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 Aftermarket Underdrive Pully, will it Destroy Your Engine 
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Post Aftermarket Underdrive Pully, will it Destroy Your Engine
Ok, I punched the Search option three times and came up empty. Now we all know our engines are internally balanced, I'm not talking about that.
Every time the cylinders fire, torque is imparted to the crankshaft. The crankshaft deflects under this torque, which sets up vibrations when the torque is released. At certain engine speeds the torques imparted by the cylinders are in synch with the vibrations in the crankshaft, which results in a phenomenon called resonance. This resonance causes stress beyond what the crankshaft can withstand, resulting in crankshaft failure. Or at very least crank bearing damage.
Now I stole most of that from this page. http://www.d-series.org/forums/engine-b ... -read.html
My question is,,,,for a couple of HP MAX are we setting our engines up for an early failure by purchasing certain fashionable under drive pulleys cuz I for one see no benefit in them. Do certain JDM engines come with them installed from the factory?

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April 18 2011, 9:12 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
They are s---.

Harmonics are no joke, there are whole PhD's dedicated to vibrations and resonance, perhaps one to this subject alone. Ignoring this fact just shows that you don't want to hear the truth, or you're not smart enough to appreciate that engineering goes much beyond common sense(enough to sometimes be uncommon :P).

Don't waste your time, money, or peace of mind. UDP's will only overheat your engine, kill your alternator, cheap ones will fall apart and damage your oil pump,you'll wear out ALL your crank bearings faster, and risk catastrophic failure.

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April 18 2011, 9:21 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
Thanks Ryan
Ok, here's a big write up by Unorthodox Racing. http://www.unorthodoxracing.com/faq.aspx#section2
Now it's a good read but if an engine didn't need dampening why would manufacturers waste money installing them????? I have to think Mazda has better engineers than Unorthodox.
As a side note my engine has one of these damn pulleys and I can't find a timing mark. Like thanks a lot eh. I'll be removing it as soon as I complete about 6 other projects in my job jar.

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April 18 2011, 9:27 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
I'm not going to comment because there are some people on this forum that think they're so smart and can never be wrong so it really doesn't matter what is said because nothing will change. Having said that, for those looking to educate themselves on the topic, there is plenty of unbiased info on the net - just make sure you understand everything because it can get hard to follow and it's very relative (every engine is different and not everything applies the same way to every engine).

=)

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April 18 2011, 10:04 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
No it will not destroy your engine. I have run UDP's (underdrive Pulley's) on many vehicles. Honda's are externally balanced. They NEED the stock balancer or they run the risk of destroying the engine. It shouldn't over heat your engine if your cooling system is up to snuff. I don't understand how it will "kill your alternator" considering that the alternator will be spinning slower which is easier on the bearings. It wont put any extra stress on the brushes in the alternator it will still put out the same amperage, just at a slower speed.

On an internally balanced engine. It has similar affects as a light weight fly wheel.

I tow over 8000lb's with my truck and haven't had a problem with overheating while running UDP's. The only problem I have experienced is while in gear at idle the power steering is tight from the under driven pump.

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April 18 2011, 10:07 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
The problem with UDP's is that there's plenty of scientific evidence that relates to harmonics and vibrations and could/can directly apply, but there's no real hard evidence that UDP's are widely guilty of causing damage. There may be some, some that sure, it's possible, other cases may because by the UDP aggravating an existing problem that shouldn't be there to begin with, or just a problem that the UDP isn't guilty of, but there's no other major points to say otherwise.

My Mx-3 was going to (and I had it in my parts inventory) have one, and my Rx-8, although a totally different beast, will eventually get one. Although with my Mx-3, it was going to rev to or beyond 9000rpms with the planned motor, so it would of been a good things to slow down the accessories anyway.

To each their own, but my opinion is that there's plenty of evidence that can easily and strongly be applied to and against the UDP, but without any concrete trial and study evidence on a motor, especially on a Mazda K-series, there's no way to disprove the plausibility of the possible affect of resonance and vibrations that may or may not exist, or may or may not have been damped by a harmonic balance, on a motor. As mentioned, an aftermarket/lightweight flywheel should throw the motor out of whack just the same as an UDP if that was the case.

And as far as I'm aware of, I know of no such reports on this site that anyone has ever experienced a major problem/failure because of a UDP.

