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Discussion Starter #1
I just found this Site and saw they had underdrive pulleys among a couple other things. Are they worth it? I haven't heard anyoe talking about them so I was just wondering. Seems like there are other things I'm going to spend my $$ on first.

Jeff
 

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I personally have never been a fan of underdrive pulleys. Unless you have no intention of running full power from your alternator, A/C, etc. and you have a more than adequate cooling system (bigger radiator and ducting) they are a waste of money. They put a lot of wear on your accessories and are not worth the measly gains. Especially when upping the boost with a $50.00 manual boost controller 1psi will double the gains you can get with that $500.00 kit.
 

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With a turboed engine an Underdrive pulley will not benefit you. In fact it could ruin you


Pulleys are normally good for NA engines
 

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Kinda what I figured. I've never liked the idea of running the accessories slower either, just doesn't seem like a good idea in most cases. Besides, a little bit more would get you a DP :D
 

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With a turboed engine an Underdrive pulley will not benefit you. In fact it could ruin you
Pulleys are normally good for NA engines
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Nope, they aren't good for ANY engine, period.. They suck, plain as that.

My other car spins 10k rpms without any bottom end mods and has been doing it for 2 years as a daily driver while others throw rods at 7k rpms after only a month. Its because they have UDPs, and I do NOT.

The engine is balanced with the stock pulley, you take that away and the vibrations from the crank end will wear out all the parts nearest the pulley side: rod bearing, mains, and your oil pump on a normal motor.

We have a seperated oil pump, so that would survive but your rod and mains wouldn't.

Seriously, lightened UDPs should be completely ignored. Many engine builders won't put them on if you bring them in when setting up a motor.
 

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ever seen a crankshaft snap in half? I have many times with cars with under drive crank pullies
 

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I read that aluminum lightweight pulleys, underdrive or not, adversely affect the motor because the do not have a harmonic dampener. Not really sure what that is other than a fancy name for a big heavy chunk of steel but didn't want to take a chance after reading it. I did have one on a 2000 Legacy GT and did notice quite a difference in acceleration. I think there are much better (safer) options for gains. My .02
 

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I read that aluminum lightweight pulleys, underdrive or not, adversely affect the motor because the do not have a harmonic dampener. Not really sure what that is other than a fancy name for a big heavy chunk of steel but didn't want to take a chance after reading it. I did have one on a 2000 Legacy GT and did notice quite a difference in acceleration. I think there are much better (safer) options for gains. My .02
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From Wikipedia

This potentially damaging harmonic vibration can be controlled by a vibration damper - which is also called a torsional damper, harmonic damper, or erroneously a "harmonic balancer". The main purpose of a "harmonic damper" is to control harmonic vibration, not necessarily to balance the engine's rotating assembly.
 

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WOW! Its astonishing how much bad information is in this thread. To say that an underdrive pulley would wear out your accessories couldn't be further from the truth. In reality, they reduce the wear on them because they spin slower. Most UD pulleys only reduce the speed of the accessories a modest amount (20%) and this will have NO effect on your charging system. Once your car reaches about 1500 rpm, your alternator is at maximium output.


Its also incorrect to say they don't work on turbo cars. They offer the same improvements on any car, regardless of turbo or not.
 

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^^ +1
 

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Once your car reaches about 1500 rpm, your alternator is at maximium output.
Its also incorrect to say they don't work on turbo cars. They offer the same improvements on any car, regardless of turbo or not.
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Wow, its amazing how many people come on here and say WOW! ;)

You can look at some of the SAE testing if you think that a lightened udp pulley is a good idea. There has been volumes of testing using sensitive microphones to test the vibrations and harmonics on the crank at various rpms , over and over, and the information is clear: a UDP is not heavy enough to absorb the vibrations on the crank end and you will lose bearings and oilpumps for a few extra hp.

Therefore, its NOT an improvement. You want hp, you port the heads, change the intake, increase the boost, put on a better IC, etc, but you DON'T change the endweight (pulley) on the crank!

