RB25 pulleys

[Steve]

the phantom, do you believe there would be benefit from replacing the other pulleys on the engine? v's negative effects?

[GTS-t VSPEC]

Yeah, ignoring changing the harmonic balancer for the time being, is it worth doing the others pulleys lightened?

[R31Nismoid]

i 3rd that motion...

I'm not worried aobut the harmonic one... just the other pulleys there that as rev said, being made lighter would make overall load less and spinning easier ???

[rev210]

Originally posted by the phantom

Hey rev210,

I disagree with you on a  number of points. The sole source of  the torsional excitation is from the impulses of combustion. The haramonic balancer is a driven device, and through its inertia is only a store of rotational energy delivered by the crank. As such it can not generate any excitation whatsoever, unless of course it is in a state of dynamic imbalance, which it is not. Weight of the balancer has nothing to do with excitation. Simply put a lighter balancer will have a lower ability to attenuate torsional vibration.

The OEM type balancer is significantly more expensive to manufacture than alternatives with its multiple sections/compositions and assembly. In many circumstances the balancer itself needs to be dynamically balanced as the outer ring cannot be positioned with total accuracy over the flexible rubber hub interface.

I think we are getting the pulleys confused with the harmonic dampers found on some V6 / V8 engines. "Harmonic Balancer" is a term that is used loosely in the automotive industry. Technically, this type of device does not exist. The "balancer" part comes from engines that are externally balanced and have a counterweight cast into the damper, hence the merging of the two terms. None of the applications that we are talking about utilize a counterweight as part of the pulley as these engines are internally balanced.

The pulleys on most of the new import and smaller domestic engines have an elastomer (rubber ring) incorporated into the pulley that looks similar to a harmonic damper. The elastomer in the OEM pulley serves as an isolator, which is there to suppress natural vibration and noise from the engine itself, the A/C compressor, P/S pump, and alternator. This is what the manufacturers call NVH (Noise Vibration & Harshness) when referring to noticeable noise and vibration in the passenger compartment. It is important to note that in these applications, this elastomer is somewhat inadequate in size, as well as life span, to act as an effective torsional damper. If you look at the pulleys on some of the imports there is no rubber to be found at all. Most who have installed and driven a vehicle with pulleys will notice the engine actually feels smoother. This is a natural result of replacing the heavy steel crank pulley with a CNC-machined aluminum pulley. NVH is variable and unique to every car. NVH will increase with the installation of an aftermarket intake and/or exhaust, for example. Think of OEM intake systems in newer cars, they use baffles and resonators in the intake to quiet all the intake noise. Aftermarket intakes eliminate these resonators and create dramatic increases in engine noise from the throttle opening and closing. So to most tuners, certain types of NVH can make the driving experience more enjoyable.

The purpose of a traditional harmonic damper is to protect against crank failure from torsional movement. This is not necessary in most modern engines because of the many advances in engine design and materials. Factors such as stroke, displacement, inline, V configurations, power output, etc., do determine when and how these harmonics and torsional movements occur.

Again, there is a lot of internet hearsay about the pulleys. When motor failures occur, too often people are quick to blame the pulley first, rather than taking the time to look logically into why there was a problem.

Here's a few examples of successful front pulley change overs on 6 cyl:

BMW M series , 5 series, Audi A6 ,Toyota the whole range of 6's found in supras including NA's and turbo's. This is a small sample of the straight 6's that can live without the harmonic balancer. All have had the front pulley replacement and none have had premature bearing failure as a direct result.

Food for thought.

[the phantom]

Hey rev210,

Your are absolutely right in making a note of the misnomer in "harmonic balancer". I'll try to be consistant from now on and call it a harmonic damper. Indeed none of this argument applies to this form of device, only to devices with a central hub and outer ring and/or pulley seperated by an elastomer material, for internally balanced engines.

