UDP theory
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From: Houston, TX
UDP theory
Could someone explain how an underdrive pulley works? I understand that they reduce the belt drag caused by my accessories, but I'd like a little more information. Will an UDP bypass my accessories entirely? I can't imagine that it would completely disable my alternator and water pump...
Last edited by verhagem; May 15, 2010 at 03:08 PM.
R.I.P. Dusty (Retired Moderator
Joined: Dec 2003
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From: Alamosa, Colorado (200 yards from the Rio Grande)
RE: UDP theory
They turn the alt and water pump slower thus using less power. They are also lighter than stock, saving a small bit of weight. Personally, I have no interest in them, the HP gain is too small for the cost and potential problems.
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RE: UDP theory
What potential problems?
All the potential problems you hear about are due to incorrect install and because there were problems there to begin with. With an UDP you gain 8hp that was there to begin with but was lost due to it's weight and the accessories it was driving. Granted, the gain is minimal, but it's still 8 HP that you weren't putting to good use. That was lost.
If you run a lot of extra accessories, like a stereo, lights things of that nature you may get a battery light. But it's generally not a big deal and you can get an ODP (Overdrive Pulley) for the alternator to correct that.
I've used a UDP for over 3 years and have never had an issue. I also have an ODP however, it's been in my center console for over 3 years. I've never installed it. I've only heard of a select few who had problems but like I said before, it was because the UDP's were installed incorrectly and they had electrical problems to begin with.
Here's the definition of Harmonic Balancer, Harmonic balancer: The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that's causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.
When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.
The Neon HB doesn't do quite the same thing as a true HB. The factory pulleys on today's late model cars (from 1986 to Present and sometimes even earlier depending on the vehicle) serve two functions. First and most importantly they are designed to reduce or eliminate the audible noises heard in the cabin of the car that the accessories (alternator, air conditioning, power steering, and air pump) make when the engine is running. This fact exhibits the factory fanaticism about making the car quiet for the occupants (i.e. the use of resonators in the intake to quiet intake noise, all aftermarket intakes eliminate these resonators). It has nothing to do with engine function or longevity.
All the potential problems you hear about are due to incorrect install and because there were problems there to begin with. With an UDP you gain 8hp that was there to begin with but was lost due to it's weight and the accessories it was driving. Granted, the gain is minimal, but it's still 8 HP that you weren't putting to good use. That was lost.
If you run a lot of extra accessories, like a stereo, lights things of that nature you may get a battery light. But it's generally not a big deal and you can get an ODP (Overdrive Pulley) for the alternator to correct that.
I've used a UDP for over 3 years and have never had an issue. I also have an ODP however, it's been in my center console for over 3 years. I've never installed it. I've only heard of a select few who had problems but like I said before, it was because the UDP's were installed incorrectly and they had electrical problems to begin with.
Here's the definition of Harmonic Balancer, Harmonic balancer: The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that's causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both.
When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.
The Neon HB doesn't do quite the same thing as a true HB. The factory pulleys on today's late model cars (from 1986 to Present and sometimes even earlier depending on the vehicle) serve two functions. First and most importantly they are designed to reduce or eliminate the audible noises heard in the cabin of the car that the accessories (alternator, air conditioning, power steering, and air pump) make when the engine is running. This fact exhibits the factory fanaticism about making the car quiet for the occupants (i.e. the use of resonators in the intake to quiet intake noise, all aftermarket intakes eliminate these resonators). It has nothing to do with engine function or longevity.
R.I.P. Dusty (Retired Moderator
Joined: Dec 2003
Posts: 24,471
Likes: 0
From: Alamosa, Colorado (200 yards from the Rio Grande)
RE: UDP theory
ORIGINAL: Crazy Squee
What potential problems?
All the potential problems you hear about are due to incorrect install and because there were problems there to begin with.
What potential problems?
All the potential problems you hear about are due to incorrect install and because there were problems there to begin with.
I would never put one on my SRT-4 since that puppy already runs hotter than a Texas BBQ!!!
I'm glad to hear it's working for you!!!![sm=icon_cheers.gif][sm=icon_rock.gif]
R.I.P. Dusty (Retired Moderator
Joined: Dec 2003
Posts: 24,471
Likes: 0
From: Alamosa, Colorado (200 yards from the Rio Grande)
RE: UDP theory
Good question. Modern Performance sells them, but I've never really checked into it. Now I have some research to do!!!
