Noize

iTrader: (24)

5th gear sucks. Hold 4th to an inch from boil for the best acceleration.

x838nwy

TrinaBabe, I think you've actually confused the issue regarding power and gearing.

As djh said, you never make more power than the flywheel dyno incates. Basically,

force = mass x accelration, and work done by a force = force x distance (a pretty loose definition, but serves the purpose here) and since power is the rate at which the work is done then power = mass x accel x speed.

If you take the engine power, subtract your tranny loss and divide by the wheel rotational speed (= some constant x vehicle speed), you get the torque going through the wheels (multiplied by some comstant).

Under the same parameters (throttle, rpm, etc) the engine will make the same power. The gearing affects the wheel rotational speed (at the same rpm) and so affects the accelration.

Now if you work through this, you'll find that it's a heck of a lot simpler just to start with the torque curve and get the acceleration at each rpm for each gear and go from there (which is what TedB does I think, I don't have excel here).

I have not included tranny losses, but you can subtract that from the flywheel hp in as sophisticated a manner as you like but the principle still holds.

The moral of the story, however, is that just because a car has higher max.hp does not necessarily mean it will be faster. Also sometimes, it is more beneficial to have a wider usable rev range and fewer gears than to have a very peaky engine and lots of gears.

TrinaBabe

iTrader: (3)

Yes.. this guy that made the template sheet you uploaded did the EXACT same thing as I did just entered in the correct math to make it "real" numbers instead of mine which is using arbitrary "power" values.

None the less.... read in the second tab of his sheet.... it reads "Torque Multiplier" for each gear.

In physics your motor does make the same power... but the power to the ground does change. It is a pully system in essence. An electric motor making 1 FtLb of TQ couldn't lift 10 lbs in a 1:1 ratio could it? No. But now hook up a pulley system (Gear box) and make it a 1:30 ratio. You have now made it so it could lift 30 Lbs in a said amount of time over a said amount of distance.

And yes, I like how his chart enters in G's vs Speed. It is a very easy way to make it readable... My chart just has the "G"s per RPM per Gear.... it doesnt tell you what speed your going hence the reason you need to figure out the RPM drop on your own. He entered all that in for you so it saves some time but the charts do the exact same thing.

TrinaBabe

iTrader: (3)

And let me re-explain again:

Yes, the MOTOR does not make a different amount of power at an RPM. However, the tires DO see a different amount of power per gear. You multiply the engine power by the drivetrain... that is why we can spin our tires in 1st but not 4th.

Like you said, power = mass x accel x speed... so we can obviously figure out the mass will stay constant. Now assume we are going 10 MPH to start with. Floor it in 3rd from 10 MPH -> 30 MPH and it takes 3 seconds... the "power" would be the 20MPH/ 3 seconds.... Now floor it in 1st and it takes you less time obviously so say 1 second... 20MPH/1 second. You are making more power in 1st at the wheels. It is VERY simple physics.

More simply put: You can accelerate FASTER in 1st gear than 3rd.... If the power was the same to the ground how is this possible considering mass (Stays the same) and speed (Which we keep the same)... the only other variable is accel (Which first accelerates faster) Unless Newton was wrong this whole time and his formula sucks

Ted B

iTrader: (6)

From 2000-8000rpm:

In 1st gear - accelerates from 11-45mph - a net change of 34mph and relatively little air resistance.

In 3rd gear - accelerates from 24-95mph - a net change of 71mph and considerably greater air resistance to be overcome.

Naturally, the 3rd gear run happens more slowly because the same amount of force must do a much greater amount of work. Gearing simply determines how much power is condensed into a given net change. Higher numerical gearing simply allows a given amount of force to perform a smaller amount of work.

It's no more complicated than that.

TrinaBabe

iTrader: (3)

And I agree The problem is most people dont understand that. That is why you can figure the power from any gear... The part people dont get is the simple acceleration part. Since you are geared lower, you will accelerate from say the 24 MPH -> 45 MPH faster in 1st than you would third. Same MPH difference, just different acceleration rates. Take yours for example and we will dummy it down for everyone else:

11-45mph - a net change of 34mph takes 2 seconds
24-95mph - a net change of 71mph takes 7 seconds

Assume for this stupid thing we accelerate with a flat TQ curve (Which isnt true but thats why we made this whole discussion to figure out shift points).

24-45 in 1st takes 1.24 seconds
24-45 in 3rd takes 2.07 seconds

Air resistance and everything else is obviously the same because it is the same speed.

The fact of the matter is your acceleration rate changes with the gearing. Instead of 1FPS/Sec it may turn into 6 FPS/Sec even if you are making the same power at the engine.

djh

Um, here you're just plain wrong. The reason you can break the tires loose in 1st is because the force exerted is much greater, however at the instant they break loose they're not going very fast! Once spinning the force exerted against the ground is very low. If gearing increases the torque it has to decrease the revs. Just like with your compound pulleys, you increase the force but decrease the speed, no exceptions.

Dave

Ludikraut

iTrader: (17)

Interesting post. I have posted some similar things in the past, including:

torque vs. speed (comparing a Vishnu stage 1+ to an AMS 3071):



similar chart to Trinababe's, but for a stock Evo 8:



l8r)

TrinaBabe

iTrader: (3)

Oh and I plotted an almost stock car to figure out the shift points... They are all still above 7k which means our gear ratios are pretty well designed for a stockish car. So for all you people wondering what a good shift point is for your car... assuming you dont drop power REALLY badly you are always going to be best off by holding it to around 7.2k for a stock car. In this guys case (Evo IX with MBC and exhaust) he is best off shifting at these points:

1-2 @ 7650
2-3 @ 7150
3-4 @ 7100

And that is on a car that is dropping power FAST. (The TQ is the line to look at) Look at how badly it drops off:

TrinaBabe

iTrader: (3)

I think we all knew spinning tires means power aint making it to the ground Thanks for that lesson though.

