The percentage is because you are acceleration a load. Think it through. It takes more power (a greater number because the percentage stays the same) so it’s not a fixed number but a fixed percentage. (a powerglide is about 19-19.5% and a TF is about 21%). That means that it robs the same PERCENTAGE of power no matter what. 21% of 500 hp is 105 hp and 21% of 1000 hp is 210 hp.

So the percentage stays the same but the actual power consumption number goes up because you are dealing with a percentage of how much hp it takes to drive a gear box.

Look at NHRA Pro Stock and Mountain Motor Pro Stock. One is 500 CID and about 1500ish hp. The other can be some really big CID, BUT the power doesn’t go up as a percentage of CID because friction losses are also a percentage.

So let’s say you are looking at a 500 CID engine and comparing it to a 700 CID engine. At 1500 hp, you get 3 HP/CID. And the 700 CID engine makes 1750 hp which is 2.5 HP/CID. Because the friction losses are a percentage of total hp, the bigger engine makes more hp but is less efficient (2.5 HP/CID rather than 3.0 HP/CID).

If you made the bigger engine even bigger, the flywheel hp would (should) go up but the HP/CID would go down.