I know this has probably been discussed before and let me apologize in advance. I have spent the last hour searching the forums but have not been able to find the right thread.

I own an '06 a/t Z. I am looking to purchase/install the 3.5 final drive. I originally wanted the 3.917 (as my '05 Mustang GT A/T has 4.10 fd,) but I have read that they require extensive custom work in order to properly install them on the A/T.

Some of the threads I have read stated that with the 3.5 gears, the a/t doesn't shift fast enough and bumps the rev limiter before shifting. This can probably be fixed with a proper tune. However, how do I get that tune if I decided to go with the 3.5 gears? With the Mustang, we just bought a handheld tuner and switched the final drive option to 4.10. I understand that with the Z, it is a bit more complicated. Any input would be greatly appreciated as this will probably sway my decision on the 3.5s either way.

 

Your best bet is to get an ECU reflash and get the rev limiter raised to 7100 rpm.

 

is there any other way I can tune the computer to know that the car has 3.5 FD, and shift accordingly? I'd really hate to have to raise the rev limiter and redline my car jus' to get the 3.5 gears workin' correctly.

 

It shifts without any problems at all =)
you dun have to do anything with it
the TCU, ECU will adjust accordingly
as long as you dun go beyond 3.53 FD ratio

 

I've never had any problems with mine not shifting. I drive in manual mode a lot though.

 

oh that's good... than maybe the guy I read it from jus' doesn't know how to drive...

What about the speedometer? Does that need to be recalibrated? Again... I have searched and looots of threads on it but they're all useless lol...

 

Speedometer is fine. Its not affected by gearing changes.

 

Thank you to all who responded. :-)

One last question: how was your MPG affected from 3.2 to 3.5? I understand that it depends on the way you drive but on average how much did you lose from the way you were driving pre-3.5?

 

I think mpg is very neglectable, notice that the g35x guys have 3.53 FD with their autos (they are a hundred + poudns heavier too), but I never see any complaining abt the mileage

For myself, I never have good mileage anyways..with the heavy right foot

 

Sorry to hijack your thread... I have been looking into the same pumpkin swap and have one question.

Will the cruise control still work with the 3.5 FD?

 

mine does,but ive heard from others it doesnt.