For those that have difficulty understanding the concept of how a horsepowr measurement can be made where the mass of the rotating assembly does not matter, consider this example:
Imagine a piece of plywood hanging vertically from the ceiling by a rope suspended at two corners.
Now place a force gauge (scale) against one side of the plywood.
Now if someone applies a force to the other side of the plywood, the scale can measure the force.
If I apply a force of 5 Newtons (~ 1 pound force) to one side of the plywood, the scale will measure 1 pound.
Now what happens if I replace the plywood with a steel sheet that weighs 5 times as much as the plywood?
Now if I apply a 1 pound force to one side, what force do I measure?
1 pound!
The mass of the sheet does not make a difference in the measurement of the force at steady state (non-accelerating).
This is exactly how a dyno measures horsepower:
As the dyno drum rotates, the dyno applies a braking force to try to stop the engine from accelerating.
Once it gets the RPMs to stop climbing (steady state, non-accelerating), it measures how much force is applied.
It does this at a set of discrete RPM points through the entire sweep range.
It does notmatter the RATE at which the pull is performed and in fact the slower the pull, the more accurate the data.
I know some that do a single dyno pull in 20 minutes to get the most accurate data with the engine in the most real-world condition.


So I will change my statement about lightweight crank pulleys:
"If you can measure a horsepower difference with a Lightweight crank pulley, you are doing your dyno measurements wrong."

Clearly sarcasm, but that would mean you disagree with my side.
Which part do you disagree with?

I'm just poking fun at the insanity of this thread.

Relax...it wasn't directed at you. Most of this physics stuff goes through my head anyways. I barely passed physics in high school :bellyroll: which is why I'm a CAD technician instead of an engineer lol

Just wanted to share that Honda was using a factory lightweight crank pulley in the Honda Civic Type R car. Was the first car manufacturer using such pulley?

Here is the part no. 13811-PCT-000:

http://honda-tech.com/forums/attachm...-build-005.jpg