j9fd3s

doesnt seem to be online, but in the paper catalog racing beat has the power numbers it takes to keep an rx8 rolling at various speeds in 6th gear.



it was something like 64hp to go 60mph

48hp to go 45 mph



something like that.



is that loss number a constant? or does it change with load?



if we dynoed the car steady state, it takes 64hp, if we floored it and went thru 60mph, does it still take 64hp?

Kyrasis6

It is simple physics, in order to accelerate a car you have to be applying more energy than what it takes to maintain the current speed. The faster you accelerate the more power you will need.



For instance you take a valvetrain from a piston engine and run it on a spintron at 4,500 rpm (camshaft speed) and it may take 14 hp to turn. Now if you start the same test at say 1,500 rpm it may only take 3 hp to run but if you accelerate it at a rate of lets say 500 rpm/sec (again camshaft speed) it may take over 50+ hp to accelerate the valvetrain at that speed.

heretic

That's inertial loading.



The main problem is that gears are, to an extent, lossy, which is where "percentage" losses come from.



Think about how hot the diff and transmission fluids get after 20 minutes of hot lapping, versus 20 minutes of circling the neighborhood. That heat came from the engine, and was generated via absorbed power.



Tires are lossy as well, and the losses are non-linear. Gears may be too, but the tires I know from a paper I rear years back where Audi claimed that AWD was actually more efficient at higher power loadings because of this nonlinearity. Now, the only problem is, after calculating in the gear losses, and seal friction, the crossover point where AWD became more efficient than 2WD was roughly 100mph. Maybe not so much a problem in the motherland...



Normal losses, I believe, are on the order of 30-40hp at 60mph, give or take a few. It's been a while since cruise power figures have been commonly released.



quick edit: Something that may make immediate sense because most people have experienced it: Chain drive has been with us for a long time for bicycles because it is probably the most efficient way of transferring power. It is about 98 to 99 percent efficient. Geardrives are typically around the 85% efficiency range, which if you've ever rode an English 3-speed, you'd know right off. They feel like you're pedaling through molasses.



Now, to figure out how to get a bunch of Number 40 chains in a transmission case, or a derailleur system that can handle 200 horsepower!