BRZ / FR-S Boxer Engine Dyno Powerband revealed

[bambbrose]

Originally Posted by Deslock

1. What you feel comes from force at the wheels, which comes from wheel torque.
2. Wheel torque != engine torque, though they are proportional for any given gear ratio.
3. For any given velocity, wheel torque increases if power increases (regardless of engine torque).
4. The typical dyno plot does not show wheel torque (discussed last November in the FR-S/BRZ vs. Genesis Coupe thread).

If you are going to correct us on on a nuance, at least get it right. What you feel technically comes from the seat pushing you forward. Draw a free body diagram of your body when accelerating



If a balloon is floating in a car, and the car accelerates, does the balloon go backwards from the acceleration?? This was a junior level physics problem for my mechanics class

[Guff]

Originally Posted by bambbrose

If you are going to correct us on on a nuance, at least get it right. What you feel technically comes from the seat pushing you forward. Draw a free body diagram of your body when accelerating



If a balloon is floating in a car, and the car accelerates, does the balloon go backwards from the acceleration?? This was a junior level physics problem for my mechanics class

Lol Professor Bambbrose. Thank you for this.

[Deslock]

Originally Posted by ahausheer

So basically Hp is an enabler of torque? Torque moves you forward and hp determines how long that torque can be applied. Off topic I know. Ill discuss elsewhere.

It's more on-topic here than the usual threads that power vs torque comes up in. Power -more or less- tells you how quickly you can apply a torque.

Think of a bicycle. You apply a force to the pedal, which turns the crank. That force is applied to the chain, but can also be measured in terms of torque (rotating force) around the bottom bracket.

You can push a pedal hard when it's stopped or rotating slowly. The limit of how hard you can push on the pedal is akin to an engine's torque rating.

How fast you rotate the pedal is akin to an engine's speed.

If you downshift, it takes less force to push the pedal, but now you can pedal faster. The combination of how much force you apply and how quickly you pedal is akin to an engine's power.

If you downshift so that you're pushing half as hard but rotating twice as quickly, you'll deliver the same amount of power and accelerate the same. But if you downshift and can deliver the same force to the pedal twice as quickly, you'll have twice the wheel torque. Even if you push with 25% less force, but pedal twice as fast, you'll accelerate more than before the downshift.

Just like in a car: if you downshift so that you make more power, you make more wheel torque and accelerate more (even if you make less engine torque after the downshift).

It's not a perfect metaphor, but the principle is the same.

Originally Posted by bambbrose

If you are going to correct us on on a nuance, at least get it right. What you feel technically comes from the seat pushing you forward. Draw a free body diagram of your body when accelerating

I'll see your FBD comment and raise.

What I posted is correct: what you feel *comes from* the force at the wheels (there's a reason I didn't write that what you feel *is* the force of the wheels). I originally drafted "What you feel is the seat pushing you, which comes from force at the wheels, which comes from wheel torque." but I decided it was unnecessarily wordy and too douchy to put it that way, so I trimmed it.

Besides, my post wasn't nuanced. This is nuanced: what you feel (unless you drive around topless) is your shirt pushing on you, which comes from the forces transfered from the tires to the wheels through the car to your seat to your clothes to you.

Originally Posted by bambbrose

If a balloon is floating in a car, and the car accelerates, does the balloon go backwards from the acceleration?? This was a junior level physics problem for my mechanics class

So that's not covered until junior year now? Back in my day, we did that one as a freshman.

I'll let someone else answer. Since we're off-topic anyway, here's some extra credit: Explain the differences, if any, for how it works for balloons filled with helium vs air.

[serialk11r]

Originally Posted by Deslock

So that's not covered until junior year now? Back in my day, we did that one as a freshman.

I'll let someone else answer. Since we're off-topic anyway, here's some extra credit: Explain the differences, if any, for how it works for balloons filled with helium vs air.

Back in oh, 2010, we did that in high school :P
Balloons filled with air have no buoyant force.

[Levi]

Why join the right and left side of the headers together? Could not they be completely seperate?

[SUB-FT86]

Originally Posted by serialk11r

Back in oh, 2010, we did that in high school :P
Balloons filled with air have no buoyant force.

I thought you was much older because you seem so knowledgeable on how the engine works. Age ain't nothing but a number.

[old greg]

Originally Posted by SUB-FT86

I thought you was much older because you seem so knowledgeable on how the engine works. Age ain't nothing but a number.

That's about how old I thought he was, because of how much he thinks he knows.

[7thgear]

Originally Posted by old greg

That's about how old I thought he was, because of how much he thinks he knows.

and you're the smartest one here, right?


as for engine and car dynamics theory, they don't teach that in high-school. Direct application of high-school physics to our questions only comes if you pick up extra material and just read up on it independently.

this is a neat little thing to read for those of you with genuine questions

http://phors.locost7.info/files/Beck..._of_Racing.pdf

also, with regards to tuning, here is a good book that talks about fuel injection, it's outdated (most of the cars that use the systems described are disappearing from our roads) But still good theory.

http://www.amazon.ca/Bosch-Fuel-Inje.../dp/0837603005

[bambbrose]

Originally Posted by Deslock

So that's not covered until junior year now? Back in my day, we did that one as a freshman.

I'll let someone else answer. Since we're off-topic anyway, here's some extra credit: Explain the differences, if any, for how it works for balloons filled with helium vs air.

I had certainly went over the balloon concept earlier, but to actually solve it independently for homework is another story.

I'm actually quite impressed with the group of guys and our knowledge here at ft86. Great minds think alike?? :happy0180:

[7thgear]

Originally Posted by bambbrose

If a balloon is floating in a car, and the car accelerates, does the balloon go backwards from the acceleration?? This was a junior level physics problem for my mechanics class

gotta specify that it's filled with helium


i had to look it up though

seriously though, how often does one drive with helium balloons floating in the car, haha

[bambbrose]

Originally Posted by 7thgear

gotta specify that it's filled with helium


i had to look it up though

seriously though, how often does one drive with helium balloons floating in the car, haha

How else would it be floating

[Gardus@Supersprint]

If you're travelling in a train that goes at the speed of light, and then you start walking toward the head of the train, are you going faster than light?

[7thgear]

it's all relative

[val_lixembeau]

Originally Posted by ahausheer

So basically Hp is an enabler of torque? Torque moves you forward and hp determines how long that torque can be applied. Off topic I know. Ill discuss elsewhere.

Exactly the opposite. HP is a measure of how "quickly" the torque can be applied.

Think of it this way, torque is a measure of force, but instead of measuring how hard you can push, it measures how hard you can twist.

In a straight line, you've heard that work=force*distance right? What power measures is how fast you can do that work.

Now let's translate that to circular motion...

Work is now torque applied over a certain number of revolutions. So power is torque times revolutions over time. That's why we sometimes say that power is just a number derived from torque.

Imagine two engines with the same peak power, but one with low torque and one with high torque. We'll use perfectly flat torque curves for simplicity. That would mean that the low torque engine needs to rev at higher rpm to produce the same power as the high torque engine.

In theory, these engines placed into the same car could produce identical acceleration if they were geared appropriately. The low torque engine would just need to rev higher. The problem is, people don't like to rev their engines, and manufacturers don't like to gear that way because of cost, mileage and reliability.

And that's why most people think of torque numbers as being responsible for the acceleration that you feel. Because low torque engines aren't geared low enough to produce the same acceleration as high torque engines, and even if they were they might not be able to rev high enough to take advantage of that gearing.