The underdrive percentage AND the weight of the pulley determines the power difference.The consideration along with the dyno is how much it underdrives what it drives. I believe Dinan offers two different underdrive strengths, for example, with different performance levels. I would think that it's the amount of underdrive and not who makes the pulley that determines the power, so I would consider both factors together. There is obviously build quality and customer services issues in play.
ah, can you explain why that is?Just a reminder: as mentioned many times in this forum, eddy current braked dynos will not show power differences with drivetain weight/drag changes. This includes Mustang dynos and DynoDynamics dynos. Only inertial dynos measure that.
Lemme take a quick guess as to what kind of dyno that was measured on...
Loss of drivetrain weight doesn't really add power. Your engine is putting out the same amount as before. This is what an eddy current braked dyno is measuring.ah, can you explain why that is?
In terms of the performance, changes closer to the engine will make a bigger difference than further. So a smaller weight change in a pulley or flywheel will make a substantially bigger difference than changes in weight at the wheel or tire.Which provides the largest dynamic increase in performance,
2) Removing your valve stem caps?
I assume running well worn tires, or wheel balance weights removed would be a much larger increase than either.
Just a reminder: as mentioned many times in this forum, eddy current braked dynos will not show power differences with drivetain weight/drag changes. This includes Mustang dynos and DynoDynamics dynos. Only inertial dynos measure that.
Loss of drivetrain weight doesn't really add power. Your engine is putting out the same amount as before. This is what an eddy current braked dyno is measuring.
However, when you lose drivetrain weight (or more precisely, drag), your car will accelerate more quickly. An inertial braked dyno is measuring this accelerative force (you're basically turning a big heavy drum).
So does a pulley add power? No, not really. However, does it change your rate of acceleration in the same way adding power does? Yes, definitely.
Lighter wheels/tires have the same issue/effect. They allow you to accelerate faster, but do not add to your engine horsepower.
Your dyno operator should have explained that to you, and he did a disservice to you by not. Dynos are GREAT tools, but they're only that: tools. How they're used and how the information is presented to you really determines what you, as a customer, gets out of it.
I hope this helps!
On an eddy current dyno, you're measuring force directly. In that example, you're measuring the force it takes to stop that man pushing the shopping cart. When you lighten the lead jacket, the man can push the cart more easily, (and thus faster), but the force used to stop him will remain the same (mass lower, acceleration higher).Think of this like you (1 manpower) while wearing a jacket made of lead pushing a shopping cart full of bricks to a speed of 5mph. Now take the same man and same cart full of bricks but imagine that you ripped one sleeve of that lead jacket off thus lightening your personal load a bit. It will now take less time to push that same cart (aka load) to 5mph because more of your total power can be dedicated to just push the cart rather than carry the full weight of that heavy jacket too. Thus the acceleration is quicker. This is because even though the same amount of total force of 1 manpower is still present in both situations, some of it was already used in just moving forward with the lead jacket let alone accelerating the cart full of bricks to a given speed. Now replace the man with a vehicle engine, the lead jacket with the drag caused by serpentine driven accessories, the ripping the sleeve off with a UDP, and the cart of bricks with the drivetrain of a car and the dyno rollers and you should see the picture more clearly. This is why a UDP technically does not "add" hp per se but it does free up hp that would have been otherwise used to turn serpentine accessories rather than turn the rest of the drivetrain of the vehicle. The less percentage of the total engine power used to turn serpentine accessories means the more of it remains to make it to the rear tires to accelerate the vehicle.