For the horsepower, and motor size, a virtually stock LT1 gets good mileage, especially on the highway. If i put a 3:73 or even a 4:10 gear in the rear, i know it'll get worse, but how bad will the top end and the gas mileage get? Is it worth it on a car that you put just under 100 miles per week on?

 

Honestly i didn't notice any change in mpg when i changed my gears. I'm sure if I went out and did all highway on a tank that I would get better mileage with 3.23's but when doing all around driving, i noticed no change.

 

i went with 4:11's in my car and its awesome. They should have came this way from the factory...i prolly lost like 1-2mpg, but i dont care i got a 4cly beater!

for example
with stock 3:42's in 3rd gear at 35mph @ 2,000 rpm
with 4:10's in 3rd gear at 35mph the rpm will be 2,600rpm
it rasies the rpm 600 more from stock at whatever mph your at.
-4:10's increase torque by 20%
-Most people say on a 6spd, get 4:10's or nothing at all, 3:73's you wont notice much