Hi, i have an rs gearbox, my top speed on 5th is 120!!! Now i do a lot of highway so i need longer gears for cruising at lower rpm. Do i have to change the whole gearbox, or could i change tge final drive in the diff? Whats the difference among these two options? Help me understand ,thanks.

 

simple solution is drop a 4:11 final drive in...HKS and several other make one--- I would think that's the simplest and least expensive.

 

Please help me understand what the final drive is and do, i try search but i cant find an explanation. Does it make every gear longer?

 

Yes.

It's like the large sprocket attached to the peddle on the bicycle.

 

Ok, so how do i know what size final gear i have? If this can help i have an rs gearbox, and top speed in 5th gear at 7000rpm is close to 120mph. From my research i belive i do have the 4.85 final drive...can someone confirm?

 

the final drive is the last drive from the gearbox. you make that longer and all gears will get more top end

 

Stock evo FD ratio is 4.53, when you swap to 4.11 gears(ring and pinion in transmission) the final drive is now "taller", meaning all gears are longer.

the way you get your FD ratio if you wanted to do the math is, Driven gear divided by drive gear, what this means is you would need to count the amount of teeth on the driven gear in which case would be the ring gear On the diff inside the transmission, divided by the number of teeth on the drive gear (pinion shaft that is located under first gear). This would give you your final drive ratio, in fact, every gear ratio is calculated this way.

if you upgrade your final drive to a taller ratio, your car will loose lots of responsiveness on the streets and part throttle, often times requiring a retune to make a bit more power to make up for the unresponsiveness of the car with the taller gearset.