Eagle2000GT

4.10s are approximately 25% more gear than 3.27s (4.10/3.27=1.254). The higher gear allows you to get your rpms up faster. You reach peak power faster and your car accelerates faster (as long as you have the traction to get the power to the ground). You will have to shift sooner, much sooner. This is one of the complaints I have heard about 4.10s. You will only be in first gear for a brief moment before you have to shift to second.

At crusing speed your motor will rev 25% higher. If you are running at 2000 rpm at 70 mph then with 4.10s you will be running at 2500 rpms. Gas mileage on the highway will go down. Gas mileage in the city remains largely unaffected because you just drive in the next higher gear. Some have said their city gas mileage has gone up. It is hard to say how your gas mileage will be affected. It depends upon your city/highway ratio. If you do a lot of interstate driving, then gas mileage could be a drawback. Gas prices are not going to stay low forever.

If you intend to race the 1/4 mile, then you could be affected depending upon your other mods. You do not want to finish the race in overdrive. With 4.10s you will typically run out of gear around 105 mph. That means you've redlined in fourth gear (manual transmission) before you reach the finish line. Lightly modded cars are not affected. Supercharged cars are. That is why most people recommend 3.73s for supercharged cars.

If you put in 4.10s and don't like them, you can lessen their impact a bit by getting taller tires. If you go from a 245/45-17 tire to a 255/50-17 you will go from 809.9 revolutions per mile to 769.5 revolution per mile. This will have approximately the same affect of changing your gears from 4.10 to 3.90. By the way, 245/45-18 tires have exactly the same diameter (27.03") as 255/50-17 tires but 18" tires cost a lot more.

Attached is a tire wheel calculator:
http://www.1010tires.com/TireSizeCal...?action=submit