Just wanted to see if anybody had some input on this subject. I have been wanting to install some sort of lightweight pulley on my crank to compliment my lightweight flywheel on my KA'd S14. I have seen most of the ones that are available are called "Crank Pulley" or "Underdrive Pulley". A friend of mine that is totally obsessed with Mustangs is telling me that this in fact is not just a pulley but also a balancer that should be balanced with the whole rotating assembly. He says that using some off the shelf lightweight pulley is designed for race applications only. Is this true? Does this only pertain to V8's? He also is saying this could lead to oil pump failure, and in severe cases excessive motor vibration. He also worned of my lightweight flywheel causing problems to but I haven't had a single one, except may be running out of RPM's faster...

The stock crank pulley absorbs some of the vibrations in the crank, which is good.
Solid aluminum ones don't absorb vibrations in the crank, which is not so good.

I'd stick with the stock pulley, find power elsewhere.

well they are also called harmonic balancers. and harmonics can snap your crank shaft. there is a company that makes aftermarket ones for the ka, but they arent lighter i dont think. pretty sure they just take out the harmonics better.

Never seen problems with them though. I've been running an alum crank pulley for 7+ years.

biggie wrote:Never seen problems with them though. I've been running an alum crank pulley for 7+ years.

I dont recall how long, its been but IIRC it was even on my sohc but its also not an ebay pulley.

for the record if it was going to snap off due to harmonics, it would have happen long ago. They are a half counter weighted motor, big part of not making over 200whp in na form.

Thanks everyone. Razi, have you had problems with an aluminum pulley before? Do you know someone who has had problems?

So far doesn't seem like anyone has had any problems so I'm gonna give it a try when I put my car under the knife to install my turbo set up I've been puttin together. Should go nicely with my lightweight flywheel and the new accessory pulley set I picked up a while ago.

There have been a few times I've seen people that had weird vibrations problems from the pulleys.
I think keeping the stock pulley would be a good idea, you won't feel much of a gain from the aluminum one anyways.

Razi wrote:There have been a few times I've seen people that had weird vibrations problems from the pulleys.
I think keeping the stock pulley would be a good idea, you won't feel much of a gain from the aluminum one anyways.

negative.
maybe ebay pulley?

maybe not noticable boosted, but before I was boosted I had the pulley and it had way more pep to the revs. I need mine, if I added back that 9pounds to my drivetrain I could make full boost out of gear(making 5 now) without the planned launch control. spark cut only, hope the car holds together

Yeah I had an Unorthodox aluminum pulley on for 7-8 years with no problems. But all of those years were N/A.

We ran the Unorthodox pulley on the Pikes Peak car in 2009 and didn't have any trouble with it (revving to 7000+ pretty regularly). For grins we swapped in the ATI damper and although it does rev just slightly slower the rev out is notcieably smoother. In both situations we ran 16-20psi boost. With the ATI we were also just slightly down on hp, but the longevity we will gain with the improved hamonics dampening we feel will be worth it (in the long run).
The Unorthodox pulley is a trick piece for sure, but I think it's better suited to an NA motor seeing race duty. For everyday use (and in my race car) I think the ATI damper is the way to go.

great info! ^^ do either of the pulleys have marks for the ignition timing?

I know the Unorthodox does for sure.

ss82480 wrote:I know the Unorthodox does for sure.

and the asp I have has them.

I knew fluidamp wasnt correct.

kenno470 wrote:We ran the Unorthodox pulley on the Pikes Peak car in 2009 and didn't have any trouble with it (revving to 7000+ pretty regularly). For grins we swapped in the ATI damper and although it does rev just slightly slower the rev out is notcieably smoother. In both situations we ran 16-20psi boost. With the ATI we were also just slightly down on hp, but the longevity we will gain with the improved hamonics dampening we feel will be worth it (in the long run).
The Unorthodox pulley is a trick piece for sure, but I think it's better suited to an NA motor seeing race duty. For everyday use (and in my race car) I think the ATI damper is the way to go.

Great post. Yes you can run an aluminum crank pulley, but any chance you get to remove a vibration should be taken.

Just a quick explanation of how a harmonic balancer actually works, since no one seems to have mentioned it yet... If you look closely at a stock crank pulley, you'll notice that its actually a center steel hub section joined to a separate outer steel ring by a thin ring of hard rubber. This allows the outer ring to move slightly separately from the inner section, due to the slight flexibility in the rubber. Why is this necessary? Because in an internal combustion engine, every time a power stroke occurs on one of the cylinders, the crankshaft accelerates very slightly, and on every compression stroke, the crankshaft decelerates slightly, of course these accelerations and decelerations are extremely brief and happen hundreds of times a second, so they will all blend together when observed with the naked eye. This is where the harmonic balancer comes in; when the crankshaft accelerates on a power stroke, the inertia of the heavy outer ring keeps it from accelerating at quite the same rate as the inner hub, as rubber between the sections flexes. This opposes the force of the acceleration and dampens the shock of the power stroke. Vice versa on compression strokes, the crankshaft and inner section of the pulley slow down, but the inertia of the outer ring provides the opposing force to this deceleration, dampening the shock of the compression stroke. This whole process happens, as I said, hundreds of times a second. This dampens harmonic vibrations that, if left unchecked, can weaken the crankshaft over time. Sorry if this post is a bit convoluted, I did my best, but its kind of an abstract concept. Now I realize why no one's gone to the trouble to explain it thus far

