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Discussion Starter #1
I just installed 3.55s in my 2011 V6 Automatic, and assuming the cars mpg calculator isn't thrown off like the speedo, I'm getting 24 mpg in the city, compared to 17-19 with my 2.73s. I also have a JLT intake, which seems to give me an mpg or two of efficiency.I haven't worn the gears in enough to feel comfortable going on the highway, but I'll eventually have that information as well.

I'm having trouble finding alternatives to a tune for recalibrating the speedometer - are their inexpensive speedo tools that are completely effective? Thanks in advance, oh, and hello I'm Justin.
 

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On an automatic you are SOL for any speedometer calibration other than a tune.

And the fuel economy readout is most definitely affected by the incorrect calibration, it thinks the car is travelling a lot more miles than it actually is.

And while your city mileage probably won't be lower with the 3.55's it for sure isn't 5-7 higher.
 

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How are the shifts with the new gears? Is it thrown off now with the different gearing? I also have an automatic and am really interested in swapping for 3.73s.
 

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Thanks for the info Ltngdrvr, I knew it was too good to be true. How should I go about convincing the dealership that a tuner is ok to use?

As for how the shifting is, it seems to pull through the gears much faster. I haven't been pushing it much but I can quickly and quietly here it shifting into 4th much faster than before.
 

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Thanks for the info Ltngdrvr, I knew it was too good to be true. How should I go about convincing the dealership that a tuner is ok to use?

As for how the shifting is, it seems to pull through the gears much faster. I haven't been pushing it much but I can quickly and quietly here it shifting into 4th much faster than before.
Ive had a mine BAMA tuned since march and have had no issues with the dealership (even for some warranty work with the clutch). You can always flash back to stock before you take it in anyways :bigthumbsup
 

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Thanks for the info Ltngdrvr, I knew it was too good to be true. How should I go about convincing the dealership that a tuner is ok to use?

As for how the shifting is, it seems to pull through the gears much faster. I haven't been pushing it much but I can quickly and quietly here it shifting into 4th much faster than before.
That is really good to know. So you don't HAVE to get a tune for it to operate...just affects the speedometer and odometer, correct?
 

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As far as the MPG gain is concerned, if it's totally linear, the difference between 3.55 gears and 2.73 gears is 1.30 greater multiplier of revolutions. And what happens when you multiply that by 19 miles per gallon? You get 24 miles per gallon. So, I would guess that the gains in town are a bit over the stock gears, but you'll probably get more of a ding on the highway than you'll get a gain in town.

That's what I figured the tradeoff to be: efficiency for acceleration/power :)
 

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That is really good to know. So you don't HAVE to get a tune for it to operate...just affects the speedometer and odometer, correct?
Unless the tune on an automatic is adjusted for the gears it won't shift or downshift at the correct MPH and the converter lockup schedule will be off.

Yes, it will still drive okay but the performance will be compromised.
 

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Discussion Starter #9
@ Bokeo - so I could get the tuner and convert the settings to stock before each visit and they would just assume that any previous flashes in my car would have been to recalibrate the speedometer if that's what I told them?

In regard to needing a tune for the gears to be functional, I am starting to see this may be true as well. Although I hear the car shifting quicker, the throttle is less responsive than when I had the 2.73s in just a few days ago. I was assuming this was because I haven't put the pedal to the metal, but it seems more likely that the tune would benefit the performance.
 

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On an automatic you are SOL for any speedometer calibration other than a tune.

And the fuel economy readout is most definitely affected by the incorrect calibration, it thinks the car is travelling a lot more miles than it actually is.

And while your city mileage probably won't be lower with the 3.55's it for sure isn't 5-7 higher.
Wait... Does this mean that even with a tune your odometer will climbing too fast if you go above 3.31? :scratchchin
 

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Wait... Does this mean that even with a tune your odometer will climbing too fast if you go above 3.31? :scratchchin
No, how did you get that?

Tune can be set for whatever ratio gears you run, then the speedo and odo will read correctly.
 

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No, how did you get that?

Tune can be set for whatever ratio gears you run, then the speedo and odo will read correctly.

That's what I originally thought, but the part about the gas mileage being off because of the mileage being off made me wonder.
 

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That's what I originally thought, but the part about the gas mileage being off because of the mileage being off made me wonder.
The part of the PCM that figures the fuel economy reads miles off the same sensor that the speedo does so if the speedo is off then the fuel economy readout will be too. And if you're manually calculating the mileage then that figure will be wrong too because the odometer is off too.
 
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