This would be a real cool thing to have if one of you engineer types would be so inclined as to make one.
The idea would be to come up with an equation where X = torque and Y = time - or whatever, and then plot a graph for a given gear ratio.
I'm thinking, start with a good set of data points (especially important with a turbo). Multiply torque by your gear ratio, convert torque to linier force and force acting on the 240 mass to get acceleration. Plot this somehow in a graph so that it would display the torque curve.
An extra cool feature would be to see all 5 gears on 1 graph to see where the torque curves cross.
The end result would be a graph that would show acceleration in terms of time for different gear combos. Then we could see how we might lose acceleration here but gain it there.
Anyone care to take a crack at it or know of one?
Acceleration Calculator.
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hannibal
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There a program called CarTest thats similar to what youre describing. The version I have is prolly 10 yrs old, but theres a newer one out now.
http://www.cartestsoftware.com....html
EDIT: found the old version I have. Its a crappy DOS based program, but its gets the job done and its free...
http://www.cartestsoftware.com....html
http://www.cartestsoftware.com....html
EDIT: found the old version I have. Its a crappy DOS based program, but its gets the job done and its free...
http://www.cartestsoftware.com....html
Re: (IWannaS15)
Sweet. Funny thing, it shows the same 1/4 mile time regardless of what rear end I put in.
It says a 2700lb 240 with 300HP should do about a 13.3
It says a 2700lb 240 with 300HP should do about a 13.3
Re: (IWannaS15)
IIRC, the think the GTech shows a torque graph, if you go to the site its pretty cool, and has comp software.
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C-Kwik
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If you're just trying to find optimal shift points, there is an easy way to find them if you have a dyno of your motor.
With a torque dyno, scale the graph for each gear ratio. Make sure the Y coordinates are scaled so it shows torque at the wheels. Make sure the X coordinate is scaled so it shows wheel RPM. Then superimpose the images. Where each line crosses the next gear's torque curve is where you should shift.
An easier way is to simply use the HP curve. You will only need to scale the RPM axis(X-Axis) according to wheelspeed. Then superimpose the images on top of each other and each time the curves cross is where you shift to the next gear. Done correctly, either method will put the crossover points at the same RPM's.
As far as a program to do this type of thing, you'ld probably find a distance vs time graph to be much more useful when analyzing accelleration. A Speed vs time graph would also be a good option. It's doubtful that a torque vs time graph would be of much use though. Trying to use it to confirm any realistic end result would be useless as the math involved would be complicated.
With a torque dyno, scale the graph for each gear ratio. Make sure the Y coordinates are scaled so it shows torque at the wheels. Make sure the X coordinate is scaled so it shows wheel RPM. Then superimpose the images. Where each line crosses the next gear's torque curve is where you should shift.
An easier way is to simply use the HP curve. You will only need to scale the RPM axis(X-Axis) according to wheelspeed. Then superimpose the images on top of each other and each time the curves cross is where you shift to the next gear. Done correctly, either method will put the crossover points at the same RPM's.
As far as a program to do this type of thing, you'ld probably find a distance vs time graph to be much more useful when analyzing accelleration. A Speed vs time graph would also be a good option. It's doubtful that a torque vs time graph would be of much use though. Trying to use it to confirm any realistic end result would be useless as the math involved would be complicated.
If you wanted to get ridiculously accurate and complicated with it, you could do it this way.
Spend $15 to get into the drag strip.
Make 1st run using redline to shift all gears.
Alter the 1st gear shift point, but not the rest of the gears. Make a run. Continue altering until optimal gains are made.
Now, move to second gear. Repeat as stated above.
Now thrid, repeat.
Fourth repeat.
Get the idea?
There's NO WAY to find out for sure which is the best without just hitting the track. And it's MUCH cheaper to run your car all day at the track than it is to buy these programs and Gtech devices and crap.
Spend $15 to get into the drag strip.
Make 1st run using redline to shift all gears.
Alter the 1st gear shift point, but not the rest of the gears. Make a run. Continue altering until optimal gains are made.
Now, move to second gear. Repeat as stated above.
Now thrid, repeat.
Fourth repeat.
Get the idea?
There's NO WAY to find out for sure which is the best without just hitting the track. And it's MUCH cheaper to run your car all day at the track than it is to buy these programs and Gtech devices and crap.
Re: (KATwo40)
I'm trying to see how the car would perform with different rear end gears.