And yes, EXACTLY my point.... you are decreasing the speed but increasing the force pushing the car. The IDEA here is to figure out when does the extra force accelerate the car slower than the increased MPH gain? I didnt think it was this hard to figure out. You are accelerating LESS MPH per RPM in a lower gear... TRUE. You are however accelerating the less mph/rev much much faster than you would be in the higher gear. So yes, in 1,000 rpm difference of 1st to second you travel more distance in second obviously. The problem is you do it much more slowly.

I have every single math equation to figure it out, I have done it, I have proved it, Ted B found another document which does the same thing and produced the SAME numbers. It is VERY simple physics. It isnt how many MPH per Rev it is MPH per Rev per TIME... time being the key.

Go read some simple physics and figure it out my friend. Ive done all I could. Just to be nice here ya go AGAIN:

Lower gear ratio multiplies the force trying to spin the tires forward.

Since our cars drop off TQ in the higher RPM range sooner or later the TQ gets low enough that even after you multiply it, the next gear has more.

We are talking about force spinning the tire. Nothing else.

djh

Don't be an ***. You started out trying to dispell confusion but made the same mistake a lot of people do -- confusing torque, power, etc. You said power can be multiplied through a set of gears. It can't. I know you really know that, but if you're trying to explain something, get the damn explanation correct. It doesn't matter how many math equations you have if you don't apply them correctly. When you do, you'll realize the simple prescription of plotting wheel power vs. road speed is exactly what Ted's spreadsheet does.

Dave

TrinaBabe

iTrader: (3)

Yes I understand fully the fundementals of how it all works. I was trying to make it the most simple way for people to understand. Obviously the power is the same regardless but the acceleration rate changes dramatically. The worksheet Ted found does the exact same thing that mine does. His just also displays road speed for each gear. The only thing road speed does is help you figure out when the acceleration of the lower gear starts to be worse than the next gear. Mine you need to draw a line.... it was easy enough for me and saved me probably an hour of entering formulas to get it to display roadspeed. I am very glad Ted found this spreadsheet because it looks much nicer than my crude version and I would be too lazy to ever make a good looking one but they are the exact same.

TrinaBabe

iTrader: (3)

And yes I applied every calculation (not too many in this case) correctly. They are very simple. Mine measures (A multiple of) Gs vs. RPM vs Gear (JUST as the one Ted found does). He just added in the final drive ratio and tire size to get roadspeed. If you look at the last tab of his spreadsheet it is the same chart that mine was creating.

And I was trying to be nice but when people tell me I am plain wrong when it is more than obvious I am not it gets kinda frustrating.

I have not confused TQ to power etc etc.... TQ is a form of power, as is HP, Watts, etc, etc... You can measure power with any of the above. Is what is happening is you are confusing power from the motor compared to power at the wheel.

x838nwy

TrinaBabe, I think where you're going wrong is in what you call things.

Torque is NOT a form of power. It's just a force applied with a moment arm. The units of torque is inconsistent with units of power.

The power produced is the torque multiplied by the rotational speed. It doesn't matter where you take this rotational speed. If you take the driveshaft rotational speed, the torque on the drive shaft will be half that at the wheels if the driveshaft spins twice as fast as the wheels. The wheel see exactly the same power at the same engine speed which is geared to the wheel. The reason it is easier to loose traction in lower gears is because the wheel rotational speed is lower and therefore the torque is higher. But again, the same power.

If we ignore transmission losses, the power from the motor is exactly the same as that at the wheels. Even if you include the effects of tranny losses, you will only get less power at the wheels. Gears multiply torque, not power. A torque is a torque, when a torque, say, rotates a wheel it does work. The rate at which that work is done is called power.

In your post which quoted me, you managed to get power = 20mph/3seconds, a simple check of units will show that this is entirely wrong since you are saying that power/mass = acceleration, whereas it's actually power/mass = accelration x speed.

As you said it's very simple physics. But it hasn't stopped you getting it wrong, repeating your mistakes and insulting others. I am sure you're aware of the laws of conservation of energy, from which it is simple to conclude that power must be conserved. So you cannot multiply power. You can multiply torque (and lose rotational speed) but not power.

x838nwy

A couple of definitions from answers.com

Power: power, in physics, time rate of doing work or of producing or expending energy. The unit of power based on the English units of measurement is the horsepower, devised for describing mechanical power by James Watt, who estimated that a horse can do 550 ft-lb of work per sec; a foot-pound is the work done when a weight (force) of 1 lb is moved through a distance of 1 ft. The unit of power in the metric system is the watt, named in honor of James Watt and equal to 1 joule per sec; the watt is used for measuring electric power in most countries, even those still using English units for other quantities. In common usage, the terms power and energy have become synonymous; for example, electrical energy is usually referred to as electric power (see power, electric). See also energy, sources of.

Torque: torque, in physics, that which tends to change the rate of rotation of a body; also called the moment of force. The torque produced by rotating parts of an electric motor or internal-combustion engine is often used as a measure of its ability to do useful work [note, NOT the RATE]. The magnitude of the torque acting on a body is equal to the product of the force acting on the body and the distance from its point of application to the axis around which the body is free to rotate. Only the component of the force lying in the plane of rotation and perpendicular to the radius from the axis of rotation to the point of application contributes to the torque. This radius is called the moment arm, or lever arm. The net torque acting on a body is always equal to the product of the body's moment of inertia about its axis of rotation and its observed angular acceleration. If a body undergoes no angular acceleration, there is no net torque acting on it. Units of torque are units of force multiplied by units of distance, e.g., newton-meters, dyne-centimeters, and foot-pounds (or pound-feet).