I remain unconvinced that a rubberised "pulley" has a significant effect on NVH levels as a result of accesories. Connecting all the engine driven accesories is a very soft, pliable and flexible rubber belt. Very little if any vibration can get transmitted through this by the accesories to the engine or vice versa. In effect it does a wonderful job of isolating vibrations on its own. Such a rubberised pulley as described constitutes a harmonic dampener. Sure it may look different and small but that is a result of it being tuned for the engine under consideration. I agree that modern techniques and materials have altered the dynamics of torsional vibration such that the crankhaft is a much stiffer item than that of yesteryear.

This forum is about Skylines however, and all RB's I have ever seen have a more traditional harmonic balancer OEM mounted on the front of the crank, presumably for torsional issues present in this particular design. And if it could be reliably replaced to OEM standards with a much cheaper/smaller/easier to mass produce plain pulley, in my opinion, it would have. It is far cheaper to stamp a pulley out of sheet steel in a press or cast one out of aluminium than it is to make a two or more piece steel device with a rubber insert. Something else has undeniably been considered here.

My opinion on the other questions by Steve/GTS-t VSPEC/R31Nismoid regarding lighter pulleys on the other accessories is thus. Consider first the alternator. You could make a lighter pulley for it......but. Dont forget the rotating inertia of the alternator rotor. Being a big iron/copper component it outweighs its standard drive pulley by orders of magnitude and is of considerably larger radius. A lighter pulley here would have negligible effect. The water pump pulley doesn't weigh much at all. The power steering pulley is similarly light weight, and I would argue the same for that as the alternator. The AC compressor is probably too hard for anyone to consider modifying a pulley to suit, and for performance use one simply has to turn of the AC and remove all load.

What about making the pulleys larger so as to reduce the drive ratio and hence the load? Well doing that will also reduce your power steering pressure and your water pump and alternator speed. Water pump cavitation issues I believe will become significant enough at super high RPM to warrant consideration, but thats about it.

Consider the following example which I believe will suprise and hopefully enlighten a few people:

Calculate the power required to accelerate a rotating mass from 650 rpm to 7000 rpm in 2 seconds. Assume that the mass is all concentrated at the circumference, i.e a circular ring (pretty much equivalent to a pulley/damper, and worst case scenario, a solid disk has half the inertia), and that it weighs 5 kg, and has a diameter of 150mm.

The equation of power in watts for this is:

Power P = I x A x W ( "Power P = I times A times W")

where:

I = moment of inertia = MxR^^2 (mass times radius squared)

= 5 x 0.075 x 0.075

= 0.028125

A = angular acceleration in radians/second/second

= (7000- 650)/2

= 3175rpm per second

= 53 revs/second/second

= 53 x 2 x Pi

= 333 radians/second/second

W= angular speed in radians/second

= (650rpm / 60) x 2 x Pi

= 68 radians per second

inserting into the first equation.....

P = 0.028125 x 333 x 68

= 637 Watts

= 0.6 kW !!!!!

Not much to worry about is it. And this is for the heaviest part being the crank damper. Its probably not even measurable unless your in a lab on a very good engine dyno. If you spend the money to lighten it all how much would you expect to gain...if your really really good you might gain 0.4 kW during your acceleration!!! IMHO there are better and smarter ways to spend your performance dollar.

[EnricoPalazzo]

Thats very very interesting Phanton, however I believe the sole purpose of considering the lightened pullies was not to gain Hp but to allow the engine to rev quicker.

[Steve]

Give Enrico a cigar - hit the nail on the head.

If there were no benefit, why bother lightening the flywheel. Also all the trouble companies go to developing lightweight wheels would be wasted, and switching off your air con would do bugger all.

Peak hp figure only wins competitions on dynos, not on roads:)

thanks for the physics lessons though, quite interesting. Do you have any formulas that could be applied to accelleration?

[Steve]

Here is another thought, what effect would moving the greater part of the mass of the harmonic dampener to the centre of the wheel?

Would it still be able to dampen harmonics as effectively? or is this reliant on where the mass of the wheel is located relative to the centre?