The feature that shows power in each gear does show different behavior from our 4.083 to a 3.69 with the former producing a spike of greater G force, but the 1/4 mile time comes out the same.
This actually seems to make sense because a taller gear should mostly just delay the shift points.
Try it.
The feature that shows power in each gear does show different behavior from our 4.083 to a 3.69 with the former producing a spike of greater G force, but the 1/4 mile time comes out the same.
This actually seems to make sense because a taller gear should mostly just delay the shift points.
Try it.
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C-Kwik
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Re: (KATwo40)
You don't need to account for any of that. The best acceleration always occurs when torque to the wheel is maximized. The gear ratios in the transmission are fixed so all the other factors make no difference for a given HP/TQ curve.KATwo40 wrote:One more thing...these programs and graphs superimposed are great, but to calculate acceleration rates, you'd also have to account for tire size, pressure, traction, tire friction, wind resistance, air density (since it effects wind resistance), etc.
The exception to this is during times when tires are slipping, but that should be momentary and usually only off the line. It also would affect the shift points, unless you have enough power to be spinning tires every gear change(Ford GT-TT anyone?) Calculating it would be quite difficult as well, as there are too many factors that contribute to this.
Perhaps a drag slick that expands with speed might affect this, but would still be hard to calculate without knowing the variable ratio rates and factoring them in regardless of what you are trying to calculate. And frankly, since the ratio would be speed based, the shift points really shouldn't change either.
^^^ To calculate raw gear acceleration data, yes, but to calculate vehicle actual acceleration data, you WOULD need all that. As your speed increases, so does wind resistance, along with many other variables that would affect actual acceleration.
When I posted that, I didn't realize he was looking for only a gear ratio calculator, as opposed to an actual vehicle acceleration / speed program.
When I posted that, I didn't realize he was looking for only a gear ratio calculator, as opposed to an actual vehicle acceleration / speed program.
Re: (KATwo40)
Acceleration only. But not acceleration for just one gear and one small time window. Reason is, a taller rear would be nice if it won't hurt acceleration durring every day goofing off.
My car will be turboed soon. I'll see how she rides. I'm also considering where I'll be in the power band when I need torque. Clearly, a guy with a 3.69 rear end cruising in 2nd at 4000 rpm is going to pull ahead of the 4.08 in 3rd at 2000 rpm. The taller gear gives up some down low, but gives it back up high.
I think the program is correct that the 1/4 mile time remains constant with only the time between shifts changing.
My car will be turboed soon. I'll see how she rides. I'm also considering where I'll be in the power band when I need torque. Clearly, a guy with a 3.69 rear end cruising in 2nd at 4000 rpm is going to pull ahead of the 4.08 in 3rd at 2000 rpm. The taller gear gives up some down low, but gives it back up high.
I think the program is correct that the 1/4 mile time remains constant with only the time between shifts changing.
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C-Kwik
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A taller final gear would only increase the potential for top speed and perhaps save a little gas. Overall acceleration will still be similar because the average overal gear ratios you will see in a 1/4 mile won't change by much. First gear speeds is the most highly affected area in terms of acceleration when a rear gear is changed. The rest will balance out. In the case of a taller rear gear, each lower transmission gear will overlap into the portion of the next transmission gear's vehicle speed range(from the original rear gear). This means the 1st gear will be able to provide a bigger torque multiplication at the overlap speeds. but the next gear will see less torque multiplication than before. But that next gear will provide more torque multiplication than the next gear. This continues through every pair of gears.
The opposite is true of lower rear gears. again, 1st is affected the most since there is a lot more torque multiplcation. But you'll hit a lower speed at redline which means you have to change to a lower torque multiplication gear at a lower speed.
For the sake of simplicity, I'll use some unrealistic numbers. But this should show, in essence, what a rear gear change essentially does.
Lets say we have 2 trannies:
Gear #1 #21st 8 162nd 4 83rd 2 44th 1 25th .5 1
If we were to assume the same rear gears, transmission#2 would accelerate slightly faster due to the lower first gear. But the last 4 gears would have the exact same rate of acceleration as the first 4 gears of transmission#1.
We could then take transmission#1 and apply a 2:1 rear end gear and again, when you compare it to transmission#1 with a 1:1 rear gear, the result is a faster 1st gear, but the same acceleration as the 1:1 gear after 1st gear. So other than the jump off the line, the car doesn't ulimately accelerate significantly faster for having a lower gear.
