In our experience we have seen many highly modified EVO's and Subarus using aftermarket pulleys that have had them on for years and many miles without engine failure. We've also seen many highly modified EVO's and Subaru's with the factory pulleys with spun or severely worn bearings.

In my opinion it is simply tuning issues that is causing these failures. While a lighter crank pulley and flywheel MAY magnify poor tuning, the root cause of failure is still poor tuning. I have yet to see conclusive proof that harmonics from the lack of a dampened crank pulley is the root cause of failure on on these engines (Edit I'm talking bearing failures not cracked pistons or throwing a rod through the block ). I run lightened crank pulleys on both my EVO and WRX. My WRX probably with 40,000 miles on this pulley, GT30R turbo, with a Link ECU (no knock correction on). No problems so far - and it just revs so much faster


Cheers,

Gary
Gruppe-S

 

I am gathering up proof that the factory harmonic balancer is indeed tuned to counter-act vibrations found in the stock configured block. It is a mathemical model, and have drawn upon a few sources which have done lab tests on actual crank shafts. These resonant frequency vibrations do INDEED exist, and they DO cause damage to the crankshaft, there is no denying that. Anyone not using a harmonic balancer/damper is definitely playing with fire. Whether or not the stock balancer is any better than an aftermarket fluid damper is still unclear.

 

I fail to see how modifying a pulley's weight has anything to do with a harmonic balancer.

I sincerely doubt a pulley with 4 bolts attached are going to stop vibrations that get through the dampener.

 

I wonder if the harmonic frequencies are caused by severe detonation rather than the standard combustion process?

Cheers,

Gary
Gruppe-S

 

All forced oscillating systems (like a crankshaft rotating in a cylinder block connected to rods + pistons, flywheel + clutch) have their associated resonant frequencies (i.e. 200 hz, 5.5 mhz, 2000 RPMs, 7400 RPMs, etc) and where their harmonics appear at depend on the rotating/oscillating object's "natural frequency". Every oscillating object has a "natural frequency" and it entirely depends on the shape/material and how the mass of the material is distributed across the object (more dense at one end than the other). Have any of you seen the video of the Tacoma Narrows Bridge in Washington State? The entire bridge (made out concrete/steel) was jumping up and down with huge waves rippling across its entire length. This is the most famous example of resonant frequency. The entire bridge (composed of many interconnected parts and materials) had a low natural frequency that matched that of the current of the passing water underneath it. Consequently, the entire bridge started to vibrate at this frequency until the amplitude was so great everyone could observe it. To learn more about this topic please visit:

http://science.howstuffworks.com/question603.htm

http://www.glenbrook.k12.il.us/GBSSC...nd/u11l4a.html

The problem is, when energy is imparted onto an oscillating object at it's natural frequency, the vibrations at this frequency are amplified greatly, often causing damage to the oscillating object (opera singer shattering glass, bridge jumping up and down, spun bearings in an engine block). If you still think that putting on a un-dampened pulley is a good idea, please do some more research. I cannot say for sure whether or not the factory harmonic balancer is any better or worse than afterkmarket fluid dampeners, but I am still investigating. Hope this helps.

 

^ this is a good developement of topic. to elaborate i'll say this.

an engine is a driven oscillator. this is obvious. oscillators driven at resonant frequencies will experience high amplitude oscillation.

picture this. ever seen an unballanced wheel on another car on the freeway. it's hopping up and down. why?

because the wheel is driven by the road (yes by the car on the road but let's look from the car's perspective) as the road drives the wheel the weight from the unbalanced wheel gets flung up on the up cycle and flung down on the down cycle becuase it wants to rotate at it's center of mass but is HELD at it's geometric center.

now think of a crank shaft looking down the shaft. each time the piston fires it deforms the crank shaft lever arm a little (there's two arms per piston). now this might be ok when there's no resonance... but when resonance happen what does the situation become???

when there's no resonance the piston "twangs" the crank arm much like if you held a ruler at the end of a table and twanged it. you see the oscillations get smaller and just stop eventually... a non resonance situation is when you twang it once and when it comes to a stop you twang it again. let's say you're dealing with a really LONG metal ruler so the oscillation is nice and slow... you can twang it and when it's on the upswing you can twang it again. that's also not resonant.

resonance is when you take this long metal ruler, you twang it, then when it's on the down swing you twang it again so the distance traveled gets bigger then after one upswing on the down swing you twang it again... you keep hitting it on the downswing the distance traveled will eventually get so big that the ruler will just bend.

now picture that VERY FAST like in your engine... on a crankshaft. where's the pressure exerted? well you can imagine in the case of the ruler your hand is holding everything down and when the ruler bent it woulda been near your hand. what about on the crank? it's on where the crank is HELD right? bearings....... or you just snap the shaft right near the bearings.

 

When I disassemble my engine within the next few thousand miles, I will have compiled some 35,000 miles of use with an aftermarket pulley, with three different turbos. This is the first time I have eliminated the dampener on any engine, and I've been through quite a few. I will perform a thorough inspection and let that influence me one way or another.

