Please explain physics to me

[2015ghost]

So if I have a car and for arguments sake it makes 400 hp. People say figure 20% for drivetrain loss. Ok so 80hp. But if my car makes 800hp and you still say 20% drivetrain loss then the drivetrain now takes 160hp to turn! How does this translate? What in the flux compasitor is this witchcraft?

[pyroguy]

Subscribed for an answer.

[rebelyell22]

e=mc^2

[chowser51]

Ask someone with 800hp to go dyno their car and report back.

[0-120]

It's also worth noting that the more powerful you make your engine, the greater the thrust force and angular acceleration it's able to exert on the drivetrain, generating even more friction and heat in the process. But because both steady-state and dynamic friction vary depending on engine speed, engine load and the efficiency of the engine and drivetrain's design (how well they limit friction and the associated thermal conversion of torque to heat), there's no way to apply a universal percent loss to it. Nor is it possible to apply a fixed drivetrain loss figure to your car (say 60 whp from my RevUp G35 example), because as you modify the engine and increase its output its ability to generate thrust force and angular acceleration also increases (though not in a linear fashion).
In the end, there's no easy way to estimate the drivetrain loss your vehicle experiences on the road or even on the dyno. Coast-down tests are sometimes used on a dyno to attempt to measure frictional losses, but because this test is not dynamic (meaning they're not done while accelerating, but rather while coasting to a stop with the direct drive gear engaged but the clutch depressed so that the engine and transmission aren't linked) it really only captures steady-state drivetrain losses as well as rolling resistance. So rather than attempting to convert your vehicle's dyno-measured wheel horsepower to a SAE net horsepower figure using a percentage or a fixed horsepower value, you're far better off accepting the fact that these two types of horsepower measurements aren't easily correlated and forego any attempt at doing so.

Tldr it isnt a fixed percentage.

Source: http://www.superstreetonline.com/how...in-power-loss/

[Royal Tiger]

A stock L99 SS is about 22% loss at the rear wheel and the percentage lessens as peak HP increases. It’s also highly dependent on the transmission (obviously) so you can’t easily cross vehicles and just say 20%. It’s not a bad baseline though to be somewhat close.

[silversleeper]

Because the losses are mostly friction. This energy would be wasted mostly as heat, with some entropy changes (stuff grinding down). Same for brake pads but there is much more heat and entropy change (brake dust). Sometimes you push your brakes and scrub off 30hp and sometimes hundreds of hp. Some energy is wasted as light (glowing orange) or noise but that isn't a significant amount vs the heat in what you're asking.
Friction can actually go down as the speed increases but applying more force, as you do with your brake pads causes more friction...unless you're an ice skater and the blades melt the ice due to the pressure and friction and the water on ice reduces the friction.
Doing unseen things like swirling around oils and fluids (including air) in the engine, trans, rear, and bearings are other examples of wasted energy aka friction.

[CamaroFred]

It has always been true that the more power you use, the more loss you see.
Lean on a drill and it's harder to turn.

[mikeinmobile]

Was told by knowledgeable builders when I was building the 455 for my Cutlass that the 400 THM tranny robs 75hp. I didn't think to ask what a 350thm scrubs. I knew not to even try a 350 as my buddy w/a 396 Impala had already fried 2 350's without much effort.

[pyroguy]

Originally Posted by rebelyell22

e=mc^2

And Force = mass x acceleration but that doesn’t help here.

Originally Posted by 0-120

Tldr it isnt a fixed percentage.

Source: http://www.superstreetonline.com/how...in-power-loss/

Interesting read, but unless I missed it did it spell out that the drivetrain loss is a linear percentage as horsepower increases?

[christianchevell]

Just so you know there are actually lock up converters and so much more like torque convertors with different rates of loss that calculating things out is a lot more complicated on a car by car basis with the varied parts.

A convertor btw slops around throwing the fluid with its little fins making pressure so imagine that...and imagine the torque getting to the wheels having to come from those little valves all over in the transmission flowing that fluid then transferring power through a couple u -joints to split off a gear to another gear that's attached to a pair of axles...…. And what kind of rear..... cause that matters.... a locker...a one legged dog.....etc now really blow your mind and figure the HP is measured off the torque...because torque is what moves you HP just says hey the engines this efficient making that torque...……


And you could have that 800 hp car with say 650 torque get its ass kicked by a car with 650 hp and 650 ft lbs of torque being lighter...kind of like lining up a ZL1 against a Hellcat.....or Demon..... wow how mind friggin boggling...LOL And yes of course if your even on a dyno measuring the loss and if its load bearing or full of SSSSSS...……...

[silversleeper]

Originally Posted by mikeinmobile

Was told by knowledgeable builders when I was building the 455 for my Cutlass that the 400 THM tranny robs 75hp. I didn't think to ask what a 350thm scrubs. I knew not to even try a 350 as my buddy w/a 396 Impala had already fried 2 350's without much effort.

The turbohydromatic 350s did lose less power. But they would break with less hp.
Interestingly the 2 speed powerglide transmissions of the 60s lost less hp. If you couldn't use the extra torque of more gears due to tire spin limitations, they were a better choice when built up for drag racing.

[Moto-Mojo]

The good news is, a study in 2010 (coincidence with introduction of the 5th gen?) suggests that the laws of physics as we know them, may not be the same in all parts of the universe. I’m thinking the HP gains in another sector could be huge! Or really parasitic.

[Jeff_SS]

Originally Posted by chowser51

Ask someone with 800hp to go dyno their car and report back.

734rwhp reporting back