And, yes, when you bring in a block to be spinbalanced to 10k+, they ask for the crank pulley and the flywheel to be mounted and they tell you up front NO ALLOY UDPs!

As a matter of fact, some UDPs fail and separate.

No way no how is this some sort of "improvement".

If you want to save weight, you can do alot more by changing all the pulleys EXCEPT the crank pulley.

Buy a set of power pulleys: underdriven alternator, power steering, waterpump, AC, and lightened tensioners and idlers. You will get way more gains by saving 6lbs off of all of those collectively rather than 3lbs off of the crank and risk damage.
 

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I know the 3.0 with pulleys had adverse effects due to the engine's "harmonic balancer" paired with our pulley...AKA Ford's Dual Mass Dampener. I don;t know if that holds true with the MS6 as well (obvious engine differences V6/4T), but both in tune seem to be(but not in every case) very necessary to my engine. Just making an observatory comment. I could be wrong about theMS6, but it definitely begs to be researched.
 

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The idea of an underdrive pulley is simply to return back to the engine some of the parasitic loss associated with turning accessories.

Bad information? Yes...there is a lot here!

Your engine accessories work within a range of RPM's. Your alternator also has a "coming in speed" where it begins to creat voltage. As the RPM's increase so does amp output...to a point. At some point well below max RPM, and slightly below normal cruise RPM it is at max amps.
So by using an underdrive pulley you simply shift the max output up a few hundred RPM.

The loss from spinning the alternator and such is exponentially greater with RPM's. Lower the RPM's you spin the accessories and you lower the loss associated at any given RPM. True...you do not want to underdrive things too far. But normal underdrive pulleys will not negatively effect most folks at all.

A harmonic ballancer is not a pulley, unless it is an integral ballancer/pulley. I do not know if our car has a ballancer with a pulley valley machined into it or not....but if it did...there would not be an underdrive pulley for the crankshaft.

As a crankshaft takes the hit from the power stroke, it twistes and resonates in a torsional plane. The harmonic dampener works like a shock absorber for this and dampens down the twist by allowing the dampener to resonate by absorbing the frequency of the crankshaft.

A crankshaft that is left to go into harmonics will experiance premature bearing wear and possable mechanical failure. Its not a good thing.

If a underdrive pulley were out of ballance to begin with and you installed it on a rotating assembly that was not ballanced with it installed you would insight vibration and cause failure eventually.....sooner or later the material of the crank would say "I have had enough..." and it would fail.

Is an underdrive pulley going to return to you a few HP...? Yes. The higher the RPM rang you go into, the more an underdrive pulley will give you back. The guy above going 10K RPM would see larger gains on a dyno than a guy with a 455 Buik that redlines at 5500 RPM.

Could it be damaging....sure....if things are not manufactured properly and you create a ballance issue where there was not one before.

The accessories driven off of the crankshaft are all leeches, taking HP to overcome mechanical resistance. Is it easier for you to walk while holding a Bowling-ball...or is it easier to run while holding it? Similar situation on your accessories.....it takes more energy to spin them faster, and you get more resistance as RPM's increase. Decrease the RPM's you spin them, and decrease the energy absorbed by them.

On my Ford sled pulling engine I was exploding alternators about every 7-10 20 second runs. At the RPM range I was in the alternator bearings were swelling, seizing, and causing the rotor to seize and shatter the housing. I went to a Moroso crank pulley that is 2.5" smaller in diameter, and I went with a Moroso alternator pulley that is 2" larger in diameter and I have used the same alternator for 2 years now with no failure.

On a basic street car that is mostly stock like most of these cars, looking to drop $300-$500 un a pulley that may get you back 5-10 HP at max operating RPM does not sound logical. For a race car or like me....a sled pulling truck that is operating within a set of rules that limits you to the point that you are looking for that last 2 HP to edge out the competition...it is worth it. If you blowing apart $200 alternators every week or three...sure its worth it.

I offer you some information, you can read it and make up your own mind. I will not tell you waht to do.

Merry CHRISTmas guys!!!!
 
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