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April 18 2011, 10:51 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
The alternator will not fail mechanically (bearings) from running at low speed. If the alternator is not spinning fast enough, it cannot keep up with the draw on the system, and it will overheat and fry electrically. Also, alternators shouldn't get going too fast either... you have to choose that pulley ratio depending on your application.

I think Nd4SpdSe has this nailed down, and I think Night Shade should whip out some references instead of alluding. I don't mind arguing, and I'm not totally unreasonable, you just have to put a convincing argument not a "I'm probably smarter than you so ha". I just really hope my engineering degree doesn't constitute this "I'm smarter than you so nothing will change(from lies)" attitude, or I should probably just quit.

Changing the flywheel isn't as big a deal as the balancer, that will change some of the frequencies, perhaps reducing the effectiveness of the balancer, but its nowhere near the same effect as removing it entirely...

I don't suggest researching on a website that sells UDP's.

I suggest looking at the gains...

Inertia? Give me a break. Moment of inertia of a homogeneous disc is (pi r^4)/4 ... that is a function of the radius to the fourth. Since this thing is 6" in diameter, you WON'T see any inertial gains.

Underdriving the components is about the only place you'd see gains... from underdriving the W/P and P/S at high RPM. A/C is clutched and is an idler (unless you race with your A/C on) and the alternator is switched, so it doesn't put out more than it needs anyway (bigger alternator -> next to useless)

Also, an unorthadox UDP is $800 from their website... holy s--- I hope thats a typo. http://www.unorthodoxracing.com/searchp ... ategory=-1

I don't think even most of the minds on PT are brilliant, but this applies to our engines....

http://forums.probetalk.com/search.php?searchid=2167529

Experience shows the facts, science tries to explain it... who cares what reasoning you respect more.

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April 18 2011, 11:57 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
Jeez Ryan, I wasn't pointing fingers at anyone, especially you! But you know what they say, a guilty conscience needs no accuser :P

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April 19 2011, 12:44 AM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
Ryan wrote:
Changing the flywheel isn't as big a deal as the balancer, that will change some of the frequencies, perhaps reducing the effectiveness of the balancer, but its nowhere near the same effect as removing it entirely...


Removing the flywheel would be like removing your crank pulley. But for what I understand is that the harmonic balancer is suppose to counter-act the vibrations caused by the imprecision of the balance of the internal components, which would be in ounces, or even fractions there of. The flywheel, we shave off several pounds, almost 15 coming from a Probe/Mx6, that's a HUGE weight discrepancy on the crank system. You could say that the inertia of the heavy flywheel could damped the vibrations, but this would make things worse with mass removed from it. Maybe the UDP issue is in conjunction with a lightened flywheel, who knows...

Ryan wrote:
I don't suggest researching on a website that sells UDP's.

Biasness is in the eye of the article writer



Ryan wrote:
If the alternator is not spinning fast enough, it cannot keep up with the draw on the system, and it will overheat and fry electrically. [...] and the alternator is switched, so it doesn't put out more than it needs anyway (bigger alternator -> next to useless)


My truck currently has a marine alternator in it. It's a tad underdriven since I'll drop to 12v charging if I'm around and under 500rpms, but it does literally get submerged once in a while, so I'll do with that I can. It's also tested for 165amps, over the stock 90amp alternator, and this makes a HUGE difference when it comes to keeping power up when using my winch, which can draw up to 400amps, even with a Yellow Top. Normally it would struggle at the first use, but since, I've literally used several times in an afternoon (mostly pulling Jeeps out, lol!) and she kept up with me no problem

Ryan wrote:
I don't think even most of the minds on PT are brilliant, but this applies to our engines....

http://forums.probetalk.com/search.php?searchid=2167529

Quote:
Sorry - no matches. Please try some different terms.

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April 19 2011, 6:56 AM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
Nd4SpdSe wrote:
Removing the flywheel would be like removing your crank pulley. But for what I understand is that the harmonic balancer is suppose to counter-act the vibrations caused by the imprecision of the balance of the internal components, which would be in ounces, or even fractions there of. The flywheel, we shave off several pounds, almost 15 coming from a Probe/Mx6, that's a HUGE weight discrepancy on the crank system. You could say that the inertia of the heavy flywheel could damped the vibrations, but this would make things worse with mass removed from it. Maybe the UDP issue is in conjunction with a lightened flywheel, who knows...


