I think a few of us are missing DaveB's points here.

-The UDP may be ten times more perfect in circular dimension but this doesn't dampen the crank.

-The stock pulley will do a better job of dampening the crank period.

-The UDP will cause wear on the egine components more than a stock pulley. Albeit very little wear.

While the following is understood by everyone.

-The UDP does allow the engine to rev faster, sacrificing less power to rotational mass then the stock pulley, thus transmitting more power from the engine to the wheels. Physics.

Like any aftermarket performance mod you are going to be trading one thing for another, most often reliability/longevity for performance.

In this case it seems that the reliability/longevity is lowered minimaly, while on the other end performance (getting from point a to b) is increased minimaly as well. Now we can argue the amount of change on the latter side of the spectrum all we want but it seems that DaveB's points are correct. His opinion on whether its a worthwhile mod is debatable.

If I may be so bold as to offer the Final Word:

-The UDP will cause more vibration from the crank to transmit through.

-The UDP will cause more wear on the engine components.

-This increased stress is very minimal and no record of failure due a UDP has been recorded.

-The UDP will allow the engine to rev faster and lose less power to rotational mass in the power transfer from engine to wheels.

-The hp increase to the wheels, mind you we are freeing up power not making more, is minimal like nearly all NA aftermarket mods for our particular cars.

Its your money spend it on what you determine to be worthwhile.

 

Glue a rubber band on the UR pulley and call it good.

My lead average is 2 ppm while the universal average is 6 ppm. My bearings are doing 3 times better than the average.

Again, mine and the other blackstone reports seem to indicate otherwise.

 

I don't think you understand how serious a racer I am and how consistent my car is. You can mess up ET by simply spinning the tires too much on launch, but your trap speed is dictated by available HP. You can't F that up unless you have a super terrible 60 like a 2.5+. I've run 14.3@99mph with high 2.1 60 foots and 14.6@99mph with high 2.3 60 foots. I am well aware of conditions too. Everytime I run at the track it's with 95 octane which is a mixture of Amoco 92 and a little 100 race gas and the same setup. And no, when I go to the track, I'm terribly consistent. We're talking within less than a .1 and .5mph between runs with the similiar 60 foots and 30 minute cool downs. Once in a blue moon I'll blow the tires off on a launch and get a higher 2.2 or 2.3X 60', but it's rare. Very rare. 95% of my racing has been at the same track and I've got about 170 timeslips for that track. I write down baro pressure, temp, and humidity on the day I was there so that I can correct the slips to density altitude in an effort to make the best comparisons in performance. Every real drag racer does this so that they can gauge if a mod or setup works or doesn't work. You'll hear drag racers say things like "the DA was horrible today" or "conditions are great because the DA is well below sea level".

I'm not some ignorant racer that puts an UDP on his car and goes from 14.6@95mph with a 2.25 60' in 90 degree weather to 14.3@98mph with 2.10 60' in 55 degree weather and claims the UDP improved the performance when in reality it was the better 60' and better DA that improved the performance. I don't know how many times I've read posts in this forum and Maxima.org and elsewhere where guys claim such BS.

I don't dispute the laws of physics concerning the UDP, but you're not taking into account the other things that occur when running an UDP on a VQ. I mean seriously, how much HP do you think that 2lb lighter pulley is really going to make? The guys at Unorthodox are idiots as far as I'm concerned when it comes to the VQ. Thier power claims are also rediculous.

 

If you're name was kenny brown or they called you 'big daddy' on the track, I'd still go with the laws of physics. If you're variance is actually .5 mph and a tenth, didn't it get somewhat monotonous and boring after, say, the 150th run?

Unless you intentionally meant to mis-inform or exaggerate, your self-proclaimed status as an expert here seems to be suspect. Actually, it's closer to ~7 lbs IIRC.

 

Al503 I know you're gonna get pissed but...

Although getting an analysis on the oil can tell you about metal content and bearing wear rates, it wont tell you anything about creeping metal fatigue.

