Lightweight crank pulleys?
 

I've been doing a bit of reading on lightweight crank pulleys lately and am finding conflicting information. Some of which says they're a very bad idea since they can't absorb any of the noise/vibrations but other info stating the stock pulley with rubber ring does nothing more than try and quiet down engine noise (it is called a harmonic damper after all). I know underdrive pulleys are available too but I'm not really concerned with them, mainly just looking for info on solid aluminum vs. dampened (stock or Fluidampr for example).

Re: Lightweight crank pulleys?
 

Some people say the undampend ones can ruin your oil pump with vibration, others have ran them for 100s of thousands of miles with no trouble, it is hard to find a solid answer though im sure you have found that out through your research.

Re: Lightweight crank pulleys?
 

If we are to trust that Fluidampr and ATI know what they're doing (and I do) then there would definitely be some adverse affects when using a crankshaft pulley. A lighter weight pulley will free up some horsepower, but it will adversely affect the longevity of your engine bearings. When, if ever, will a failure occur from this is the question, but is it really worth the risk?

From Fluidampr:

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.

Re: Lightweight crank pulleys?
 

My other thought is, can the little stock pulley with a rubber ring really do much good at absorbing vibrations when there is the much larger and solid flywheel at the other end of the crank?

I've also read about the vibrations potentially damaging the oil pump, but, does the stock damper even affect the oil pump since that's driven off the timing belt and not accessory belt?

Maybe I'm just confused as to what vibrations the dampened pulley is actually absorbing that couldn't otherwise be absorbed by the rubber belt and tensioner. How exactly is it able to protect the engine bearings from vibrations?

Re: Lightweight crank pulleys?
 

Interesting article from Steve Dinan:
http://www.atiracing.com/products/da...mper_dinan.htm
But then I did a bit more looking and Dinan sells the under-drive pulleys for BMW's and makes no mention of them being dampened...

Re: Lightweight crank pulleys?
 

Vibes are a COMPLEX subject. Suffice it to say, yes the rubber coupler on a stock crank pulley is designed to absorb certain destructive frequencies. Factories are out to save money, they wouldnt put it on the car if it wasnt worth the effort vs using a solid cast piece.

That said, i've been running a fluidampyr for going on 4 years now.

Re: Lightweight crank pulleys?
 

I'd have to be hard pressed to use a non-dampened pulley on my car. The pros outweigh the cons, I don't see a logical reason to convince yourself or anyone else to use a non-dampened pulley.

Re: Lightweight crank pulleys?
 

How I understand it is this. Sound can shatter glass at the right frequency and db level. Each time the piston is on its power stroke it flexes the crankshaft and then the crankshaft reverts back to its original state. At 6000 rpm, that would be 100 hertz, or 100 times a second. Its a low frequency but the load is pretty high. The crankshaft will shatter or split/crack at its tuned frequency, just like a glass. Now fill the glass with rubber, it will no longer shatter at its tuned frequency. The damper takes those vibrations and eliminates it as heat.

Me, I bought a fluidamper for my 2.4 because I got sick of the stock damper cracking and slipping on my 1g. Id never run an undampend crank.

Re: Lightweight crank pulleys?
 

Soo, jist of the story: run a ATI/fluidampr, and get rid of stock.

Re: Lightweight crank pulleys?
 

Can you prove any of that? You tube video of a crankshaft shattering at some frequency produced mechanically or via air?

The quest pulley is a solid piece, and while I haven't cut one in half to really verify, it's obvious it's a fully machined unit and not assembled or built around rubber rings or fluid. I personally wouldn't worry about a solid pulley, and if you ever did reach the resonant frequency of the crankshaft just by running it (which you probably won't) you'd only be there for a split second, then the RPM's change.

In my completely uneducated guess, I bet it helps with load changes from alternators, PS pumps and A/C compressors more than anything else. If your crank is vibrating, a damper outside the engine where the bearings aren't will do what, exactly?

Re: Lightweight crank pulleys?
 

I came across an interesting post by ACTman on EvoM (he works for ACT) stating that Brent Rau was having issues with his flywheel bolts coming loose until he switched back to an OEM crank pulley. Also found some info basically stating that although a solid pulley won't break your engine, it will wear the bearings faster. The more power the engine makes the more issues that arise it seems.

Re: Lightweight crank pulleys?
 

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

Reading matierial

Re: Lightweight crank pulleys?
 

good link :)

Re: Lightweight crank pulleys?
 

Note, harmonic dampers do much the same thing as balance shafts, and we all get rid of those, don't we?

Re: Lightweight crank pulleys?
 

Balance shafts reduce overall engine vibrations, where as a crank damper reduces vibrations more specific to the crankshaft.

Re: Lightweight crank pulleys?
 

Exactly. The balance shaft is there to not transmit vibrations to your ass when you are sitting in the car. The harmonic balancer is there to cancel out crankshaft vibrations.

Re: Lightweight crank pulleys?
 

I think the reason is when the crank is twisting slightly from the torque output of the rods, that resonance that can occur is the crank basically jerking foreword and then back, kinda like a rubber binder, at a certain frequency that vibration will be very dramatic compared to normal (its resonating frequency). The crank pulley being attached to the water pump and alternator has rotating energy, and like Blackrosenova said, the rubber absorbs those vibrations... I cut metal for a living, you realize how harmonics can affect metals, and what slight changes it takes to fix them...

On a side note, not all engines need dampening, just certain cranks will resonate at a frequency that could be made under use.

Re: Lightweight crank pulleys?
 

Thanks for all the thoughts, opinions, and facts guys. I'm glad I started this thread as its pretty much reaffirmed what I initially thought. A local guy down here just installed the Perrin pulley and it got me to thinking what exact purpose the stock pulley serves.

Re: Lightweight crank pulleys?
 

<- beefcake crank that doesn't rev. I don't need no stinking damping! ;)