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Super Moderator!!ON PATROL ALL OVER!!
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BY STEVE DINAN OF DINAN BMW


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.





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.
 

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Super Moderator!!ON PATROL ALL OVER!!
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Discussion Starter · #2 ·
part 2



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.

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).

http://www.atiperformanceproducts.com/products/dampers/damper_dinan.htm
 

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going broke fast
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in-dept right up.power pulley's have there place in the domestic world where the crank pulley bolt's to the harmonic balancer.just looking at our crank pulley with the two peice and rubber ring pretty much let me know it was needed.
that said.opinion's on ati superdamper or fluidamper.
 

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in-dept right up.power pulley's have there place in the domestic world where the crank pulley bolt's to the harmonic balancer.just looking at our crank pulley with the two peice and rubber ring pretty much let me know it was needed.
that said.opinion's on ati superdamper or fluidamper.
+

both ATI and Fluidamper are high quality.

ATI has the capacity to custom make a damped crank pulley for ANY motor application. Fluidamper does not do custom crank pulleys to my knowledge but that might have changed.
 

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i have taken plenty of vibrations classes and the theory behind this write up makes perfect sense for a completely stock motor.

if we are discussing a racing engine or a pure performance engine that barely sees any road use then this is of no use. on racing engine it is all about the best and most of everything. as little weight, as much acceleration, and grip. we all know that jazz. the thing is that most racing engines do not utilize a damper because it is extra weight. if the engine is being prepped for racing every component is balanced to ensure most consistent performance.

when i built racing engines at my shop and start with a factory part like the crank you would be amazed how crappy the balancing on them is. im not just talking about one particular motor. have done everything from bmw m42 and m40 motors, to toyota atlantic 4age, pretty much every combination of VW 4 cylinder engines, as well as a few random hondas, opel, and saab motors.

the stock crank balance is crap. when you balance the crank down to about .1g. the rods, and pistons as well the issues of damage to bearings and seals is greatly reduced.

for street car keep the damper. for a racing engine you can ditch it.

what most people have on these forums are weekend performance cars and not "race cars" as some people want to refer to them.
 
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Suprastar
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Wow! I learned a crap ton off of this read. This lets me know I still have plenty to learn still but its a great start. Im going to order that book also. Thanks Ranger for the extremely valuable info.
 

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:bs: Steve Dinan doesn't know what he's talking about. There is a response to Steve's non-sense on the UR site and also check out the UR FAQ section and the Blog link on the main page. 14+ years of real world facts not conjecture from arm chair engineers in a vacuum.

Just a simple fact from my response to Steve: If the stock BMW crank pulley was an engine protection damper then by increasing power the way Steve does with his supercharger the damper would no longer be adequate and therefore his entire theory it busted!

Its time to start sourcing the real reason for engine problems and not blaming the easiest thing with no facts. I've run my 1993 MKIV TT for well over 30K miles, countless other Supra's from mild mannered street Supras to Vinny Ten to Passen Motosports Speedvision road race car from back in the day. The stock autos on these cars were the weak link, once a GM tranny is bolted on the problem stops.

I'm not going to get into it here cause I go over everything clearly and concisely in our FAQ and our Blog. As you'll read without the stock crank pulley being interference fit it cannot be an engine protection damper. All ATI and Fluidampr buyers spent money for nothing and added more weight to their crankshaft than the stock crank pulley. The best way to lose HP.

Shawn
 

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I've had Unorthodox crank pulley for over a year on my daily driver 98 APU 6-speed,no problems at all


After 3 days I finally got my crank bolt off. I got an Unorthodox crank pulley and wondered if I should use it. I should have an OEM pulley at my house in a few days and I haven't decided if I will use the Unorthodox pulley yet.

I have had 3 mustangs and I used underdrive pulleys on 2 of them with zero problems. In the Supra world people are quick to say DON"T USE IT!! it will ruin your engine. I haven't seen anyone say, I used an underdive pulley on my Supra and this is the damage it did. I have seen a few people say I used an underdrive pulley and I haven't had any problems. I didn't buy an ATI to replace my recently broke OEM pulley because it overdrives the system. Overdrive means maybe better power from the alternator and more coolant flow, but it would cause a power loss. I don't want to install a power loss device on my car. If the ATI pulley had the stock drive ratio I would have bought one.
 

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Been running our crank pulley, first underdrive and now the new stock diameter since 1999. I now make 650 at the crank and pull through 8000 RPM and the motor is going strong.

That being said I think a damper, of the same weight or lighter than the stock crank pulley would absorb frequencies and torsionals that are detrimental to total potential power output. The existing damper products are signifiantly heavier than stock and therefore are worse for the engine as they create a hammer effect as the extra mass is detrimental and exascerbates the forces on the rotating assembly.

We have been developing a damper for many years now, most of the delay was the 6 year battle we had with the US Patent Office. We now have the Patent in hand and are working on the final manufacturing processes for the elastomer right now. We hope to debut the Ultra Damper line later this year. The Ultra Damper will be OE weight or lighter in all cases.

Shawn
Unorthodox Racing
 

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Boost Junkie
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Basically, it's a terrible idea on a 2JZ. End of story.

Steve
 

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Basically, it's a terrible idea on a 2JZ. End of story.

Steve
Got that right.
A terrible idea on any straight 6 engine.

The small amount of rotational mass removed to add an underdrive, non dampening crank pulley is a very very bad idea.

I would bet that if the engine does not grenade itself, no one actually sees the damage it begins to cause. (unless its torn down for rebuild)
Main bearing and rod bearing abnormal / accelerated wear would be one of the top on the list of many.

The easiest way to explain what happens to the crankshaft on a long engine like the straight six:
- It goes wet noodle when under load.-

These animations are the best I could find to explain this visually.
Each firing event bends the crank slightly.
Then due to the firing order and location on the crank, harmonic vibrations are developed.

Starting at 0:45, it very simply shows the force direction on the rod bearings when in operation.

While this animation is not of a straight 6, it does show very well the forces that a firing event induces on the crankshaft.
Also the corresponding wave through the crank causing bending at either the crank pulley or flywheel.

Here is a whitepaper on the subject if anyone would like some light reading in their free time :D
another

Long story short, don't run without a dampener.
Its a problem waiting to happen.
 

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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, instea my ip birthday wishes tneb d 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!
When will the new software stop these obvious bots?
 
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