Gear Ratio calculation | AEM
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stm
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Gear Ratio calculation

how can we calculate the gear ratio in to the gear position input setup?

what the numpers in x and y axis represent?

transmission gear ratio is:

1th gear ratio:
3,50:1
2th gear ratio:
2,18:1
3th gear ratio:
1,52:1
4th gear ratio:
1,16:1
5th gear ratio:
0,92:1
Reverse gear ratio:
3,91:1
Final drive:
3,11:1
AEM_NS
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Joined: 06/06/2014 - 09:31
Gear Ratio is automatically

Gear Ratio is automatically calculated for you by the Infinity. It compares vehicle speed and engine speed together and gives you a ratio value. The Gear table sets gear position based on gear ratio. Adjust the gear ratio breakpoint values to fit a particular gear position.

AEM_BB
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Joined: 06/04/2014 - 11:53
First step is to set up and

First step is to set up and calibrate your vehicle speed sensor. This is done under Setup Wizard --> Input Function Assignments --> Speed/Frequency --> Vehicle Speed Input. Adjust the calibration (if necessary) so that vehicle speed reads correctly, verifying with GPS on a test racetrack, or on a dyno using roller speed.

Next, take a datalog of driving the car in all forward gears. You'll at minimum need to datalog [Vehicle Speed, Engine Speed, Gear Ratio, Gear].To avoid confusing yourself, begin from a standstill and shift up through all the gears in order, then immediately put the car in neutral and stop. You only need to drive in each gear for a few seconds, and do not need to rev the engine very high for this. Below is an example of a 5-speed car. Notice that the channel "Gear Ratio" steps down each time the car is upshifted, and remains constant in each gear, even as RPM changes. Also, note that the Gear value IS INCORRECT at this point, since the Gear table hasn't been set up.

 

Next, note the value of Gear Ratio in the datalog for each forward gear, like this (values below are from above example - this car was a 5-speed):

1 - 173

2 - 100

3 - 67

4 - 53

5 - 42

 

Next, input this data into the Gear table. You will have to work from right to left (backwards). NOTE that you are NOT editing the top values in the table (gear numbers) but instead the bottom values (Gear Ratio breakpoints). You can ignore values for 0 (neutral) and any forward gears that the car does not actually have (e.g. 6 and 7 for this example). The two rules for populating this table correctly are 1) you want to "window" the actual value for each gear, so that there is a little "room" on either side of the actual gear ratio value. This way, if there's some clutch slip, the Gear position is still calculated correctly. In order to do this properly, you will need to take note of not only the current gear you're working on, but also the NEXT gear, so you know how wide to make the window; and 2) make sure to not leave any values as you move from one gear to the next, e.g. if Gear 1 is 140/200, the high value for Gear 2 should be 139. This prevents the ECU from calculating a "halfway" gear value. 

Here is how the Gear table would be populated for the above example:

 

After entering these values, take another datalog, and confirm that the channel Gear reads correctly. Note the yellow Gear channel, incrementing correctly at each shift:

You can now use the input "Gear" for all sorts of things, like boost control, traction control, DBW throttle curves, etc, without having an actual gear position sensor.

Hope this helps!

Beau

 

kb58
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Joined: 10/29/2014 - 09:21
I had to redo the calibration

I had to redo the calibration after changing gear ratios and it was handy being able to easily find this (again). Thanks for making this a sticky.

Jvigocorp98
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Joined: 11/25/2018 - 09:20
i am having issues setting my

i am having issues setting my my speedo on my aem series 3 gear ratio shows 10000 and  i can not find out where to change it or ajust. i have been threw every page in the wizard and all settings and i can not seem to find out how to set it. my speedo reads perfect if you look speed up via digital but it will not  show mph under vehicle speed. i am not running wheel sensors or anything.

AEM_SB
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Jvigocorp98 , there are a few

Jvigocorp98 , there are a few things that could cause what you're describing. Can you post a calibration and datalog that shows the car driving in at least gears 1, 2, and 3?

makaveli200369
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Joined: 11/12/2018 - 12:32
Can you fix the screen shots?

Can you fix the screen shots? It shows an icon similar to the attachment is now missing. Thanks

AEM_BB wrote:

First step is to set up and calibrate your vehicle speed sensor. This is done under Setup Wizard --> Input Function Assignments --> Speed/Frequency --> Vehicle Speed Input. Adjust the calibration (if necessary) so that vehicle speed reads correctly, verifying with GPS on a test racetrack, or on a dyno using roller speed.

