Change gearbox transmission ratio

[rozo]

Hello,

I have Lancia Lybra '02 2.4 jtd 150 ps and at about 120 km/h I have about 2500 rev/min what makes the engine loud and it needs quite a lot of fuel (6l/100 km on average). That's why I would like to change the gear's transmission ratio by about 20-25 %.
Can anyone advise me where to get the gear cogs?

[some_other_dave]

No idea for a Lancia. But have you considered looking into larger wheels and tires? That will change your overall effective gearing by the percentage difference in diameter between the old tire and the new.

-soD

[rozo]

I have considered that. I could gain about 3%, maybe 6%, larger wheels/tires would not fit in the car.
I have also considered changing my gearbox to 6 gear from alfa romeo (lybra has no 6 gear version) but even the used 6 gear gearboxes are pretty expensive and I could gain only about 10% rpm.