If a 3.45 diff is put into my EF GLi wagon, whcich is currently a 3.25 or 3.02 or something, what'll be the story with the gear changes if the stock ECU is kept?
I've read that they change gears at a certain speed, depending on throttle amount, so if that speed is say 40 km's for 1 to 2 originally and the car is reving at 3000 rpm, with the new diff, it'll change at the same speed, but the car will rev up higher? So at full throttle I'd probably hit the rev limiter before it wants to change? So an XR6 ECU is needed?

i dont think it will matter all the gear box ecu wants to know is engine speed, load there the main ones yes it might look at road speed but shouldnt stuff it up to much i wouldnt think, what happens if u pull out road speed from ecu?

yep he is right. Engin will decide if it has enough power to change gears and will do so accordingly. The gearchanges are organised directly by the RPM of the engin in relation to speed...the computer knows if ur going up a hill cos the revs stay constant and the speed lowers...it knows to change gear here...Having said this if you are driving at 5000rpm it will know it is more efficient to change gears depending upon how far you have your foot on the throttle...

anyway if the engin revs to the rev limiter while in D...it will force a gearchange.

ndy

Reason I'm asking is because of what I read in http://www.fordmods.com/phpBB2/viewtopic.php?t=512&highlight=wade

As an interesting workaround : Goven that the dash gets its own speedo signal (doesnt it? - it does on an EB).

Silicon Chip/jaycar will be releasing an electronic speedo corrector in Jan (Im told).

So... Change your Diff. Leave the exisiting drive gear in the gearbox so that the ECU doesnt know that anythings changed... and then put the electronic speedo corrector between the Sender and the dash and have it correct the speed.

Would also work the other way (and might appear smoother to the speedo too)

Nigel

look here http://www.fordmods.com/phpBB2/documents.php?doc=30

you need to get a grey speedo drive gear for $8 from Ford and the speedo and change up points will all be fine.