Been debating on whether or not to change out the final drive gears in my 5AT. I have heard mixed opinions about the 3.91 gears so im wondering if i would be better off going with the 3.5. If im understanding correctly the 3.5 final drive is the same as the 6 Spd, basically. My main consern is that my car is my daily driver and i do not have another car to drive around all the time. Most of my driving is done on the high way so this is why im conserned. I have heard that with the 3.91 gearing i will be cruising at almost 4500 RPM doing 75MPH...is this right? I dont want to make my gas mileage horrible since all my driving is done on the high way. Would i be better off going with the 3.5 final drive gearing and will it improve my 0-60 and ET??? Also, how much of a difference in the 3.5 and 3.91 RPMS at 75 MPH??

-sean

 

I've got the 3.91 in my '05 5AT, didn't noticed much of a MPG problem but you will lose cruise control...

 

when you are crising on the high way lets say 75MPH what are your RPMs at?

Was your acceleration alot better?

 

I would have to check my RPM's, I don't pay that much attention. The accel is a lot better, it looses that 1st gear lag it used to have...

 

Will you do me a huge favor and go 75MPH and check your RPMs?

Also, have you checked your top speed?

 

i dont understand why you would loose your cruise control. that would be something that i def would not be willing to give up

 

and when the hell did you get a 13.86 sean?? now im really goin to have to step it up

 

Bro, 4500rpm at 75??? seems high...

I was on roadtrip this weekend and at about 90mph it was in the 4200-4600 range i think....(going off memory)

 

dude with a different final drive your rpms are goin to change drastically when cruising on teh highway

 

The final drive gears should affect your RPMs alot. Do you have gears in your car or do you have the factory set up?

sean

 

Havnt got them yet, considering them though. Just looking at the + and the -

 

^ HAHA!! I thought you said 3.90 i didnt see that you were talking about my 1/4 mile time. Yeah, i called you that night and told you i broke into the 13's look at my threads one of them has the slip!

-sean

 

My 68 BBC Camaro tachs about 3,500 rpm with 4.10's @ 70mph. That's a 3-speed TH400 with a 1.0 3rd gear final drive.

You shouldn't be anywhere near 4,500 rpm. Especially since the G35 5th gear is under-driven @ 0.0834.

John

 

Was it worth the change to the 3.5 gear... Money wise. What was the difference that you felt ion the car.