Horsepower % lost

[Lucky]

Originally Posted by bmussatti

Lucky, I follow your example, and would agree, but in Tholyoak's example the car is the same (without a beefed-up tranny). So he does pose an interesting question to ponder.

Guess I should read better...

Even so, I believe this is easily explained by the following High School Physics formula for the friction force observed between sliding surfaces:

F = mu * Fn

Where:
F = the force due to friction (loss in a tranny, for example)
mu = the coefficient of friction between two moving surfaces
Fn (as in "normal force") = the force applied perpendicular to the two moving surfaces

The key parameter above is "Fn", which inside a tranny occurs where gear surfaces touch and shafts push sideways against bearings (to counteract the torque that is spinning the shaft). As this "normal" force goes up, friction loss (F) goes up in a linear manner. So yes, the climbing loss as more power is put through a tranny makes perfect sense.

Yes, rotational inertia remains the same, but as friction loss climbs the inertia becomes less of a factor.

[blue2000s]

Originally Posted by Lucky

Guess I should read better...

Even so, I believe this is easily explained by the following High School Physics formula for the friction force observed between sliding surfaces:

F = mu * Fn

Where:
F = the force due to friction (loss in a tranny, for example)
mu = the coefficient of friction between two moving surfaces
Fn (as in "normal force") = the force applied perpendicular to the two moving surfaces

The key parameter above is "Fn", which inside a tranny occurs where gear surfaces touch and shafts push sideways against bearings (to counteract the torque that is spinning the shaft). As this "normal" force goes up, friction loss (F) goes up in a linear manner. So yes, the climbing loss as more power is put through a tranny makes perfect sense.

Yes, rotational inertia remains the same, but as friction loss climbs the inertia becomes less of a factor.

Yup, the amount of friction is directly proportional to the amount of force. Rotational inertia is a very minor contributor to drivetrain losses.

If that small engine in the example is at full throttle making all of it's 100hp and the bigger engine is at part throttle, making the same 100hp, the losses in the system will be the same, but add more throttle to the big engine and friction goes up in the pistons, crank, gears, axle joints and tires.

[tholyoak]

Yes the frictional loss will increase, but do you really think it would account for a 30 hp loss in the two examples, I for one don't think so, as the amount of heat generated would be pretty extreme and lead to failure of parts in pretty short order.

Anyway, I think trying to extract flywheel numbers from rwhp numbers is pointless.

Todd

[blue2000s]

Originally Posted by tholyoak

Yes the frictional loss will increase, but do you really think it would account for a 30 hp loss in the two examples, I for one don't think so, as the amount of heat generated would be pretty extreme and lead to failure of parts in pretty short order.

Anyway, I think trying to extract flywheel numbers from rwhp numbers is pointless.

Todd

Yes, it will increase in direct proportion of the power (actually torque, but whatever) increase.

[Lucky]

Originally Posted by tholyoak

...the amount of heat generated would be pretty extreme and lead to failure of parts in pretty short order...

Believe it. That is exactly why there are trannies desiged for 300 HP and different ones for 100 HP.

[blue2000s]

Every system in the transmission is built with what's called a factor of safety, which means they are overdesigned for purposes of functionality under extreme conditions, accounting for any manufacturing variations/defects, accounting for any misjudgement in engineering or inaccuracy in calculation, and longevity. When a more powerful engine is placed in a car that wasn't designed to accept it, this margin for safety is reduced, but it still may be enough for the car to work, at least for a while.

[Grizzly]

Originally Posted by blue2000s

Every system in the transmission is built with what's called a factor of safety, which means they are overdesigned for purposes of functionality under extreme conditions, accounting for any manufacturing variations/defects, accounting for any misjudgement in engineering or inaccuracy in calculation, and longevity. When a more powerful engine is placed in a car that wasn't designed to accept it, this margin for safety is reduced, but it still may be enough for the car to work, at least for a while.

So that's why I go through so many AODs.

This is what I think Tholyoak is saying:

Let's say you have a 986 Boxster with 240 HP. If it looses 15% HP (or 36 hp) you have about 204 HP at the wheels.

Now you do a engine swap with a 3.6L engine that has maybe 330 HP. It will be in the same car with the same exact tranny, tires, everything. So, how much HP to the wheels? 330- 36= 294 HP or 330-15% (50 hp) = 280??

[JackG]

Originally Posted by Grizzly

So that's why I go through so many AODs.

No, it's your right foot that's to blame.