[the phantom]

Yeah OK Enrico, point taken...I concede that the example did stray from the original point, that being acceleration response rather than power and therfore not entirely relevant to the issues that have come up on this thread. I'll try to come up with some equations and examples to quantify response as well. The important issue regarding flywheels is that inertia is related to radius squared, and with a flywheel being significantly heavier but more importantly much larger in radius the effect is considerably more significant. This also applies to Steves question regarding the positioning of the weight. I shall return...

[rev210]

the RB motors are NVH's not balancers. Hence the internal balance of the engine is super critical. So in this situation we are cool.

[GTS-t VSPEC]

Ok, anyone want to fill me in on what the plan is. Do we still look at getting the pulley's lightened, ignoring the harmonic damper. Do they retain the same dimensions, or do we make some larger/smaller?

[Steve]

Just wind up the boost:D

[rev210]

Paul make them the same size for now. As long as they are lighter thats what we really want.

[GTS-t VSPEC]

Dave, Ok, I'll try and borrow some stock ones for them to copy off:D

[51jay]

been an interesting discussion. I've always thought that changing the pulley sizes was to help stop the water pump from over revving at high engine speeds which causes cavitation and inefficient cooling

[the phantom]

Having given the comments that followed my last post some more thought, I have formulated an alternative argument that can be applied to the previous calculation example. In hindsight, it isn't that far off what we are discussing after all. Bear with me....

Consider two 'ideal' Skylines. Everything is EXACTLY the same, except one runs 5 PSI of boost and the other 10 PSI. They are both rolling at 60 kph in third. On a signal both cars have the throttle cracked open simultaneously. Which one will hit the redline first? I would suggest the 10 PSI Skyline, because it has more power (and mathematically proportional torque). Put enough weight in the boot however and the other will redline first. In essence the engines predisposition to rev is limited by the weight it has to lug through all the gearing, given no tyre slip. Increase the power some more and you will negate the additional weight in the boot. Remove some rotating mass and the power that was absorbed by the rotation becomes available to the tyres to help accelerate the vehicle at a greater rate, and thus through all the gearing, also allow the engine to accelerate at a faster rate. In essence, making it feel more responsive.

Rotating mass is thus equivalent to static mass that is present in the vehicle. The only difference being that it's effect is variable and determined by the gearing at the time. So the 0.6 kW that went into accelerating the dampener is now available to the wheels instead.

Which brings me once again back to the example. The power absorbed by the heaviest of all 'pulleys' the damper, amounts to a miniscule amount. Furthermore the alternator pulley that probably only weighs a few hundred grams becomes even more insignificant. Remember that the inertia of the alternator rotor is FAR FAR greater than the pulley its connected to anyway. The other pulleys again weigh bugger all so the argument is the same. The weight of the water moved by the pump and the heavy pulley mounting flange on the pump under the pulley, again makes it rather insignificant. The power steering pump, with its complex vane arrangement and so forth...surely more significant in rotaing weight and hydraulic losses than its driving pulley.

And what about lightweight flywheels. Using the previous example, and remembering that a 'flat disk' is more appropriate for the flywheel inertia, meaning that the inertia effect is halved, plugging in all the values for an 11kg flywheel, with all else being the same, amounts to almost 3kW. Significantly more than all the pulleys, and about 5 times more than the damper in the example. Also far easier and cheaper to perform. Yes lightweight flywheels are marketed by all the big name houses. And they all promise the earth....they are also trying to sell you something. Something made on a CNC machine that costs almost nothing. But is a lightweight flywheel included in the standard 'roady' upgrade list of "exhaust-intake-FMIC-ECU"....not really. If in fact it was so miraculous, every man and his dog would be rushing out to buy one and take advantage of the 'huge' benefits for the relative poultry sum of 500 bucks.

I tend to agree with Steve...up the boost a tad and the effect will be the same!!!

Every one of us however is entitled to our own opinion. I dont wish to hinder anyones ideas and plans. This is all just one mans take on the situation that I wish to share for the sake of discussion. I hope to hear the result of the lightweight pulleys the other guys are having made....backed up by test results of coarse )...and be proved way off the mark.

