What parts I need to buy for changing 4th and 5th gears in Civic VTi (B16A2) transmission to Acura Integra LS ratio? Only countershafts and mainshafts? Or do I need other parts? Thinking to use it and osidetiger 12-Hole Fuel injectors for getting more confort in highway (REVing less) and also a little bit higher MPG.

 

You can change 5th gear really easily in your B16A2 transmission with LS parts, but changing 4th gear is a bit more complicated. Since the hub/slider diameter is smaller in the LS transmission compared to the B16A2 transmission, you would have to change both 3rd AND 4th gear. I would just change the 5th gear and leave the other gears alone.
Changing fuel injectors will not increase fuel economy. You will have to tune the car to maximize fuel efficiency at highway speeds.

 

Ok, so probably I'll change only 5th gear ratio. Which parts i need to buy? countershaft, and mainshaft? any other thing? I'll talk with a guy who sells and set Hondatas and also Chrome setuped chips for P30 injection to ask him about how to maximize fuel efficiency.

 

The part numbers for the Main shaft and Counter shaft gears are (23581-P80-000) and (23461-P80-000) respectively. Nothing else is needed.