Hey guys just a quick question. Making a JDM more highway friendly with a longer ratio, could i just replace some gearbox internals or is a UK gearbox the only way to go?

 

i dont there is much difference between the 2 tbh. What is wrong with your current box on motorway journeys?

 

Oh really, No problem yet but with the JDM running a close ratio box you get stuck on the highway in 6th gear doing 70mph at 3500rpm. I am hoping a UK gearbox has longer ratios and therefor a lower rpm at the same speed.

Am i far off the mark here?

 

A UK box has a different ratio to a JDM, so yes they are different.
I also have a JDM bug sti and wanted to do the same.
To be honest your better off getting a UK box and rear dif other wise the Ratio will be different.

Hope this helps.

 

That helps loads mate. Will have to keep an eye open for one, might be a costly thing.

 

Only 5th and 6th are different to a UK box, you can get different cogs and the JDM boxes are better than a UK one (use different parts ) so it may be cheaper just changing 5th and 6th, though unless your having serious problems (and as ive said before, its ratio'd about 170mph) I wouldnt change it at all.

Tony

 

If the spreadsheet I did a few months ago is correct, then swapping 5th and 6th in a JDM box (with 3.9/1.0 JDM final drive) with those from a UK car will mean:

3000rpm
JDM 5th=54 6th=69
UK_ 5th=60 6th=77

3500rpm
JDM 5th=64 6th=80
UK_ 5th=70 6th=89

Top speed (8000 rpm!) is 205 rather than 184.

All based on 235/45x17" tyres, E&OE

 

Wow! Thanks for the help, cleared up loads you guys.