So I got my JLT CAI and Tuner in the mail today and as I was reviewing over the Custom tune info sheet, I noticed that under gears I selected "Stock". Not really thinking that the 3:55 gears were optional that year, I left it with "Stock". I PM'd Chris at AM to see if I need a new tune but am wondering if the tune is for 3:31 gears, other then my MPH being off, would there be any other issues? Also, does anyone know how far off the MPH might be?

 

If you have an auto, the shift points will be off and thus not shifting correctly. If it's a manual, should just be the speedo off. Again, if manual, you can adjust with your hand held and long term just have them update the tune for you since it's free.

 

What alkemist said.

 

sounds good. Thanks guys. Yeah its a manual so I should be good other then the speedo. Will get an updated tune. Still gonna hopefully have time to install it tonight.

 

Hmmm. Would the 3.31 gears be the base on a 2006 GT also, or 3.55? I'm pretty sure that the previous owner of the car didn't change them (as I get >=25mpg hwy @ 70mph), but it doesn't say on anything that I got w/the car, including the window sticker. No optional upgrades were listed. FWIW on Forza III for XBox they list the default for the '05 as 3.55, but I'm not sure how much I'd trust that. Just curious, if anyone knows that'd be great. Thanks.

 

I know the 3:55s were an option for the manual starting somewhere around the 2007-2008 year for the manual. Before that they were standard in the 5 speed. As far as I know, 3:31s were the gears you could get in the autos.

I know I have the 3:55s because of the code listed on the door panel on the driver side.

 

Yep and there should also be a tag on the rear diff indicating the gear ratio

 

If it's just for the gears, you don't need an updated tune. You can adjust that yourself with the handheld.

 

As Alec stated, you should see a sticker on the rear differential indicating the gear ratio.

 

yeah its just for the gears. After the install today I will upload the tune and see about adjusting it. I know basically how to upload the tunes but I'll have to look into how to adjust them....