going auto 4r70 with 3.90 rear, good?bad?ugly?

[Evil Bender]

I've got all the parts togather to do a 4r70 swap in my 03 Cobra. The rear is geared with 3.90's , is that too much gear ? too little ? just right ?for a daily driver? Any imput would be apreciated

 

[blackbeauty1]

it all depends on your goals for the car.
im running 4.10's with 29" tires and at 70mph see 2350 rpms, ad on cruise control at 80mph i get 20mpg on a 4400 # car.
the low gear is forsure fun to drive.

 

[Evil Bender]

I drive the car daily, dont realy care about MPG, just wondering if i should switch back too 3.55s

 

[blackbeauty1]

if you have 26" tall tires you want to go back to 3.55's
example: when i had the 3.55 my car would top out at 149mph, with the 4.10's im done at 130mph, thats at 6500rpms.
i need the lower gear to get out the whole, with a 600 pound lighter car i would suggest taller gears.

 

[Evil Bender]

thanks for the input. I've been thinking I should go back to 3.55s with the 4r70s .70 OD but the 3.90s realy helped my car get out of the hole withe the 3.90's.

 

[Digital]

3.55 is a solid gear. you'll enjoy it more after you get some more power though.

 

[Evil Bender]

Thats one reason I was thinking about a swap,Im putting a new engine in it as well .car mad numbers in sig with a 2.80 upper only. since i'll be adding a lower ,the power will be going up.

 

[BADASS03SVT]

street car on 26s,,,I would go 3.55 or 3.73

if your going to race on a 28" slick I'd keep the 3.90s

I would also suggest using the AOD gearset in the trans of possible. 4r 1st gear is a 2.84 and an AOD 1st is 2.40. the car will like the 2.40 much better