Crown wheel and pinion options

[Weavie]

I am rebuilding a 1997 Caterham 1700 Crossflow Series 3LC and I want it to be a good road/touring car, not necessarily for track days. Before the rebuild started, the engine would rev to 6000 rpm but, with the standard 4-speed gearbox, I always wanted to change up to give a better cruising speed on dual carriageways, etc. It has a Marina live axle which I have to take apart to determine the final ratio on the diff, but I am led to believe it might be a 3.6 to 1.
Fitting a 5-speed box means carving the body about which I am reluctant to do so can anyone please advise me on alternative diffs that might give the car "longer legs" at the top end? It is also fitted with a Quaife unit which will be serviced, although Quaife have said there is nothing that they can do to help me with my challenge.
Many thanks

[Weavie]

Have you fitted a 5-speed box into a narrow body Caterham? How easy/difficult is it and what gearbox would you use?
Steve

[Weavie]

Please excuse my ignorance but what is a type 9 5-speed box? How would I know it if i saw it?
Thanks

[Weavie]

Brilliant! I am on a steep learning curve with the Caterham so any help or advice is much appreciated. My last experience of taking cars to pieces and rebuilding them was a Mini Cooper 998cc that I used for restricted rallies in sunny Wales back in the 60s!
Thanks very much.
Steve

[Weavie]

Hi Downsman

Thanks for the advice. As you say, better to do it while it's being rebuilt
Steve

[Weavie]

I was told that by an ex-Caterham employee when I asked him some time ago. It would be great if it was a direct replacement. I am going to First Transmissions tomorrow with my current gearbox to put it alongside a Type 9 5-speed to spot the differences. I'll let you know how it goes.

[Weavie]

Sorry, the company is called First Motion Transmissions.