With "x" number of degrees of tortional twising on a crank shaft at a given resonant frequency the number of un-damped tortional load cycles will add up very rapidly. Each cycle will stress the metal to some degree and with a resonant frequency that could be anywhere between tens to thousands of hertz it could add up to metal fatigue. Metal fatigue is a process that can eventually lead fissures within the micro structure of the crank shaft metal.

IMHO I am sure the Nissan engineers considered this. Otherwise why would they choose to sacrifice performance on a heavier, costlier damped pully? What a waste.

It would make absolutly no sense unless there was a projected need for it.

I sure don't want my crank shaft singing like a tuning fork. It would light up nearly every moving part in the engine. Mabey it's well within the limits of the engine but I won't advocate it.

And no, I am not an expert on reciprocating engines. I'm just extrapolating from what I know as a aerospace engineer & rocket scientist.

 

No reason that I can think of to get pissed off.

Being an aerospace engineer and rocket scientist (don't know if this was said with tongue in cheek or not. A rocket scientist alludes to someone very intelligent in my mind who should be able to spell an engineering term such as torsional correctly), you should probably understand that the weight of a particular component is based on more than just one factor. Not being an engineer or a rocket scientist myself, perhaps the engineers wanted the owner to be able to launch the car in first without killing/stalling the engine (driveability). A heavier pulley would help in this regard. The G isn't a dedicated race car. By definition, compromises between civility, driveability, and performance have to be struck.

In addition, I would argue that the stock pulley is not more expensive in 2 regards:
1. Raw material: aluminum is more expensive than iron/steel.
2. Manufacturing: casting v. milling: the former is much cheaper than the latter.

As mentioned above, if the pulley was indeed as important as you mentioned, it would be milled from a homogeneous block of metal instead of being cast from who knows what, which would introduce the possiblity of manufacturing variances.

 

Al, actually it's the rubber that's the most important part since it is the dampener in the assembly. The quality of the metal in either case is probably not a real issue in this case. In everyday use this is all most likely moot. However if somehow you spent a lot of time in the resonant range, life might get interesting for your bearings and some other parts. It's all personal choice but there are some real drawbacks to street driven UDP. And just to be a butt, I am, among other attributes, a physicist. But not a rocket scientist......

Merry Xmas and Happy Holidays in an inertial sense

FYI, some more good references to help you make up your own mind:

http://www.team3s.com/FAQudp.htm

http://www.cprparts.com/products/dampers/romac.html

http://www.hotrodders.com/t24413.html

http://www.cartunerz.com/aem/aempulley.html

http://www.3000gtvr4.com/pages/underdrivepully.html

 

JCV, first of all, good to see you being more active on the boards again.

I am informed and from what I can tell from a visual examination of the stock pulley, the rubber does not go through the pulley itself. It is in a little slot on the surface of it. Dinan wrote a piece on lighter aftermarket pulleys and he concluded that if the aftermarket pulley doesn't have a piece of rubber that goes all the way through it, (like the oem stock bmw pulley), there would be a risk of premature bearing wear.

If our oem stock pulley had a piece of rubber that went all the way through it, I would have never gotten the pulley. I know a little bit (not an expert) about harmonics as the company I work for provides steel for seismic retrofits on bridges across the US, among other things.

A little strip of rubber is not going to do much to tame this torsional vibration. I've read that it's purpose is to quiet the belt noise.

In terms of my bearing wear (which is ostensibly what one should be worried about), mine is almost non-existent and much better than the universal averages. That was with a full track day on it also.

I think the VQ is a very robust engine. There have been no reports of detrimental effects on any forum. This includes maxima.org whose owners have had UR pulleys on their cars before the g and z existed. People running them who have tested their oil have come up with good results. All the concrete evidence is positive.

 

The resonant frequency of any fan belt will be far too low for the pully damper to do attenuate it, but that little strip of rubber will become a very powerful damper (absorbent) at high frequencies (>~1000 Hz) and the resonant frequency of the crank will probably be much higher than that and well within the range of the pully damper.

