Ok here is my calculation. I know that this is all theoritical and could be different depending on traffic and weather conditions. I did the calculations based on a continuous 60mph. That is the average speed on the freeway in the Seattle area. At 6am most days that is the speed that I travel. I figured 25 miles per gallon average.
The current final drive ratio of the CSVT in 5th gear is 3.12:1. I know in the manual it says .77, but that is just the 5th gear itself and not including the ring and pinion gear. With the zetec ring and pinion the final drive ratio would be 2.95:1. With a 23" diameter loaded tire diameter you get a 72.26 tire perimeter.
63360in per mile * 72.26 = 876.83
876.83 tire rotations per mile.
876.83 * 3.12 = 2735.7 engine rotations per mile (Original)
876.83 * 2.95 = 2586.6 engine rotations per mile (New)
2735RPM = 1 Mile per minute = 60MPH
2586RPM = 1 MPM = 60MPH
148 engine rotations difference
25 miles per gallon = .04 gallons per mile
.04gpm/2735 = .000014625 gallons per engine rotation
148 * .000014625 = .0021645 gallons per mile savings
76 mile round trip to work each work day - 2 weeks vacation
250 workdays per year give or take.
19000 miles per year
.0021645 * 76 = .164502 gallons per 76 mile trip
.164502 * 250 = 41.13 gallons saved per year
41.13 * 2.50(average price/gallon in WA) = 102.81
So with the change I would save approximately 102.81 dollars per year.
Then I would also have the added benefit of being able to go 61.3MPH in second gear at hard limit.
I know I would have a little slower acceleration, but I plan on doing some engine upgrades in the future.
Enlarging the wheel diameter causes increase rotational Inertia, which means slower starts that are not there with just changing the FDR.
I feel that it is an all around better option to change the final drive to the higher ratio.
