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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. I am not allowed to post links here but it can be searched under: Replacing 5th Gear & Synchro Ring on a 04-09 Mazda 3

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 under 'How-To: Speed3 Trans Swap Into MZ3'. 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 under 'mazdaspeed-6-mazdaspeed-3-gear-ratios-change'. 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!
 
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