I also want to add more to the contentious issue of the damper/NVH "device". I took one off a spare RB25DET I have lying around to take a closer look. It is actually a more complex component than first thought. It is a three piece device, with two sets of elastomer linings. The inner hub connects to the crank snout and protrudes outwards forming the outermost pulley for the power steering pump. The inner belt lip of this pulley bends back toward the crank forming an open ended cylinder around the central hub. On the outside of the cylinder is a rubber lining which carries the AC and alternator/waterpump belt pulleys. On the inside of this cylinder however is a heavy metal ring that is held by the other rubber lining on the inside of the cylinder. The inner radius of this ring is floating in air and doesn't touch the central hub. Also of interest where the 3 balancing holes on the back of the innermost pulley as a result of dynamic balancing. In my personal opinion this constitutes a harmonic damper. Even though I dont believe that the outer lining is for NVH purposes due to the rubber accesory belts anyway as mentioned previously, if I assume it is, then the inner ring most certainly forms a harmonic dampening device. It is a typical example of such a thing, albeit on the inside rather than the outside. I also looked at an RB30 damper and discovered that it is different in construction although similar in principle. As I only studied this breifly, the major points of note were that it had a similar central hub but this time holding all the pulleys. There was a lone thin disk however on the inside edge that had the typical rubber lining seperating it from the hub.

On the point of crankshaft balancing, the inline 6 configuration is inherantly extremely well balanced and vibration free. All primary and secondary inertia forces and moments can be completely eliminated through balancing and couterweights alone. The only exictation present is through combustion impulses which leads to torsional vibration compounded by crankshaft length. This is opposed to the inline 4 for example which cannot achieve cancellation of secondary vertical shake through balancing and counterweighting and is usually, but not always, addressed by using counter balance shafts.

[DESCR8]

Phantom: My engine builder doesnt like Fluid Dampers such as the ATI items, he is big in the V8 market and doesnt believe in them would you think it would be wise to tell him i want one i will be spinning an RB30DET to 7,500-8,000 rpm and hoping for alot of HP (read more than 700)

Jordan

[the phantom]

Hey DESCR8,

I was under the impression that ATI dampers are a twin ring elastomer type af damper. According to their website actually. They have some good info there. The only fluid type damper I know of is the "Fluidampr" marketed by another American company. I am also building another RB30DET although not as intense as yours, just as intense as I can go still keeping it daily driveable...read reasonable engine lifetime. I've done a lot of research on fluid type dampeners and I personally am looking into using one although I'm not yet sure if I really need to...I dont plan to go past 7000. Many others have mentioned some bad harmonics on RB30's past 7500 odd...I'm still trying to find out more on this. Lots of different sources claim good properties from fluid dampers but as usual there are a few that dont like them. What reason does your engine builder give you for not liking fluid dampers??? Curious to know his opinion.

Have you seen the Autospeed and Zoom articles on the mega RB30 Nizpro in Melbourne built...900 odd horsepower from memory. They went to the trouble of making a huge solid one piece main cap/brace that bolted to all the sump bolts, and, modified a GTR 4wd sump...for added stiffness presumably. If you spot the Autospeed article, note the balancer used. It looks like an RB30 unit but with a much enlarged ring....hope this is of some use to you....

[rev210]

Phantom (the),

I guess the world of real race cars escapes your notice , I think you will find all bar none use a light flywheel (actually a very light one).Turn your calcualtions to inertia in 1st gear, and how this effects accelleration, you'll see what I mean.

[Sydneykid]

Hi guys, very interesting thread. Not a lot to add, except we find noticeable improvements in acceleration from making everything that goes up & down and round & round lighter. That includes wheels, heavens some of them are so heavy it's like having 4 flywheels.

Hi ghost who walks, harmonics is a very interesting subject it always makes my brain hurt. Since you brought it up, how about we debate "overbalancing" an RB30 so that the hamonic vibration is at 3,750 rpm instead of 7,500 rpm? That way you can rev it to 9,000 rpm with harmonics being an issue.

For anyone who is interested, I think Simon charges about $3K for the RB30 billett crank girdle that Mr Walker mentioned above.

See, I do really read Phantom comics.......