find is a single engine failure due to a lightened pulley. I used one on a 300+ WHP WRX with a 7500 RPM redline for almost 100K miles.

In conjunction with a lightened flywheel you will find some people with misfire issues, time will tell if the same happens to the FA20.

Agreed.
Good to know the engineers are over thinking this

This is very good to know

[theredtape]

Originally Posted by SkullWorks

While a I6 is a very "balanced" engine the H4 design has opposed cylinders making it again more balanced.

The straight six is also a "perfectly balanced engine" by design.

Reguardless of engine balance all objects have natural frequencies. If there is rubber on the stock pulley then it is meant to absorb the vibrations at probabaly the first two natural frequencies. I'm not an expert on modal testing but I do know that someone at Subaru put some sort of thought into it.

Now I did a lot of research and it seems lots of people do run the pulleys without problems. So I am not trying to say that it's gonna kill anyone's engine or that anyone is dumb for using a lighter pulley. I'm just saying that if the stock one has a damping effect then it's probabaly for a reason.

Everyone owns their cars. Do whatever you please with it.

[Im_SPEED]

Thanks for all tue info i was kinds thinking the same things lightwieghr non dampered crank pully will blow the oil pump to bits on a 7th gen celica but it has a 8200 redline and i have read h4 are way more balanced out of the box. I think i will wait.