Im just wondering if i got this right, the higher the number (numerically) of the diff, the faster acceleration you get, but lower top speed? if so, with an r1 locost, would 4.27 go crazily fast before it hits 60 or so? i was wondering if it would be a good diff to use on my car Here, bearing in mind that i would be using it a little along the motorway, but mostly around towns and along b roads taking it out to the beach and such. would it make the engine too high revving to be useful at high speeds? i have spotted a scorpio being used as a test vehicle at my local fire sation, so could get one (probably) free. cheers,
joel

Acceleration would be faster - but so would changing gear, slowing you back down again.

IMO this diff is too high a ratio, most of the power you would struggle to put down and you are right in thinking it would bring down the top speed. The lower the number the faster top end you will get (theoretically) and the better mpg.

sounds like my kind of diff

My R1 BEC will get to 52 MPH in 1st, 73 in 2nd and 120 at 11750 RPM in 6th with a 3.62 diff and either 195/50/15 or 205/60/13 wheels and tyres.

This would change to 44 in 1st, 62 in 2nd and 102 in 6th with a 4.27 diff. R1s have a bit of over rev you you can comfortably do a 0-62 timed sprint without hitting the limiter.

It will be a bit rowdy on the motorway geared like that but if you plan to take it on a spring course where speeds are always below 100, you'll have a competitive car.

As Hellfire says, you'll gain in gear acceleration, but you'll be in the gear for such a short time that you'll not really gain much overall. I had a 3.89 in my Blade BEC for a while and although it felt quicker (mainly because the revs rise quicker fooling you into thinking its quicker), overall the acceleration compared to my mate's Megablade was identical with a 3.54 or a 3.89.