Looking to improve gear ratio (get lower RPM)

zoom33

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2005 Mazda 3, 2.3L manual transmission
Hi Everyone,
I am looking for a solution to change the gear ratio in my 2005 2.3 Mazda 3, particularly for the last gear to make it more of an overdrive. The car was purchased in the US with a stock 5-gear manual transmission but I subsequently changed the transmission to a 6-gear one from 2007 European Mazda 3 2.0 liter (gasoline engine). Overall, the swapped transmission is more pleasant to drive but the 6th gear - actually produces even slightly higher RPM compared to the last gear in the 5-gear stock transmission. I listed below further options I have considered. Any ideas re: Option 1 in particular will be much welcome. Of note is also that I am about to do a swap to the 2.5L Ford Fusion engine, so there will be even more need for better gear ratios.

Stock 5-gear transmission: main-4.105/I-3.307/II-1.842/III-1.310/IV-0.970/V-0.755

6-gear Euro 2.0 liter: main-4.388/I-3.454/II-2.059/III-1.392/IV-1.030/V-0.837/VI-0.717


OPTION 1 - SWAP THE 0.717 6th GEAR TO A HIGHER RATIO SET

A similar successful swap was documented relative to the stock 5-gear transmission: https://www.youtube.com/watch?v=yJPVmCzTayY

This is the least invasive/least costly option as I could keep the clutch (recently put a new one in) and driveshafts. I have no idea though how to research suitable donors for the 6-gear transmission. I guess Ford or Mazda family could be donors but how to make the next step?

OPTION 2 - SWAP ENTIRE TRANSMISSION TO Mazdaspeed 3 (MPS)
This is described here:
http://www.************.com/353-mod...d3-trans-swap-into-mz3-updated-9-14-10-a.html
A painful option involving changing many car components and in the end people report noise issues with the Mazdaspeed 3 transmission.

OPTION 3 - GO FOR OPTION 2 FIRST AND THEN SWAP TO MAZDA 6 DIESEL
This is described here:
http://**************************/f...aspeed-3-gear-ratios-change-85889/index3.html
Even more costly option than Option 2, although one that gives me more reliable transmission and lowest RPM.

I also considered M3 diesel but it is not actually an option as the transmission will not fit due to different engine block.

Thanks for help!
 
Since the 6th gear of the 6-speed is taller than the 5th gear of the 5-speed, yet engine speed is higher with the 6-speed, the 6-speed must have a shorter (greater reduction ratio) final drive gear set. Perhaps that can be changed, shifting the entire set of gears taller, which should be acceptable because the 6-speed has a wider spread of ratios (top gear is taller and bottom gear is shorter). Of course, there is the usual problem of finding another transmission which has a taller final gear set and yet is so nearly identical that those gears interchange.
 
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