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Dumb n00b question... shift kits vs. reprogramming

B

bobc455

New member
I see that it is a popular mod to put the trans-go shift kits. I totally understand the reasoning here, and will be doing this soon myself.

However, I thought that the computer also had settings for the shift time.... and that if you changed these settings in software, the computer would just change the pressure settings to shift faster.

Wouldn't these two changes essentially have the same effect?

If so, then why spend money on a shift kit instead of just changing the parameters?

And if you buy a shift kit, won't the computer try to counter-act the shift kit by lowering pressures and trying to achieve the setpoints in software?

Or am I just a dumb n00b asking a dumb question? (Don't worry, I won't be insulted)

-Bob C.
 


I probably will, but I'm more interested in trying to learn right now. I'm still relatively new to the Pontiac world and just trying to figure these things out.

Thanks!

-Bob C.
 
The only input I can offer is this since I haven't personally done tuning myself, just read up on it. A shift kit is modifying how the accumulators work in your transmission.

In a basic sense, an accumulator will take pressure being applied to a clutch or band fluid circuit and help regulate how the pressure is applied. The fluid presses against the accumulator piston, which in turn presses against the springs and "gives" to an extent depending on the tension of those springs. In a shift kit (I'll use the Transgo kit as an example), you install springs with different tension and spring rate to alter how the accumulator regulates or dampens the fluid pressure. There can also be shims which simply limit how far the accumulator can actually travel. I've probably dumbed it down quite a bit, but that's a short description if you will. A shift kit which deals with an accumulator will work the same general way in any automatic transmission

A tune on the other hand (from what I understand) is affecting what is commanded by the PCM and deals with overall line pressures and such. The transmission will compensate for a shift kit to an extent (really depending on internal wear and achieved shift times), but the overall effect will remain. Two transmissions, one with a shift kit and one with a tune, both achieving the same shift times will still feel different and wear differently due to how the pressure is applied in and out of gears.
 
Thanks, Nik - that helps me visualize it better.

nik12937 said:
The only input I can offer is this since I haven't personally done tuning myself, just read up on it. A shift kit is modifying how the accumulators work in your transmission.

In a basic sense, an accumulator will take pressure being applied to a clutch or band fluid circuit and help regulate how the pressure is applied. The fluid presses against the accumulator piston, which in turn presses against the springs and "gives" to an extent depending on the tension of those springs. In a shift kit (I'll use the Transgo kit as an example), you install springs with different tension and spring rate to alter how the accumulator regulates or dampens the fluid pressure. There can also be shims which simply limit how far the accumulator can actually travel. I've probably dumbed it down quite a bit, but that's a short description if you will. A shift kit which deals with an accumulator will work the same general way in any automatic transmission

A tune on the other hand (from what I understand) is affecting what is commanded by the PCM and deals with overall line pressures and such. The transmission will compensate for a shift kit to an extent (really depending on internal wear and achieved shift times), but the overall effect will remain. Two transmissions, one with a shift kit and one with a tune, both achieving the same shift times will still feel different and wear differently due to how the pressure is applied in and out of gears.
Click to expand...
 
when you do custom tuning you can change the shift times and transmission line pressures. I dont know exactly how the shift kit works, but when you change the shift times it will shift much faster. during normal driving have the shift time set to change fast will get annoying so most people only do it when entering power enrichment mode. I think .0125 Msec is the fastest you can change the shift time to. if I am going like 20 mph and I go wot I can break traction momentarily when shifting from 1-2, and so I usually turn off my traction control. turning up the transmission line pressure helps the shift firmness, but you can turn it up too high.
 


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