SX APPEAL wrote:Just a quick explanation of how a harmonic balancer actually works, since no one seems to have mentioned it yet... If you look closely at a stock crank pulley, you'll notice that its actually a center steel hub section joined to a separate outer steel ring by a thin ring of hard rubber. This allows the outer ring to move slightly separately from the inner section, due to the slight flexibility in the rubber. Why is this necessary? Because in an internal combustion engine, every time a power stroke occurs on one of the cylinders, the crankshaft accelerates very slightly, and on every compression stroke, the crankshaft decelerates slightly, of course these accelerations and decelerations are extremely brief and happen hundreds of times a second, so they will all blend together when observed with the naked eye. This is where the harmonic balancer comes in; when the crankshaft accelerates on a power stroke, the inertia of the heavy outer ring keeps it from accelerating at quite the same rate as the inner hub, as rubber between the sections flexes. This opposes the force of the acceleration and dampens the shock of the power stroke. Vice versa on compression strokes, the crankshaft and inner section of the pulley slow down, but the inertia of the outer ring provides the opposing force to this deceleration, dampening the shock of the compression stroke. This whole process happens, as I said, hundreds of times a second. This dampens harmonic vibrations that, if left unchecked, can weaken the crankshaft over time. Sorry if this post is a bit convoluted, I did my best, but its kind of an abstract concept. Now I realize why no one's gone to the trouble to explain it thus far

Almost, but it seems you have missed the actual point of this device, which is to dampen TORSIONAL vibrations, not the dynamic imbalance caused by the accel/decel of the crank pins. Torsional vibrations come from the flexibility of the crank pin arms on the crankshaft. They bend (very SLIGHTLY) under load (power stroke), and when that load disappears (around BDC), and they become "free", they begin to swing/vibrate/bounce. Just as any spring, if compressed, then released quickly. The possible problem with this is, if the frequency of these vibrations (frequency ~ RPM) comes very near to the resonant frequency of the rotating assembly, the vibrations are going to stack up, amplifying themselves, until eventually, the amplitude of these vibrations, and thus, the stresses that they cause in the crankshaft become so high, that the crank breaks. (don't know the correct term for this phenomenon)
This is where the crank pulley/harmonic balancer/torsional damper comes in. The hard rubber+outer ring is tuned to absorb torsional vibrations of a specific frequency. The frequeny at which the vibrations tend to become the strongest, which is the resonant/natural frequency of the rotating assembly.
I would not replace the stock pulley with any solid part, that has no measures in place to reduce these vibrations. From what I understand, you can get away without one on an all out race engine, as those do not spend too much time at one specific RPM, so there's no time for these runaway vibrations to build up.
Recommended read (basically the whole site): http://www.epi-eng.com/piston_engine_te ... orbers.htm
I've found some of the articles incredibly enlightening.

hmmm... "I see!" said the blind man, hahaha.

So its not the accel/decel of the crank itself thats being dampened, but the vibrations in the crank caused by the force of the power strokes, which are the accel force. I think I was pretty close, but thanks for the education!

Great thread guys, I think I'll make it into an article for the tech page.

alright I love when threads get all deep.

quick question. I have a white bunny clutch setup(extremely heavy) ,would I be gaining from going back to the stock pulley(adding another ten pounds back to the rotating assembly)?
I dont recall the exact numbers I got but the WB clutch outweighed the stock type clutch setup by some 15lbs. I felt using an asp was needed to bring the weight back down. Maybe its less help, but I think I would really hurt revs adding back 10lbs?
input?

I mean swapping back to the stock crank pulley is cake, I have to take this motor out again...

Wow I'm glad I started this post. I first thought that it might be considered a dumb question, or get no response. Thanks for all the information gentlemen, didn't realize when I asked this question that WD would one day permanently put it in the tech pages.

neverlift wrote:alright I love when threads get all deep.

quick question. I have a white bunny clutch setup(extremely heavy) ,would I be gaining from going back to the stock pulley(adding another ten pounds back to the rotating assembly)?
I dont recall the exact numbers I got but the WB clutch outweighed the stock type clutch setup by some 15lbs. I felt using an asp was needed to bring the weight back down. Maybe its less help, but I think I would really hurt revs adding back 10lbs?
input?

I mean swapping back to the stock crank pulley is cake, I have to take this motor out again...

As I said, I wouldn't even have gone to a completely solid pulley in the first place. The article linked above was convincing enough for me not to do so. But I guess to each their own. If you haven't snapped a crankshaft, or spun a bearing using this pulley for a long time, it might be OK in your application.

If you're asking whether you'll gain hp/tq, or a higher safe redline by putting back the stock pulley because of the reduced torsional vibrations, that I can't answer, but I'd be happy if someone could.
As for the crank pulley weight, I'm sure the upsides and downsides were already thoroughly dissected somewhere in this forum.
Lighter= you rev up quicker on acceleration, but also lose revs quicker on decel./gear changes, or sudden heavy loads (like driving into a slope). It has the same effect on engine response as if you made the car itself lighter.

WDRacing wrote:Great thread guys, I think I'll make it into an article for the tech page.

I think you should just post a link to the piston engine technology section of that webpage as a general sticky/recommended read. Maybe there would be less "8000rpm KA" threads over time, if people understood what happens in their engines at a slightly deeper level.

Running ASP pulley for 4 years with 7300rpm redline. My bearings seem to still be in good shape, no shavings in my oil.

the factors in question have absolutely nothing to do with bearing wear, but thanks for your input...

SX APPEAL wrote:the factors in question have absolutely nothing to do with bearing wear, but thanks for your input...

Actually, they have...
Some types of bearing wear can be symptoms of an out of balance rotating assembly.

Out of balance I can understand, but I can't quite figure out how harmonic vibrations in the crankshaft linear to its rotation can have any effect at all on the bearings. Please explain.

Btw sunny, don't take my drunk smartass post personally, wasn't trying to insinuate anything. I should really stop checking nico after getting home from the bar lol...