Help with best diff ratio

[gibbo90-9]

Hi, I'm building a 1700 fast road xflow and using a Corsair 2000e box and was wondering what would be the best diff ratio to use. I'm more interested in acceleration than high top speed  (90-100mph would be fine) My car is a '65 Mk1 2dr Cortina, originally a 1200, I think the diff in it is a 4.1, could I use this? Any advise would be very helpful, cheers Dave

[jamster]

im about same spec as you regarding engine and box. i've just removed 4.1 as it was revving alot at 70  i think 3.7 is the better diff but quite hard to come by ive just fitted 3.5 as i wanted more of a cruiser hope this helps

[Vista]

You can use a 4:1 and I will give you good pick up.....but it isn't just your terminal speed that suffers,  you'll find your engine revving much higher than previous at any speed and whereas with  taller differential you may have been comfortable cruising at 75-80 on the motorway or dual carriageway, with a 4:1 it may only be 60-65.

I use a 3.54 and am very happy with it, a good compromise between the two is a 3.77 or 3.89

[gibbo90-9]

Thank you both for your advise. I will start searching for a CWP, cheers Dave