Shift Point Calculations !

[FordFasteRR]

holy crap...

http://www.welltall.com/ymc/discovery/car/shiftpt.html

anybody good with math.. break it down for us ! :)

[CTele02]

well the conclusion says that the red line is the optimal... but obviously most cars aren't engineered that perfectly... i'm taking physics now so im just learning about torque and stuff... so maybe with some free time i can actually understand the equations.

[dragonfighter60]

Man I wish they would put that stuff in english lol.

[seraph0503]

i'm good with math but that's kinda hard to explain unless u can sit down and show someone. plus u have to have an understanding of angular velocity and acceleration because torque is a function of angular acceleration times the angle in radians and angular acceleration is the derivative of the angular velocity. so since force= mass x acell , we get torque= radians x angular acell x sin theta. because it's a perpindicular force theta is 90 and you just get torque=radians x acell . in this case u change rpm to rad/s by algebra and then use each gear as a different radius to derive the acceleration possible by that gear and at what angle (rpm) you get max torque. then thru comparison of different acceleration values you find the point between two gears where you have the least acceleration difference. that's the dropout that occurs during each shift. so you optimal shift point is the point where you get maximun torque and minimal angular acceleration and velocity drop off. and you change that angle back to rpms to find the shift point. oh and all these calculations are done in Nm and Watts. off the tops of my head i know 746 watts is 1 hp but i can't think of the Nm conversion to ft/lbs. it's not neccessary however because you are looking for the angle( rpm). and yes i did leave out a lot of other info that u need but it's kinda hard to explain. but i mean the basic theory is drive to a high rpm where when you shift you are still high in the torque curve.

yeah like i said it's easier if you can show what you mean. i'm not good at explaining without tools.

[XDGT03]

:eek2:ok, you're too damn smart :hammer:

[tharptroy]

looks pretty basic to me. all you'd need is a dyno graph to do it. if someone doesnt beat me to it, I might do it for fun. unfortunately, not plotting the torque curve on the y=x line means that it will have to be entered on a point by point basis.

[Elantra2.001]

um basically in that example, since 1st gear is so low, you can go all the way to red line. Since the other gears multiply force differently, and by a lower amount than say first gear, the best shift point can be lower than redline. It depends on the torque curve of the engine and the safe speeds it can attain. With the low redlines on our cars, its likely that redline is the best shift point, but until its graphed like that i cant be certain nor do i feel like thinking about it anymore as i have enough physics and calculus to worry about on my own time thank you very much.

[seraph0503]

haha. yeah that goes for me too. i put in what i know without doing extra physics. btw don't be a chem engineer. it's rediculously hard and you put urself thru hell for four years. freshman year is a joke compared to now and my spring semester courses.

[only1db]

if i remember correctly our best shift point is at a bout 6000 rpms....torque is a function of the valves opening and closing...once you go past the point 6000 the vavles cannot open and close fast enough to keep up with the engine and you are no longer using the power effectively...i could be wrong though

[southpawboston]

first line of web page:

"To understand the material of these documents, I assume the reader have a firm understanding of Newtonian Kinematics."

uh huh. :eek:

[tharptroy]

I dont have the ability to do a fancy graph here, so I did it by hand on graphing paper.

basically, 1st gear-shift at redline, 2nd gear shift at redline, 3rd gear shift at about 6,000-6100 rpm.

i dont know any guy with an elantra who needs to shift past 4th in a race, so I didnt bother to graph it.

the torque doesnt fade off all that bad on the beta 2, giving it the ability to run to the redline in 1st and 2nd.

dyno chart used was evil 247's graph outta the archives, gear ratios were as follows:
3.62
2.05
1.37
1.06
0.84
FD:3.65
torque values are as follows:
__peak-481, 272, 182, 141, 112
redline-351, 194, 132, 103, 81

the writer was a foreigner, and inevitably their sentences dont quite add up. this being a technical document makes things alot worse. its really not all that hard, took me about half an hour to do it.

there are easier ways of accomplishing the things he did...just looks like he was after something to show a school teacher.

[skycam]

a simple way to find optimum shift point is to make sure that you fall on the torque peak after you shift so (this is just a basic idea of shift point)-- 1st gear 3.62 divided by second gear 2.05 times the torque peak 4800 = 8476rpm (redline)-- second gear 2.05 divided by third 1.37 times torque peak 4800 = 7182rpm (redline)-- third 1.37 divided by fourth 1.06 times torque peak 4800 = 6203rpm-- fourth 1.06 divided by fifth 0.84 times torque peak 4800 = 6057rpm. this is just a simple way to make sure that rpm don't drop under your torque peak. .02



hey just saw above post after i posted , mines not to far off kool

[only1db]

um....ok...so what is the optimum shift point for our cars?

[tharptroy]

there is no single optimum point. here's a quote from what I posted a second ago "1st gear-shift at redline, 2nd gear shift at redline, 3rd gear shift at about 6,000-6100 rpm."

[skycam]

1st to 2nd redline, 2nd to 3rd redline, 3rd to 4th 6200rpm, 4th to 5th 6000rpm.


ah hell shift in the red every time

[only1db]

you know whats funny is that the optimum shift point is right where the hesitation is!! LOL

[skycam]

that 4800rpm torque peak I took out of a magazine if you were to actually dyno and find out your true torque peak at the wheels my formula might be a little more accurate. oh well, it's a whole lot easier than the other formula but not as accurate, but everyone can do it.

[FordFasteRR]

well, I have smaller tires than stock... 50 series and I can stay in 3rd gear through the traps.. I dont even reach redline before I pass the traps.. that explains my low MPH ! LOL

:)