The old HP vs TQ debate.

iadr wrote:

ProDarwin wrote: I was about to create an excel/graph to educate those in the wrong... but jsquared already posted one and is 100% correct. I'm ashamed that this is still a debate that pops up on this forum :(

F=MA, or A=F/M Force is measured in, among other things, Lb-ft. Power doesn't enter into it. It's a derivation for other uses. So in addition to your insulting implications, you are wrong.

Solve that for a vehicle. Remember, Force = power / velocity.

accel = power/(mass*velocity)

Streetwiseguy wrote: My IT Neon has a 7400 rpm chip. The torque starts to drop off fairly dramatically above 7000, but if I shift at 7000, people pass me, because 7400 in third is putting more torque to the axles than 5500 in 4th.

This is one of the reasons I'm having trouble with the concept. It makes sense to me with little 4-bangers where the torque peak is so high in the RPMs. But with a big honkin V8 with the torque peaking relatively lower, its hard for me to wrap my mind around how getting the most torque could happen 3000 rpms above the torque peak.

... but its slowly sinking in that its because the multiplier in the lower gear is making more torque even though the curve is on the downslope. I just graphed it out and its making more sense to me. I'm a very visual person.

iadr wrote: It's much more correct to say hp is a measure of rate of torque, actually, but whatever.

Its fine to look at HP as a rate of TQ. You can use TQ for all acceleration equations, as long as you include angular velocity, which converts it into... power.

You won't find a valid equation for acceleration that doesn't involve either A) power, or B) Torque and RPM.

Anyone have any links to free graphing tools for this purpose?

MrJoshua wrote: Anyone have any links to free graphing tools for this purpose?

https://www.openoffice.org/product/calc.html

I'll dig up a spreadsheet and come back. I made one specifically for swank in an earlier thread for a similar purpose.

Wham. Hit me like a ton of bricks.

I had all the right info, just didn't put it together right. I berkeleyING GET IT NOW.

Why only 3 gears?

Also what shift points?

nocones wrote: Why only 3 gears? Also what shift points?

None of the shift points.....E36 M3 be cvt.

https://www.dropbox.com/s/jpb6p71led7ick0/Accel.xls?dl=0

Download & edit the green cells to your liking. Don't put too much faith in the "launch" stuff. Its good for approximating some cars though.

Sheet is currently setup for a 770kg exocet and miata gear ratios... which explains the crazy 1/4 mile times with a 500whp engine pretty much no matter when you shift. Obviously you should change all that to reflect whatever vehicle this is going in and the results will be a lot less silly.

Note there is a "shift point" setting in there. Feel free to move it down and watch your 1/4 mile time change accordingly (again, don't put too much faith in the #s due to the launch). Also, note there is no shifting delay.

Streetwiseguy wrote: My IT Neon has a 7400 rpm chip. The torque starts to drop off fairly dramatically above 7000, but if I shift at 7000, people pass me, because 7400 in third is putting more torque to the axles than 5500 in 4th. Also, I came here to say that horsepower is how fast you hit the wall, torque is how far you move it.

This is exactly what we have noticed with the SHO's. Damn things dyno chart looks like a bag of cats on PCP. 2 separate torque peaks and curves before/after 4k, and a rather alarming jump in HP @4k. Only thing I've personally seen crazier was the Muzzys bike. That thing was all over the place.

not gonna be like the turbo theory thread, not gonna be like the turbo theory thread.

I just look at the equation, there have been more than a few great examples on here.

Wiki has some great information on this one.

nocones wrote: Why only 3 gears? Also what shift points?

Because I'm lazy

and I just used 7000... again, because I'm lazy.

In reply to curtis73:

I like your style

ProDarwin wrote: https://www.dropbox.com/s/jpb6p71led7ick0/Accel.xls?dl=0 Download & edit the green cells to your liking. Don't put too much faith in the "launch" stuff. Its good for approximating some cars though. Sheet is currently setup for a 770kg exocet and *miata gear ratios*... which explains the crazy 1/4 mile times with a 500whp engine pretty much no matter when you shift. Obviously you should change all that to reflect whatever vehicle this is going in and the results will be a lot less silly. Note there is a "shift point" setting in there. Feel free to move it down and watch your 1/4 mile time change accordingly (again, don't put too much faith in the #s due to the launch). Also, note there is no shifting delay.

I put in most of my parameters. I think the 11.3 ET is a bit optimistic But playing with shift RPM between 6200 and 7000, 6600 yielded the fastest trap speed at 128.2

But that is a very interesting and useful spreadsheet.

https://www.dropbox.com/s/e5kb5ahyxjwszwu/Accel-1.xls?dl=0

And if you're curious (although I wouldn't be using it in the 1/4 mile) add a spot for 6th gear.

Yeah... 1/4 mile just makes the comparison nice and easy though.

You still have the exocet drag area and drag coefficient in there. Changing those to whatever you are building may help. Also, to get a more accurate launch, try setting the launch accel value to your max accel in 1st gear (8.1m/s^2 in this case), and set launch rpm to the RPM where this occurs (roughly 4k in this case).

I should probably make it do this automatically.

I'll add a 6th gear too

Anyway, if you look at the chart in there... see how shifting at 6600 creates a dip in the chart between gears? That means some Power (acceleration) is left on the table. The spreadsheet doesn't account for different shift points for each shift, but this shows that your mythical vehicle would benefit from such a thing. 6000 lines up well for the lower gears, but as you go into higher gears that shift point will move up each time.