Next, take a datalog of driving the car in all forward gears. You'll at minimum need to datalog [Vehicle Speed, Engine Speed, Gear Ratio, Gear].To avoid confusing yourself, begin from a standstill and shift up through all the gears in order, then immediately put the car in neutral and stop. You only need to drive in each gear for a few seconds, and do not need to rev the engine very high for this. Below is an example of a 5-speed car. Notice that the channel "Gear Ratio" steps down each time the car is upshifted, and remains constant in each gear, even as RPM changes. Also, note that the Gear value IS INCORRECT at this point, since the Gear table hasn't been set up.

 

Next, note the value of Gear Ratio in the datalog for each forward gear, like this (values below are from above example - this car was a 5-speed):

1 - 173

2 - 100

3 - 67

4 - 53

5 - 42

 

Next, input this data into the Gear table. You will have to work from right to left (backwards). NOTE that you are NOT editing the top values in the table (gear numbers) but instead the bottom values (Gear Ratio breakpoints). You can ignore values for 0 (neutral) and any forward gears that the car does not actually have (e.g. 6 and 7 for this example). The two rules for populating this table correctly are 1) you want to "window" the actual value for each gear, so that there is a little "room" on either side of the actual gear ratio value. This way, if there's some clutch slip, the Gear position is still calculated correctly. In order to do this properly, you will need to take note of not only the current gear you're working on, but also the NEXT gear, so you know how wide to make the window; and 2) make sure to not leave any values as you move from one gear to the next, e.g. if Gear 1 is 140/200, the high value for Gear 2 should be 139. This prevents the ECU from calculating a "halfway" gear value. 

Here is how the Gear table would be populated for the above example:

 

After entering these values, take another datalog, and confirm that the channel Gear reads correctly. Note the yellow Gear channel, incrementing correctly at each shift:

You can now use the input "Gear" for all sorts of things, like boost control, traction control, DBW throttle curves, etc, without having an actual gear position sensor.

Hope this helps!

Beau

 

Jvigocorp98
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Joined: 11/25/2018 - 09:20
data log fileBrian Eclipse 60
Jvigocorp98
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Joined: 11/25/2018 - 09:20
here is the .itssn Brian
AEM_SB
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Thanks for posting the

Thanks for posting the calibration and log file, Jvigocorp98.  It looks like an important table is zero'd out in your calibration, let's fix that. Go to Layout >> Add Control >> 1D Table. Find VehicleSpeed [MPH] in the list, add that 1D table. Notice the numbers for the breakpoints (bottom row) and table values (top row) are [0.0 , 0.1]    Please change both to [0.0 , 1000.0]  for breakpoints and table values.

 

Then, go to the Input Function Assignments page in the wizard,  Speed & Frequency tab,  double-click Vehicle Speed Input.   Change the second dropdown (VSS Digital Input) from Disabled to Dig3/ Dig4 /Dig6 [Hz]  ... whichever matches the input you connected the ECU.  That should get some sort of reading for VehicleSpeed [MPH] , and you can adjust the Vehicle Speed Calibration number if the readings are too high or too low.

 

Hope that helps,

SB

Jvigocorp98
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Joined: 11/25/2018 - 09:20
after this is done i just

after this is done i just need to ajust in the wizard or do i still have to look up the values and input them as above? cause i dont see any sectio for the valves above to be able to set them. sorry for bring this issue to you but i have spoken with multiple tuners locally and no one knows how to set up this function on this ems.

lightspeed_32
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Joined: 08/19/2014 - 10:41
Note.  Gearratio is simply

Note.  Gearratio is simply rpm divided by vehicle speed. You can easily set up a spreadsheet to calculate the correct vehicle speed frequency factor if you know your tyre size, gear ratios and diff ratios. From these you can calculate the correct gearratio table inputs as it is simply a table of rpm divided by speed in each gear. Compare calculated to datalogged values and  goalseek a mph-frequency correction factor for the wizard input. Drive and compare vehicle speed to GPS. 

 

 

 

aolsvi1
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Last seen: 5 months 2 weeks ago
Joined: 05/31/2014 - 00:24
Got it sorted on our track

Got it sorted on our track racer, and set it up with the Racepak IQ3. Amazing stuff! Thanks!