UK DIFF
#4
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The U.K. car has a 3.9 front diff and a 1.1:1 dropper in the gearbox to make it 3.545:1 to match the rear 3.545.
Jap cars have usually 4.44:1 diffs front and rear or sometimes 4.11 and the transfer is direct. ie 1.0:1.
Do not do what Scooby Sport did for me and fit 3.9 front and 3.545 rear in a Jap gearbox. You will experience handling and breaking problems and eventually the centre viscuos coupling will burn out with the possibility of other gearbox damage as I experienced.
The advantage of running taller gearing ie 3.9's is that 4,000 rpm in 5th is 96mph approx instead of the previos 82mph (approx) on 4.44's However the downside is that acceleration in the gears will be a bit slower and you may need to change out of top more frequently for overtaking.....unless of course you add substantially to torque and power in which case, subject to your overall gearing you have a theoretical top speed on an STi of 191mph or on a WRX of 168mph.
Jap cars have usually 4.44:1 diffs front and rear or sometimes 4.11 and the transfer is direct. ie 1.0:1.
Do not do what Scooby Sport did for me and fit 3.9 front and 3.545 rear in a Jap gearbox. You will experience handling and breaking problems and eventually the centre viscuos coupling will burn out with the possibility of other gearbox damage as I experienced.
The advantage of running taller gearing ie 3.9's is that 4,000 rpm in 5th is 96mph approx instead of the previos 82mph (approx) on 4.44's However the downside is that acceleration in the gears will be a bit slower and you may need to change out of top more frequently for overtaking.....unless of course you add substantially to torque and power in which case, subject to your overall gearing you have a theoretical top speed on an STi of 191mph or on a WRX of 168mph.
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