I hope no one REMOVES their flywheel.... but I don't think that the balancer is designed to work against only rotational balance imperfections because these are factory engines... none of the balances are the same, and you've seen the harmonic balancer, its not exactly a precise thing. The pulse torque loads on the crank and the strain that produces, the lash between the components, as well as the non-axial vibrations caused by imbalance and said pulsating stress, the weight of the flywheel on the end being like the weight on an old metronome :)

Even my balancing shop isn't sure if the UDP is a good idea, even if I'm fully balancing my rotating assembly.




Nd4SpdSe wrote:
My truck currently has a marine alternator in it. It's a tad underdriven since I'll drop to 12v charging if I'm around and under 500rpms, but it does literally get submerged once in a while, so I'll do with that I can. It's also tested for 165amps, over the stock 90amp alternator, and this makes a HUGE difference when it comes to keeping power up when using my winch, which can draw up to 400amps, even with a Yellow Top. Normally it would struggle at the first use, but since, I've literally used several times in an afternoon (mostly pulling Jeeps out, lol!) and she kept up with me no problem


I honestly meant on stock systems. If you have a much higher draw then you for sure need a bigger alternator, may it be a big winch or a lot of stereo :) But you see that it still undercharges at low RPM... neato eh. (500 RPM -> 3:1 rule of thumb alty ratio -> 1500 RPM, and 2000 being a rule of thumb lower limit)


Just search "UDP" on PT. Lots of for and against... lots of experience with the quality of the cheap ones.

Night Shade, I just figured, since I seemed to be the only one with a strong opinion so far :P I still like to know if I'm wrong, though, so, by all means :).

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April 19 2011, 8:57 AM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
I think the flywheel issue is possibly a moot point. Automatics don't have one, they just have a round light weight wheel with teeth on the outer peripheral. So back to the UDP. Oh and by the way Igor is probably bias because he just bough an Unorthodox UDP. Red isn't it. :D
I think the issue of resonance is a pretty valid argument. I doubt you'll ever see crank failure being blamed on the UDP because identifying that as the cause wouldn't cross most peoples minds and if it did how would you identify that as the cause. Does this phenomena impart some kind of unique destructive wear pattern on the crank journals and if so you'd need to photograph and enlarge the picture to identify it. So this seems to come down to gains vs possible engine/crank failure. And Ya I saw that $800 dollar price, are they fu*king dreaming and who pays that for a stupid UDP? I guess rich single guys still living with their parents. :P

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April 19 2011, 8:27 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
My F150 has >390,000km (>240,000 miles). It is still on its original alternator. Half of the miles have been underdriven and with a 800 watt stereo. Which part of the alternator fries electrically? Brushes? Regulator? Stator?

harmonic balancer is an old term transfered over to newer technology. The harmonic balancer back in the day was used to balance out the rotating assembly and turn the accessories. it is not used on many applications any more to balance out the rotating assembly, its only purpose is to run the accessories.

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April 19 2011, 8:51 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
So since we have so many engineer types, how bout I throw this in the mix, Fluid dampners as replacements for UD pulleys...

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April 19 2011, 10:42 PM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
The underdriving is only an issue at low speeds. 300+k underdriven is fine if they're highway.

Killing the alty at low speeds... I'm not sure on this, but I figure since the output is low at low RPM, the alternator must be switched "on" for much longer periods of time, heating up the stator and rectifier, and coupled with the cooling fins travelling slower, it would eventually kill them.

If your underdriven alty puts out more than 12v at low idle, then I'd say you're good. You'd want more than that if you love to pound your bass at the stoplights, or do a low of low idle, high load work, like winching or powering a big inverter or a welder (some trucks do)

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April 20 2011, 12:10 AM
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Post Re: Aftermarket Underdrive Pully, will it Destroy Your Engin
It's nice to see some opinions put out there on a controversial topic, I don't think I've seen this discussion on this board before.

There are TONS of posts on PT both for and against UDPs, yet I've seen zero proof that the benefits or risks even exist... It sounds simple enough to reduce the size of the pulley and "free up" horsepower, but it's never that simple with cars. You aren't shifting to a lower gear on a bicycle... These things run a fair bit more torque(understatement). That being said, at the VERY LEAST, don't throw a $15 ebay UDP on your engine... If it's been engineered, as opposed to CNC'd and mass produced in China... you're at least decreasing your chances of a problem. That goes for anything you buy, in person, or online.

I'll probably never go this route, when I see so many more viable ways to gain or free up power... If I ever do, it'll be after finding concrete evidence(with supporting data of course) that shows it's not only safe, but worth the cost.)

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August 30 2011, 3:22 AM
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