I think its the opposite...if its underdriven the pulley would be a larger diameter.

 

Gruppe-S's pulley is not underdriven..i didnt notice anything besides performance wise that changed.

 

If it's on a device being driven. i.e. alternator, AC, PS, then larger pulleys are underdrive.

If it's on the crankshaft providing the power, then smaller is underdrive.


I have also heard of the lightwieght pulleys allowing harmonic frequencies to effect the crankshaft. At high RPMs, this can be bad. I've never heard of a crank exploding though, so maybe it's just someone talking out their *** on the internet. That happens once in while

 

Why don't you put in the i-Club Reviews section so all can see and post their experiences too? There is a place to upload upto 3-images with the description. And after a place for the reviews...just a thought.

https://www.i-club.com/reviews/showcat.php?cat=114

 

Is this lightened pulley rotationally balanced?
I don't believe anyone has done a multi-axis rotationally balanced lightened pulley yet.

 

yes the vishnu is lightened and underdriven, though only slightly. Sorry ^^; i'm not sure if the engineering concerns are more from diameter or from weight (sorry, my asian science specialty is biology and more recently logic, not any of the maths ^^;;; )

Forgot to mention, the biggest decrease felt by the UD pulley i had was in the A/C... the decrease here was noticeable.... it's not WARM or anything, but you definitely notice it not being as cold as before. Still colder than fan though. I never use the A/C unless driving my parents somewhere (and that's probably the only thing keeping me from having it removed, spec-c style) so it's not an issue for me... but worth noting.

Didn't know about the reviews ^^;; thought I'd put information where it was being discussed... I'll move/repost there when dsl is live in a few ^^

 

So I got a great idea then. They have these awesome CF driveshafts for VR4's that weight like a third as much (15 vs. 47 lbs or something)

So if a crank pulley that takes off 3 lbs of rotating mass gives 5 hp, a CF driveshaft saving 30lbs...

See something sounds wrong with that. I'm not saying crank pulleys don't work because I have one and I think it definately feels faster, just saying that most people (including me) misunderstand/do not fully understand exactly what is making the performance gain.

 

performance gain because its taking Mass off the crank meaning the crank doesnt have to use that much energy to rotate the crank pulley.

 

That's obvious. What's not obvious is the quantifiable correlation between rotating mass and increases in the ability to accelerate, whether that relationship between rotating mass and whatever performance metric you choose to use is linear or not.