scubascooby

I was recently stunned by the excellent fuel consumption that results when driving my Sport MY97 at 55mph following a Passat TDi.

I had looked into fitting a 6MT gearbox but decided it might be impossible due to the different clutches and the extra weight put me off.

So thinking laterally, would it be possible to change the internal ratio of 5th ? Some markets had different ratios and different final-drives so I wondered if a ratio from a different box could give a higher 5th ?

I think 5th on the Sport gives about 20mph per 1000rpm on the original 195/60R15, if so then 70mph is 3500 rpm.

Changing the Sport fifth from 0.871 to the Turbo's 0.738 would change a 3000rpm cruise from about 63 to 74mph on my 205/55 tyres. That's a 17% increase in gearing.

I guesstimate that could be worth 4mpg or about 40 miles on a tank. Over a year that would certainly add up to a nice saving, about £6 ever time you fill up.

Other advantages, less motorway noise, less engine wear, less frequent fill-ups.
Disadvantage, slower 5th gear acceleration.

Questions:
1. Is it possible to swap the 5th ratio in this way ?
2. How much would it cost to do ?
3. Would it be driveable afterwards or would the gap between 4th and 5th be too big ?

scubascooby

I've read that a common problem (? ) on Imprezas is that the nut retaining fifth gear had a habit of coming loose. There is a fix involving taking the back sections off the gearbox and tightening the nut all with the gearbox in place.

Does this mean that it might be possible to swap the 5th gear in tha same way ?

scubascooby

Does anyone know if this is possible ?

Would it help if I found the gearbox code ?