It's really very simple. Imagine the effect of placing a pice of gum on one, or both, ends of a tuning fork. Despite the relatively low mass of a piece of gum, the resonant frequency may not change much but the tuning forks ability to resonate will be highly damped.

The gum on the end of a tuning fork, and the rubber on the end of a crank shaft pully are functionally the same. Vibrational energy can be transmitted into the plastic but it cannot be reflected back to any substantial degree. The high frequency vibrations are converted to heat.

I have designed and qualified rocket engines for use on JPL's Europa Orbiter and many other sattelites. Even with my occasional misspellings I won "Best Propulsion Paper" at A.I.A.A.'s Joint Propulsion Conference in 2000. And won NASA's exceptional achievement award for the TDRS-I recovery mission in 2003. Hold a couple patents and even design ramjet engines.
But no, I never won a spelling bee. (sp?)

 

Hmmm. I don't think you have any way of backing up your opinion on what frequencies the rubber would or would not dampen. The composition and physical make-up of the rubber will determine which frequencies it actually dampens. Some rubber compounds dampen very low frequencies such as those produced by subwoofers which are around 200hz and less while others are better at higher frequencies. Unless you've taken the pulley out and measured it with and without the rubber strip, you have no basis to make your claims.

I actually took a look at my stock pulley this evening. I had it in for no more than 3k miles in about 2 months before switching it to the UR pulley. The rubber already has cracks in it. I wonder what happens after longer exposures to the heat, cold, dirt, ozone, etc?

Would rubber with cracks from dry-rot that gets progressively harder from thermal cycles continue to dampen the 'critical' frequencies, whatever they may be after a year, 3 years, or even 5 years?

 

Rubber compound has some influence, but the cracks don't make a hill of beans since the part is in compression/torsion. Design including rubber thickness and loaded area do. It's something called "shape factor". By the way Al, almost all highway bridges and many building in earthquake areas are on rubber sandwich dampeners, that gives some idea of the energy absorption the devides are capable of. Sure don't want to change those to UR components. Also, ask the audio or aerospace engineers about constrained layer dampening for energy absorption.

What everyone here is making noise about is inertia, not horsepower . The pulley doesn't add any horsepower (even UR admits this) but it responds to acceleration changes more rapidily. Great for road racing and engines that are rebuilt routinely.

Merry Xmas and Happy Holidays

 

It's called "engineering judgment" we are often forced into these types of calls at my work when a real analysis is not possible. The judgment is based on prior experience, feel or intuition. More often than not it works well.

Yes and no...

Yes,
The material composition can make all the difference. If it was a very hard plastic the damping frequency would be raised considerably but it would damp only very high frequencies. If it was a very soft jel the damping frequency would bel lowered considerably, but unless it was completly encapsulated it probably wouldn't be tough enough to handle the job.

and No,
Being a rubber, which typically implies a general material property, it would work as a good damping material for resonating metal parts. And being described a strip of rubber on a pully, it is reasonable to assume the thickness of the rubber is anywhere between 1/16" to 3/8" thick.

It would not be reasonable to assume a 6" thick block of rubber was glued to the pully. It would have good low frequency damping abilities but would be impractical.

It would not be reasonable to assume a 0.006" thick membrane of rubber was glued to the pully. It wouldn't damp vibrations of any kind and wouldn't be worth the effort or cost of putting it on the pully.

And, it wouldn not be reasonable to assume the intelligent, maticulous engineers of Nissan would arbitrarily put a damper pully on a crankshaft for no reason at all.

-------

Merry Christmas everyone!

 

This thread is starting to look like something from the American Physical Society or SAE. We are going to give tests when all is said and done. Now all we need is someone from UR to jump in for a skewering.

Anyone want to discuss dampening ballistic waves or shock pulses for a chuckle?

 

Are our crankshafts forged or cast? Anyone know?

 

Oh! Oh! Oh! I know! How about substituting dampening with shock reflection by large thermal gradients! Fly a Concord over L.A. or a SR-71 over Moscow with no sonic boom!