Yeah doesnt make much sense to me. How could a drivetrain take 10 HP to turn one time then 50 HP another. As long as nothing but HP was changed with the engine, how could the same exact drivetrain require more power to move?

 

I didn't realize we were talking specifically for automatics.

 

We aren't As a matter of fact we are not talking about Scions specifically. I started this thread as a 'general automotive' question and thats why I put it in off topic and not a specific forum.

I guess I have to go with what Hornet_on_flower said and chalk this one up with the crop circles and alien abductions....LOL. I certainly don't understand it and maybe I need to leave it as one of the many mysteries of the world. Maybe 'Unsolved Mysteries' can do a segment on it? Surely SOMEONE knows, huh?

 

lol..

automatics - usually 10% drivetrain loss on any given number, no matter if its 10hp or 600hp, its usually 10%, in some cases 15% but that just depends on other things envolved.

manuals- Usually can follow 5% drivetrain loss on any given number, but hp can also be gained back with modifications you can't do to an auto..for instance, a high performance clutch *complete kit* could help free up 1-3hp that wasn't there before. Doesn't really effect it much, but every hp counts in some cases.

 

haha thank you

 

OK, let me explain this a little easier so as to understand why it is a set percentage and not a set HP loss. Look at it this way, if you had a 10 CHP car, We are all pretty confident the car will still move. Reason being is you are not loosing a set 10 horse power, you are loosing a percentage of horse power thru the drive train.

Take an automatic for example. As a general rule, when given crank horse power, you can deduct 21% or so. For a manual tranny, deduct 16% or so. It's a loss that is not dependent on horse power, it is in the design of the hydrolics, clutch, gearing, drive train components, etc.

Just like manual transmission cars, cars with automatic transmissions need a way to let the engine turn while the wheels and gears in the transmission come to a stop. Manual transmission cars use a clutch, which completely disconnects the engine from the transmission. Automatic transmission cars use a torque converter.

The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission, the same set of gears produces all of the different gear ratios. The planetary gearset is the device that makes this possible in an automatic transmission.

A torque converter is a type of fluid coupling, which allows the engine to spin somewhat independently of the transmission. If the engine is turning slowly, such as when the car is idling at a stoplight, the amount of torque passed through the torque converter is very small, so keeping the car still requires only a light pressure on the brake pedal.

If you were to step on the gas pedal while the car is stopped, you would have to press harder on the brake to keep the car from moving. This is because when you step on the gas, the engine speeds up and pumps more fluid into the torque converter, causing more torque to be transmitted to the wheels

In addition to the very important job of allowing your car come to a complete stop without stalling the engine, the torque converter actually gives your car more torque when you accelerate out of a stop. Modern torque converters can multiply the torque of the engine by two to three times. This effect only happens when the engine is turning much faster than the transmission.

At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power. This is part of the reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions.

To counter this effect, some cars have a torque converter with a lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency.

 

Good info scion dad. But I dont see how this explains why the more power you have the more you lose. And why its a percentage and not a stagnant number.

I am going to chalk this up to the cop circles and aliens thing and say it is because it is.

But I will propose another question.
Lets use human power:
If I crank a handle that turns gears and turns a wheel, I encounter resistance in the meshing of the gears and the pivot points and what not. Lets say I use a certain amount of power to get it to turn. Now if some one stronger than me turns the same crank, wont it take the same amount of power to get it to turn?
Just because he is stronger than me, doesnt mean that the machine will lose more power through out it.

Or lets use Horses, the root of Horspower:
If one horse can pull a concrete slab across the floor, the resistance of friction is set. It ook 1 HP to move the concrete (yes I know this is not how HP is measured. Its actually how much one horse can move over a certain distance or something, but I am keeping it easy). Now if 2 horses pull that concrete slab, (2HP), it will still take the same amount of force to move that slab.
No more friction is created.





Maybe this is just jibber jabber, but kinda makes sense in my weird thinking.

 

^ you fail to see that by using 2 horses, you are adding weight from the extra harnesses and such. Also by having 2 horses, you have more vet bills and more feed will be used. HAHA...just kidding Nick06.

Anyway, I understand what ScionDad is saying to a point. Yes, the car would move with only having 10 HP, so it is a percentage...BUT I still do not believe it is a SET percentage. I am starting to beieve that it is a gradual percentage. Thank you ScionDad for shedding a little light on the subject.

 

You're correct, it is not a set percentage, but it usually is close enough to get an idea what your loss will be from crank to wheels.

 

But that 10% is only if we are at 100 HP correct? I mean, I fail to see how the drivetrain can miraculously cause the same 10% if 900 more HP were added (a total of 100 HP lost or 10%). So is it safe to say that the more power that is increased, the less percentage of power will be lost through parasiticity? <---Is thateven a word?LOL.