3rd gear flattens out at about 5000 RPM. This may be fine on a street car, but it's killing my track times. What is the best final drive to put in this car ('90 Civic)? Can I take a final drive out of another Civic? If so what years/models? What is the final drive ratio behind the D15B1 motor with the 4-speed? What is the final drive behind the D15B2 motor with 5-speed? Will the final drive out of the 5-speed car work in the 4-speed box?

Appreciate any help with this.

 

Forgot to mention that this is an SCCA ITC car.

Thanks