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Discussion Starter #1
OK posted same question in ztec performance they said to post here also.
I swaped my wife's wagon from spi to ztec, the auto tranny is going out, I have a perfect spi auto tranny, I know they use the same axles and filter kit, but do they interchange???????? I really don't want to pull it to find that it does not and have to do a rushed rebuild on a spare core.
Thanks for any help
 

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Token Engin-nerd
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if you have a xs4p code you have to use xs4p otherwise the 1s4p and 3s4p will interchange. The 3s4p has better clutches than the 1s4p. There was a change to the final drive ratio and the PCM tune between xs4p and 1s4p.
 

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FocusRush
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1,774 Posts
if you have a xs4p code you have to use xs4p otherwise the 1s4p and 3s4p will interchange. The 3s4p has better clutches than the 1s4p. There was a change to the final drive ratio and the PCM tune between xs4p and 1s4p.
back from the grave...

If I have an xs4p, and want to use the 3s4p, Do i just need to swap the ECU as well?

@illinipo
 

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Token Engin-nerd
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3,414 Posts
back from the grave...

If I have an xs4p, and want to use the 3s4p, Do i just need to swap the ECU as well?

@illinipo
I have since forgotten everything I learned about the trans part numbers, but if I said the final drive changed between X and 3, it will probably mess with the PCM. At best, the speedo and odo will be off. Not sure by how much. At worst, the N/D (engine rpm/wheelspeed) calculation will mess up the shift points completely, to the point that it would probably be undriveable.

TL;DR: Yes, but don't forget about PATS.
 

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The rebuilders say absolutely not to switch them, the slight difference in final drive creates PCM issues.
 
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