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Will gears without a tune damage the transmission?

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Will gears without a tune damage the transmission?

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Old 06-01-2011, 04:58 PM
  #11  
pdonket
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Yeah you won't have any spectacular grenading or anything going on. Your shift points will just be all messed up and the speedo etc will be wrong. But in any case, getting a tuner with gears is a good choice.
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Old 06-01-2011, 06:10 PM
  #12  
Red2002GT
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Why would shift points be messed up?
Just trying to figure out the logic.
I would think shift points would be controlled by rpm, and rpm would be read off the motor.

If gearing without tune would mess up shift points then wouldn't changing tire size without retune mess up shift points as well?

What information determines shifts, and what sensors provide that information?
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Old 06-01-2011, 06:52 PM
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Nuke
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Originally Posted by Red2002GT View Post
...I would think shift points would be controlled by rpm, and rpm would be read off the motor...
For a given RPM, the gear size programmed into the PCM is used to determine shift points. Without changing the gear size for the PCM, the shiftpoints will remain based on what the PCM thinks the correct point is. Although it's not a terrible mismatch, not retuning the shift points doesn't optimize engine power efficiently.

Originally Posted by Red2002GT View Post
...If gearing without tune would mess up shift points then wouldn't changing tire size without retune mess up shift points as well?...
Most tire size changes are minor impacts to the overall final drive ratio compared to the more-significant gear changes. Unless you're going about 1.5" or more higher or lower in tire O.D., it's not a big deal. Most tire size changes maintain the OE 27", give or take .5".

Originally Posted by Red2002GT View Post
...What information determines shifts, and what sensors provide that information?
Good question and even if I knew for the S197, it may not apply to your '02.

Last edited by Nuke; 06-01-2011 at 06:54 PM.
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Old 06-02-2011, 04:32 PM
  #14  
alkemist
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Originally Posted by Red2002GT View Post
What information determines shifts, and what sensors provide that information?
I believe it is written in the tune on when to shift. My auto up shifts at every 10mph mark (5th gear will be 50mph). It does not maximize the gear per say because an auto will never get close to redline, unless you drive it manually or I assume it's written into the tune to act that way.
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