 

wow i can't believe some of the comments i just read. first of all why try & save weight on a crank damper !!??? it's to risky. save weight somewhere else, like the flywheel.

if your engine has stock internals, your stock damper is fine until 90~100k or so, when the rubber starts to go.

from fluidamprs website:

"Each time the air/fuel mixture inside a cylinder is ignited, the combustion that occurs creates a torque spike that is applied to the crankshaft through the piston and rod. This torque spike is so severe that it not only turns the crankshaft, it actually twists the crankshaft ahead of its normal rotation and then the crankshaft rebounds. This twisting action is known as torsional vibration. When these torque spikes and forces get into phase with the natural frequency, critical torsional harmonic vibrations occur and can be seriously destructive to the bearings and the crankshaft. Dampers are designed to control those destructive vibrations.

Critical harmonic vibrations occur numerous times in a engine’s operating range. Stock rubber and elastomer-type dampers are frequency sensitive “tuned absorbers”, and work at only one critical frequency. In the case of a stock rubber damper, it is tuned for a factory engine’s critical harmonic vibrations. If you change the mass of pistons, rods, or the crankshaft, you change the natural frequency of the crankshaft assembly; therefore, the stock damper is no longer tuned to the new frequency of vibration, and you may be headed for early failure of expensive engine components. Dampers also create heat while they work, and rubber is a poor dissipator of heat. This heat and the exposure to the elements deteriorates rubber, causing it to crack and change durometer, which then leads to inertia ring slippage, damper failure, uncontrolled torsional vibration, and costly engine parts breakage."

 

G-unit - thanks for posting that. As discussed, going with lighter internals and flywheel changes the resonant frequency of the entire rotating assembly. Since the damper is "tuned" to this frequency and the frequency changes based on the composition of internals doesn't this invalidate the effectiveness of the stock pulley anyways?

I'm just pointing this out, because with a good balance, tight tolerances, good bearings, and a good tune we aren't seeing any failure problems with the 4G63 or the EJ2X series engines regardless of pulley employed.

As for the Tacoma narrows bridge (I have taken a few structural / civil engineering classes) I'm not entirely certain how this applies to the crankshaft / rotating assembly.

Cheers,

Gary
Gruppe-S

 

Balancing the rotating assembly has nothing to do with harmonic vibrations. These vibrations happen on ANYTHING that moves in cylcles (i.e. pendulum, engine, rotary, sound waves, light waves, magnetic/electric signals, wind, water, etc.). If you have a very unbalanced rotating assembly, YES you will feel vibrations, but they are not harmonic vibrations. Say for instance you remove your balance shafts and install prothane motor mounts. You are definitely going to feel certain "vibrations", especially at idle. However these vibrations are felt because a certain component or area of the rotating assembly is heavier than other parts (like when you have a tire/wheel that is out of balance) and is a totally different issue.

 

Absolutely agreed.... I have been an early user of underdrive pulleys for many years now but only learnt about the detrimental effects of harmonics in the 4G63 engine not too long ago.

Try replacing bearings every single race like I do and you will know that the problem lies more than just tolerances and balancing. Have been building 2.0 on the DSM's for years now and the inherent bearing problems but thank god I nitrided my cranks ( thus am able to save cranks even with worn out mains) and 2.3 strokers in my Evo 6 which kills absolutely every single mains running only 6 to 7 passes on a single event. And both makes over 700WHP. Both have not run harmonic balancers and without balance shafts. And yes, the engine DOES make a little more vibration without the balance shafts. Funny thing is that while the main bearings are worn out badly, the conrod bearings remain perfect, almost untouched....

Have recently completed a race on the stroker and will remove the main bearings shortly to compare previously on which I have ran no dampener and this time with the dampener. This will at least confirm some how on the effects of the dampener.

Am only relating my experiences with the harmonics that are killing the engine and I don't think Mitsubishi would be putting one on if it didn't need one...

If I recall in one of many early forums some long time ago, even Bushur runs the stock dampener and doesn't use pulleys....

 

yes your stock damper is tuned for your stock internals. so if you change something, then a aftermarket damper ( not lightweight pulley) will work at any frequency, controlling destructive torsional harmonic vibrations.

i know i would not buy a used evo with a lightweight under drive pos pulley installed on it.

 

The cranks of V6, V8, and I6 engines are more susceptible to harmonics than an I4. This being the case, where are all those hopped up Chevy, Ford, and Mopar V8s with broken cranks and poor wear patterns that we never saw, despite the 'fact' that reusing the stock dampener was worthless because it was suddenly 'invalidated'?

This was never a problem because it didn't happen.



Please post the results. If you know what to expect, it will be interesting to denote any obvious deviation.

 

We shall eagerly await your findings. Thanks for posting!

 

This might be a dumb question, but why is the I-4 less susceptible to harmonics?