Edit: Range looks like 6000 for the 1-2, and 6750 for the 4-5

I had a thread on this very subject recently. I`ll find it in the morning. I learned a lot.

https://grassrootsmotorsports.com/forum/grm/stupid-and-unrealistic-which-is-faster-question/75502/page1/

Maximize hp under the curve. Don't have time to read and digest and such. Get a desktop dragstrip sim and try them both. You'll see it there.

iadr wrote:

Duke wrote: Mosey over to neons.org and look in the FAQ. There is an excellent essay on shift points by Chrysler engineer and road racer Erich Heuschele.

Based on not being able to find what you refer to, I think you may be thinking of this: http://faq.neons.org/faq/FAQ_RACE.html#powerNshifts ? by Ed Lansinger which I find a little confusing past the half way point. He does say this, which may help you get yourself clear on this:

ed said: But, you ask, isn't your acceleration greatest at the torque peak? Yes, it is! BUT ONLY WITHIN THAT GEAR. The next gear down will give you even greater acceleration at the same speed, unless the vehicle speed is too high for that gear.

Yeah, sorry. That's exactly what I was referring to. Ed is a GM engineer. It's been a while since I was involved with that FAQ. Thanks for getting the correct link.

Duke wrote:

iadr wrote:

Duke wrote: Mosey over to neons.org and look in the FAQ. There is an excellent essay on shift points by Chrysler engineer and road racer Erich Heuschele.

Based on not being able to find what you refer to, I think you may be thinking of this: http://faq.neons.org/faq/FAQ_RACE.html#powerNshifts ? by Ed Lansinger which I find a little confusing past the half way point. He does say this, which may help you get yourself clear on this:

ed said: But, you ask, isn't your acceleration greatest at the torque peak? Yes, it is! BUT ONLY WITHIN THAT GEAR. The next gear down will give you even greater acceleration at the same speed, unless the vehicle speed is too high for that gear.

Yeah, sorry. That's exactly what I was referring to. Ed is a GM engineer. It's been a while since I was involved with that FAQ. Thanks for getting the correct link.

From that same link:

A car accelerates hardest with gearing selected to stay as close as possible to the engine power peak, subject to the traction capability of the tires. Not all cars should be shifted at the redline for maximum performance.

iadr wrote:

ProDarwin wrote: I was about to create an excel/graph to educate those in the wrong... but jsquared already posted one and is 100% correct. I'm ashamed that this is still a debate that pops up on this forum :(

F=MA, or A=F/M Force is measured in, among other things, Lb-ft. Power doesn't enter into it. It's a derivation for other uses. So in addition to your insulting implications, you are wrong.

iadr wrote: Acceleration force can be calculated as F = m a where F = acceleration force (N) m = mass of car (kg) Acceleration work can be calculated as W = F l where W = work done (Nm, J) l = distance moved (m) Acceleration power can be calculated as P = W / dt where P = power (J/s, W) Also, I think this is where Prodarwin is getting mix up, tq=radius x force. but if for no other reason than that the radius doesn't change anywhere with a given drivetrain ("system") during the acceleration, we do not use it.

Great equations. You are missing the point. All that works fine and dandy to find accelerative force at a particular moment in time. To find peak acceleration over a distance, say, a quarter of a mile, you have to factor in distance and time. Force applied over a certain amount of distance with respect to time sounds an awful lot like... POWER. From the link you posted:

http://faq.neons.org/faq/FAQ_RACE.html#powerNshifts said: OK, so what about power? As has been noted by a previous contributor, Power (hp) = Torque (ft-lb) * RPM / 5252. Note that power is also force * velocity, specifically: Power (hp) = Force (lb) * Velocity (MPH) / 374 That's net horsepower, which is engine power minus losses like transmission and tire friction. The force is the sum of the longitudinal forces at the contact patches of the two driven tires. Hmmm... P = F * V ...rearrange to get F = P / V ... that means that you get the maximum force pushing the car if you maximize your *Power* at any given velocity. This gives us another useful rule: Shift to maximize engine POWER, not engine torque!

and:

http://faq.neons.org/faq/FAQ_RACE.html#powerNshifts said: There are no exceptions; a car running at its (net) power peak can accelerate no harder at that same vehicle speed. There is no better gear to choose, even if another gear would place the engine closer to its torque peak. You'll find that a car running at peak power at a given vehicle speed is delivering the maximum possible torque to the tires (although the engine may not be spinning at its torque peak). This derives immediately from first principles in physics.

Practical example: You have two cars with 300 ft-lbs of torque and the same gearing, but with different power output since they make torque in different parts of the power band. One completes a quarter of a mile in 14 seconds. One completes a quarter of a mile in 12 seconds. They both performed the same amount of work (same distance and same torque applied), but one of them did it in less time. Same work done in less time means more power was used. Car that covered the distance in less time did so due to POWER, not torque.

iadr wrote:

ProDarwin wrote: I was about to create an excel/graph to educate those in the wrong... but jsquared already posted one and is 100% correct. I'm ashamed that this is still a debate that pops up on this forum :(

F=MA, or A=F/M Force is measured in, among other things, Lb-ft. Power doesn't enter into it. It's a derivation for other uses. So in addition to your insulting implications, you are wrong.

F=MA Force is equal to mass times acceleration. acceleration will have a time squared unit. I am not sure how to express force in Lb-ft.

Still reading though. Only on page 2.

okay, I looked it all up...

F = lbs. (that's it)

M= slugs = ((lb (force)*(Seconds^2))/ft)

A = ft/(second^2)

it is not possible to make Force = lb-ft.

Area under the curve is where it's at.

jsquared wrote: TQ man is wrong. ... To find shift points, you need power to the ground in each gear. In absence of measuring directly, you can approximate. Multiply the power curve by each gear ratio...

Please show me a gear train that multiplies or divides power output.