I want to get my 3.31 stock gears out and want to put in some 4.10s. I am getting a tune from breenspeed but I think the 3.31 are going to hurt my performance. Should I change gears? Or keep the 3.31? I dont go to track but I cruise around town a lot and love the extra power. What kind of gain will be there with tune and 4.10s? My 2007 gt has 38,00 miles, Will bearing be ok? Rear END?
The ability to tune an otherwise stock 3V motor will net you somewhere in the neighborhood of 5-15 horsepower, likely in the 7-12 range.
The 4.10s are a great idea, but the really don't add power...but they sure make getting to 60 MPH a heck of a lot quicker and more fun!
The basic mods for any mod motored Mustang is K&N filter, midpipe, catback (or in your case 'axle' back) exhaust, shifter and gears. Those alone will make your Mustang feel much better.
With 38K miles, your original bearings should be fine.
Best of Luck and Welcome!
As already mentioned, gear don't add "power" but they do improve acceleration. In fact, steeper gears often show a small drop in power on a dyno (don't ask me why, I don't know), even though they show a marked improvement (a few tenths) in the 1/4 mile ET's.
Gears are essentially on of the seven simple machines taught in any physics class. They are essentially a lever that works as a "torque multiplier." It's that effective torque multiplication that accelerates a car easier.
Swithcing from 3.31's to 4.10's is almost a 25% increase in gearing. So, switching from 3.31's to 4.10's feels the same as the same car with 3.31's with 25% more torque (320 lb ft to 400 lb ft).