Attention: All Automatics With Rear end Gears Swaps


New Member
Jan 5, 2004
Chicago IL
I am considering doing this to my car, but im concerned about my gas mileage, and my rpms at highway speeds. I was thinking either 3.73 or 4.10s. But my dad has made me leary of doing it because of the gas factor, and the rpms on the highway. I really would love to have a neck snapping take off. People that have done it, what is your expeirence with performance, gas, and highway rpms?
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Performance is great, gas mileage actually goes up a bit in the city because you're actually in a higher gear at lower rpm's so it balances out what happens on the highway, for me atleast. If you're worried about gas that much get 3.73's. But for me atleast I would never give up my 4.10's for less gear.
Oh and by the way most of the time that guys say "Geez my gears cost me so much on gas now..." What alot of people forget is 99+ guys have to get a chip to correct there speedo's, and to get firmer shifts, and like me most if not all advance there timing witch means you have to use 91 octane. So really if you drive alot on the highways will it hurt yea. Is it worth it YES!!!!!!!!! And if you don't want it to be so bad don't advance you're timing.
If you are pre-99 then I can add to it. I ended up goin with 3.27's which gave me a good bit more acceleration (yet not as much as people who went with 3.73's or 4.10's) and my rpm on the highway is 2K@70mph. Mileage was the same as before too. Now that I've got a rebuilt tranny and new converter, my mileage is upwards of 30mpg with about half highway/half city. A higher stall converter will also give you the neck snap you're lookin for so you don't have to try to do it all with gears.
I put 4.10's on my 98 AODE. It does make a big difference in acceleration, but after awhile you get used to it, and the 4R70W is still a slush box for shifting.

My gas milage didn't suffer all that much really, despite running almost 500 RPM's more at 65-70 MPH on the highway. You'll lose gas milage anyway because you will be on it all the time! :nice:

As for the sloppy shifts, I put on a TransGo shift kit and love it. That's where the neck snapping starts to happen. It'll do me for now!

Make sure to leave NEGATIVE feedback on my Trader rating!!!! :D
Stock, I was at 1950 at 65mph. Now, I think I'm around 2400, maybe a little less.

The air/fuel mixture drops as you go up in RPMs though a little (more air), so that's why it doesn't hurt your gas milage as much.