I have a Type R V5 and just changed the engine. (2.5) This engine rev’s to 7000 so decided to change diffs for longer legs. Had 3.9 front diff fitted and a diff and shafts from a JDM STI 7. Is this right?
Thought I would have speeds of :

STi 5/6/P1 Gearset and std uk diffs (3.9):

Maximum Speed per Gear:
1st: 40.7 mph
2nd: 68.4 mph
3rd: 99.3 mph
4th: 132.5 mph
5th: 174.5 mph
Taken from an earlier thread.

But I find that at 3500 rpm I am doing 72 mph in top (5th) This = 144 mph @ 7000 That’s no where near the speed shown above. The speedo seems to be reading low (about 4-5 mph at 70 mph) so used a GPS and get my figs. Where have I gone wrong?

 

Stupid Boy, Low Ratio Gearbox

 

Surely if you have UK front diff, you should have UK rear diff, not JDM....??

 

Hi Ron M8.

All the 6 speed diffs are now 3.9's which is the same as UK diffs.

Been offered a deal with ScoobyClinic for a 6 speed box. To good a deal for me to refuse. Oh well its only money.