Quote:
Originally Posted by Red__Zed
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.
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.
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.
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.
you keep saying this as a fact...I'd imagine it would be hard to determine this just by looking at it... 
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"
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.
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.
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.
Engines have evolved, but the physics behind resonance haven't.
Cool link. Pretty crazy to look at old patents and realize how much of the work was done through trial and error. |
Here is the issue regarding arguing my points. There isn't an aftermarket company on the planet that has the R&D of a car manufacturer. Due to the nature of the industry, Most Engineers that design cars are not going to expound in much detail, if at all on why they may have done things a certain way. There is plenty of research on resonance, torsion, N/V/H, and negative harmonics because it's already a known. Most of my findings are from manufacturers, but also reading about the issue at hand. I haven't read a single cited source that has said specifically, the way our pulley was designed, that it is a dampener of potentially destructive harmonics. Every description and engineering paper I read shows a rubber dampener that is encased with the rubber set vertical, or viscous. Ours is horizontal to the motor and only about 5mm thick. It looks like it's preventing all the accessories from vibrating or introducing more N/V/H to the crank as opposed to removing bad harmonics from the engine itself.
Every car company is going to say, leave your engine alone and it will be fine. Every aftermarket company that makes parts for said manufacturer is going to say, "Buy this and it will be even better" Who do you believe? Forums like this is feedback from everyone. I said it before, take everything you read in here with a grain of salt. Yes, even everything I say and argue about, which I admittedly do a lot sometimes. I'm not out to convince the World, but there are always two sides to the story. Obviously, it's difficult to go wrong with a stock crank pulley. I 100% agree. I also believe a well engineered aftermarket crank pulley can be safe to use. Some do not. People ask why, we say what we think, preferably have relevant source material to back our findings. Could I be wrong? Absolutely. Is the Bible indisputable fact? Do you believe every animal floated around Noah's ARK for months and the entire Earth flooded?
I used the word mitigate because regardless of internal or external balancing, spin a motor fast enough and even the best motors can grenade to harmonics. If Nissan plans on spinning the VQ to 9-10,000 rpm or higher, I'm pretty sure we would see a different crank pulley, maybe to a true dampener.
FYI, I never stated my finding's as absolute facts. I listed my arguments to the topic.
Regarding my statement about external balancing not being necessary, it is absolutely true for some smaller displacement motors. I think the VQ fits in this category, but there is room for argument there.
Lastly, and I'm repeating myself, DO YOUR OWN HOMEWORK AND COME UP WITH YOUR OWN CONCLUSION!!! I'm tired of people giving recommendations like it's fact and not letting them decide for themselves by only giving them one side of the argument.