Destroying the dogma: lightweight crankpulleys

[Trab]

Maxclass, i think that you should sell me your stocker. lol Nah if i was you i would reuse my stock one.

[green-lantern]

Just so you know what your bidding on.............

yeah that's it.

[Tackhammer]

That one is/was made by Fischer
I was a dealer back in the day and tried to do a group buy @ $350 and was quickly laughed out of my own thread
I said screw it, got one for myself, and never mentioned it again

[i3igpete]

Again, this kind of buildup occurs mostly at constant engine speeds (cruising, etc), but still happens to an extent under all conditions.

This picture here is a bit misleading. the vibration shown here is a bending mode, which is usually the 3rd or 4th natural frequency (very high Hz), and is basically impossible to tune out. This is fine since each vibration mode has progressively less excitation.

One thing to note that these papers don't mention is that resonance builds up quickly. From steady state unloaded crank it only takes 5-6 engine cycles for the crank to reach vibrational convergence. at 6000 RPM that works out to be just 0.05-0.06 seconds. The problem is that in reality, the crank is already vibrating quite a bit at 5800 and 5900 rpm.

The string analogy is good, but a better analogy for those with a musical background is a brass instrument. the vibration gradually gets drops off at slightly higher or lower RPMs - it's not an on/off switch. for a given overtone, although you may be playing the right fingering on the trumpet, you may be flat or sharp due to your lip buzz frequency.

[TonyM]

How about seeing what fluidampr would charge for a group buy????? I wish there were ones better than stock. Though I just bought a new OEM one.

I had contacted ATI about making one but another member at 3Si had already been doing the same for some time prior. I let it go at that point and he hasn't posted any updates since. It really shouldn't be too difficult for ATI to reproduce a streetable damper for the 6G7X as they've done speciality one-offs for drag cars in the past.

Expect pricing for something like this to be at least $750 plus the machine work to have the hub pressed on to you crankshaft. It's not a cheap mod but would be beneficial for the big dollar builds where you have thousands wrapped up in the bottom end.

[bluemax_1]

Well, if the article is correct that viscous type dampers are better than the elastomeric dampers (and elastomeric dampers optimally need tuning with the elastomer durometer etc.) who's going to approach Fluidampr about making a pulley for us? Especially since it appears the ATI thing stalled out and is dead in the water.


Max

[EvanH]

One of the big guys. Sponsors?

[RL7]

The belts are rubber. Don't they have some dampening ability? The rubber strip in the oem pulley isn't much larger. I'm currently using a lightweight pulley, but that's only because my oem ones were chipped. I also saw pics of oem pulleys that came apart at the rubber and it didn't look like a fun thing to have happen. Those failed oem pulles were undoubtedly very old though.

[DanF]

Nelson had ATI make some Super Dampers for his engines. Of course that's hardly an affordable solution.

[i3igpete]

in a word, no. consider the thickness of the rubber ring and the shear surface area - overall, it is very stiff because it's tuned to match a vibrating piece of steel. then consider a length of timing belt or accessory belt - a very long piece of rubber with very small cross sectional area. it is so soft that it is basically ignored by the vibrational torques in the crank - typically 4-6 times that of the output torque (thats 1200-2000+ ft-lbs of twist that the journals see)