Quote:
Originally Posted by SS_Firehawk
Don't put words in my mouth. Aftermarket pulley's have not shown to be a catalyst of engine failure for our specific engine.
|
Of course not. This isn't a 'grenade the engine in 15K miles' sort of issue. It will be extremely subtle and dependent on driving style. The resonance range is probably <500rpms.
Quote:
|
The stock pulley is not a harmonic dampener to remove potential damaging frequencies.
|
source?
There's no question that the stock pulley gives the complete system a lower Q factor than any of the aftermarket pulleys available. Cast iron and rubber are unquestionably more efficient at translating vibration to thermal energy. Hysteresis loss is far higher in an iron/rubber assembly, vs an aluminum one.
Quote:
Torsional effects are mitigated by balancing the entire rotating assembly and adding counterweights to the crank. No external balancing was necessary.
|
The internal balance you describe is insufficient to completely mitigate the need for the damping we are discussion.
I'd love to see a source for the bolded part.
Quote:
|
Engineers that work on designing and manufacturing factory engines have advanced engineering to the point where in most cases, external balancing and/or harmonic dampeners aren't necessary.
|
external balancing is not the same thing, and it is more or less impossible to completely eliminate the need for an external damper while still achieving the reliability levels expected from modern cars.
Quote:
Originally Posted by SS_Firehawk
Just to clarify for what that rubber ring is for, it's to balance the pulley it's self. I wouldn't doubt it's to assist N/V/H as well, but we all know our engine is not the silkiest around.
|
you keep saying this as a fact...I'd imagine it would be hard to determine this just by looking at it...
Quote:
Kyle @ Stillen asked Nissan engineers about it on an old thread
"This is a harmonic dampener of sorts, on that point you're exactly right. But it's not to balance the engine, it's to balance the pulley ITSELF."
|
link? preferably with something other than a vendor backing the claim.
I'd be confused as to why a pulley needed a "harmonic dampener of sorts"
Quote:
Originally Posted by SS_Firehawk
You haven't seen the size of it to fully understand. It will rot out well before the engine breaks. Is the motor going to explode when that happens? I'm pretty sure it won't. I'll be surprised if it lasts 15k miles before it rots.
|
The rubber looks to be intact on all the high-mileage Z's I've seen. There's actually a lot of effort put into finding good materials to use in these applications.
Quote:
Originally Posted by SS_Firehawk
Maybe you should have read the original thread, and if we have a harmonic balancer, damper, dampened pulley, whatever name you want to give it, wouldn't you see one on the car? Look at the crank pulley, remove the damn thing and look at it, there is nothing about it that dampens harmonics. It keeps the motor from dropping revs too fast, just like the stock flywheel in an attempt to keep drivability in tact.
|
Serious question--do you have any background that makes you qualified to discuss resonance? I'm curious what you are basing the bolded portion on. It would be quite impressive to be able to look at that component and visually determine that it did not serve any purpose in damping vibration.
Quote:
|
Data is in the numbers. Name or show one, just a single VQ37VHR motor that had catastrophic failure that was absolutely, without a fraction of a doubt caused by an aftermarket crank pulley that was installed correctly. Do you really think I would come into a debate and not do my homework on why you argue against light weight pulleys? Only a fool debates without research. Show me concrete evidence. BTW, I've read both links before you posted them a while ago. There is no talk of an undampened crank pulley with the exception of low RPM V8's.
|
The lack of directly linked catastrophic failures really doesn't show much. Most folks don't drive their Z's much, and the effects of mild, occasional impacts will manifest themselves slowly.
I absolutely agree with the first statement here. Data is in the numbers. Would be fantastic if a pulley vendor gave us a graph of the frequency response of the crankshaft with each pulley installed. THAT would tell you something.
Quote:
|
I reckon your the one that needs to do some more reading before you blast my posts. This isn't the 90's anymore, engine's evolve.
|
Engines have evolved, but the physics behind resonance haven't.
Quote:
Originally Posted by Trilitheum
Just to add some more data into the debate, here is the US patent for a plastic hub torsional harmonic damper which has some good graphs that illustrate the effect on crankshaft twist in degrees vs engine RPM for various damper configurations including no damper.
Even if the engine is perfectly balanced there will always be torsional pulses which can and do form harmonic modes as a result of the discrete, not continuous combustion pulses (each cylinder firing in turn). Balancing the entire rotating assembly will not stop rotational twist of the shaft from the power pulse as each cylinder fires. It will stop out of axis oscillation.
The pulley being made out of cast iron is also on purpose, cast iron has one of the highest dampening capacities (google cast iron damping) of any metal.
If you don't want to read the whole document look at Figure 2 to see the effect on torrosional vibration via a typical damper (construction shown in Figure 1)
|
Cool link. Pretty crazy to look at old patents and realize how much of the work was done through trial and error.