In reality, the overall ratios would probably never line up like that. But if you were to find more of an average line through both torque curves in relation to vehicle speed (it will look somewhat like a staircase), they will be very close. This indicates that the overall acceleration will not see a big change.
To sum up, lowering a rear gear serves 2 purposes. In drag racing, it allows you get a bigger holeshot. This may equate to no more tha n a couple of tenths at best, but in a heads up race where you're not running out of gear before the end of the race, it can make the difference.
In an autocross, for a lower speed autocross, where you might be dipping too low in the powerband in 2nd gear(most autocrosses can be completed in nothing but 2nd gear) and not seeing much in the upper RPM's of 2nd, it can help you power out of turns better. This can be true to some extent on road courses as well if you're finding you feel like the gearings too high coming out of many corners or perhaps you run out of gear before you hit some turns(you might want a higher gear for this).
Higher gears are usually used to either decrease highway cruising RPM or if you run out of gearing trying to hit a top speed. Occassionally, you might see a taller gear used for drag racing when 1st gear is so short and the car so powerful that you shift too soon after launching. IIRC the JUN drag S14 hit something like 70 mph in 1st gear. But when you're reaching 600+ HP in a stripped out lightweight drag car on slicks, shifting twice to hit 70 mph may take longer than running a tall gear and launching hard and not having to shift until 70 mph.
The opposite is true of lower rear gears. again, 1st is affected the most since there is a lot more torque multiplcation. But you'll hit a lower speed at redline which means you have to change to a lower torque multiplication gear at a lower speed.
For the sake of simplicity, I'll use some unrealistic numbers. But this should show, in essence, what a rear gear change essentially does.
Lets say we have 2 trannies:
Gear #1 #21st 8 162nd 4 83rd 2 44th 1 25th .5 1
If we were to assume the same rear gears, transmission#2 would accelerate slightly faster due to the lower first gear. But the last 4 gears would have the exact same rate of acceleration as the first 4 gears of transmission#1.
We could then take transmission#1 and apply a 2:1 rear end gear and again, when you compare it to transmission#1 with a 1:1 rear gear, the result is a faster 1st gear, but the same acceleration as the 1:1 gear after 1st gear. So other than the jump off the line, the car doesn't ulimately accelerate significantly faster for having a lower gear.
In reality, the overall ratios would probably never line up like that. But if you were to find more of an average line through both torque curves in relation to vehicle speed (it will look somewhat like a staircase), they will be very close. This indicates that the overall acceleration will not see a big change.
To sum up, lowering a rear gear serves 2 purposes. In drag racing, it allows you get a bigger holeshot. This may equate to no more tha n a couple of tenths at best, but in a heads up race where you're not running out of gear before the end of the race, it can make the difference.
In an autocross, for a lower speed autocross, where you might be dipping too low in the powerband in 2nd gear(most autocrosses can be completed in nothing but 2nd gear) and not seeing much in the upper RPM's of 2nd, it can help you power out of turns better. This can be true to some extent on road courses as well if you're finding you feel like the gearings too high coming out of many corners or perhaps you run out of gear before you hit some turns(you might want a higher gear for this).
Higher gears are usually used to either decrease highway cruising RPM or if you run out of gearing trying to hit a top speed. Occassionally, you might see a taller gear used for drag racing when 1st gear is so short and the car so powerful that you shift too soon after launching. IIRC the JUN drag S14 hit something like 70 mph in 1st gear. But when you're reaching 600+ HP in a stripped out lightweight drag car on slicks, shifting twice to hit 70 mph may take longer than running a tall gear and launching hard and not having to shift until 70 mph.
Re: (C-Kwik)
Yes, thank you. This is what I suspected. So, for a turbo 240 approching 300HP and driven on the street as a fun sports car, would a 3.69 from a Q45 be a good rear end gear?
I'm thinking it might be nice, but I'll probably just get a helical and keep my stock gear.
I'm thinking it might be nice, but I'll probably just get a helical and keep my stock gear.
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C-Kwik
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I'd probably finish the motor upgrades you plan and determine if you need a taller gear ratio at that time. If you find mroe than enough power in 1st gear to get off the line and if you feel like 1st gear almost seems pointless, you might consider upgrading. You would see a 10% increase in vehicle speed at redline in each gear and also a 10% decrease in torque. Under boost, you probably won't be bothered by it much, but if your boost threshold is a little, you'll probably notice the 10% deficiency before you get boost.