Adjusting SCT tune for auto trans

[acrbill]

There are adjustments for auto trans tunes on the SCT that I am trying to figure out. One is WOT and the other is pressure. What exactly will adjusting these values accomplish? I would like to take some of the harshness out of the shifts and perhaps have it shift at a higher RPM.

 

[Impetuous]

There are adjustments for auto trans tunes on the SCT that I am trying to figure out. One is WOT and the other is pressure. What exactly will adjusting these values accomplish? I would like to take some of the harshness out of the shifts and perhaps have it shift at a higher RPM.

Sounds pretty simple to me, one is how hard it shifts(pressure) and how high in the rpms(wot) which is actually speed(mph) if you noticed it.

 

[acrbill]

So the WOT adjustment is where it shifts during WOT and the adjustments are not RPM based but MPH based? Does anyone have shift point recommendations? I am going to have to make up an Excel worksheet to figure out RPM based on MPH in a given gear.

 

[Impetuous]

So the WOT adjustment is where it shifts during WOT and the adjustments are not RPM based but MPH based? Does anyone have shift point recommendations? I am going to have to make up an Excel worksheet to figure out RPM based on MPH in a given gear.

Well depending where the tuner set it up let's say it shifts from 1-2 at 7K i.e at 40mph when you look in the programmer screen is going to show 0 3 6 mph increments or decrement like 0 -3 -6 mph. So adding 3 would make it shift for example at 7.2K. Hope this helps.

 

[Impetuous]

Mine shifts at 7.2k and it came like that from VMP but I plan to do some testing at the track at different shift points.

 

[acrbill]

I found an online calculator Fatboy Raceworks » Graphical Transmission Gear Ratio Calculator. I plugged in the gear ratios, tire and final drive. You set the redline and it shows you the max speed for each gear. Its pretty interesting that small adjustments in MPH equate to large ones in RPM. My tune seems to be shifting at 7k RPM.

Another interesting thing I noticed when playing with the calculator is the 3.55 gear seems like a natural choice for the car.

With the 3.15 gear and a 7200 shift point you are shifting into 4th at 105 MPH which hardly seems ideal. With the 3.55 you are shifting into 5th at 120MPH which would work great for the bolt on guys who trap in the mid teens.

Its also nice that I have a set of 3.55s in the garage.

 

[Impetuous]

I found an online calculator Fatboy Raceworks » Graphical Transmission Gear Ratio Calculator. I plugged in the gear ratios, tire and final drive. You set the redline and it shows you the max speed for each gear. Its pretty interesting that small adjustments in MPH equate to large ones in RPM. My tune seems to be shifting at 7k RPM.

Another interesting thing I noticed when playing with the calculator is the 3.55 gear seems like a natural choice for the car.

With the 3.15 gear and a 7200 shift point you are shifting into 4th at 105 MPH which hardly seems ideal. With the 3.55 you are shifting into 5th at 120MPH which would work great for the bolt on guys who trap in the mid teens.

Its also nice that I have a set of 3.55s in the garage.

Depending on the size of the tire the gearing can change a lot, but I don't see the auto shifting into 5th at 120 with 3.55s but with 4.10s and 27" tire yes.
Use this gear calculator http://www.f-body.org/gears/ I know it's an f-body site lol but it works.

 

[acrbill]

haha. something is seriously messed up with the calc I was using.

Depending on the size of the tire the gearing can change a lot, but I don't see the auto shifting into 5th at 120 with 3.55s but with 4.10s and 27" tire yes.
Use this gear calculator http://www.f-body.org/gears/ I know it's an f-body site lol but it works.

 

[kdanner]

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[acrbill]

Yeah I heard that a few times. I will keep my eye on the shift points.

You need to remember that setting shift points is much like bird hunting, you have to lead your target. In lower gears where the acceleration rate is faster, you need to lead them more. The value that is being set is when to command the shift, not when it actually completes.

 

[Impetuous]

You need to remember that setting shift points is much like bird hunting, you have to lead your target. In lower gears where the acceleration rate is faster, you need to lead them more. The value that is being set is when to command the shift, not when it actually completes.

If I get this right you meant to extend the rpms in the lower gears?

 

[acrbill]

If I get this right you meant to extend the rpms in the lower gears?

I think he means that if your rev limiter is set at 7200 and you set the shift point at 7100 you run a chance of the trans not shifting in time to avoid hitting the limiter or just going higher than you want it to.

 

[Impetuous]

I think he means that if your rev limiter is set at 7200 and you set the shift point at 7100 you run a chance of the trans not shifting in time to avoid hitting the limiter or just going higher than you want it to.

Thanks for the clarification.