Diff ratio for bec?

[Joelove]

Hi all, will soon be looking at purchasing an lsd for my build but not sure what ratio I should be looking for?

I'm fitting a 2004 cbr 1000rr engine, and it would be nice to be hitting a top speed of about 125-130mph.
Haven't got a clue how to work the diff ratios out so any help would be great!

Thanks in advance joe

[jason 82]

Try giving burton power a call on 0208 5189189. Burton are ford experts & I am 100% sure that they can sort you out ! I have done a lot of business with them over the years with my puma 1.7. There is nothing that they don't know about Henry's cars !

[Talonmotorsport]

You would do better asking the same question on locostbuilders as people on there have a lot more experience with bike engines going in both race and road cars.

[Joelove]

Ok thanks guys, ill Ask the same question on locost then and if no reply then ill give burton a tinkle

[PorkChop]

Why would you ask Burton, they do nothing with bike engines...

Anyway, there's a good Excel based gear ratio calculator over on LCB. There's ratio data for a CBR1000 already loaded into it, you would have to check if that covers the 2004 model.

Anyway, you would need a 3.14:1 ratio to get a 124mph top speed if you're running a Sierra diff in combination with 195/50/15 tyres, with a 70mph cruise at 6200rpm. That's the rarest ratio for the Sierra, were only available on the 2.3 diesel and command a significant premium over other ratios. Good luck finding a LSD version, I can't see Ford doing a factory LSD for an oil burner. This would leave getting something like a Quaife LSD then transplanting it into a standard diff, which would cost you the best part of £1k to do, Burton sell the Quaife LSD for £650, you'd probably have to part with £200+ for a complete 3.14 diff and add sundries and assembly costs on top.

If you have a Mazda diff, the longest ratio is a 3.6:1 which is found in a few Torsens and the Super Fuji diffs. Gives a top speed of about 107mph with a 70mph cruise at 7200rpm.

HTH

[jason 82]

I suggested burton as they know the diff ratios and could advise the best possible option. Burton have extensive experience in Motorsport, including rallying, so there would be nobody better to talk to than Burton Power.