Diff ratio for bec?
 

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

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 !:D

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.

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

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

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

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.

The 3.38 and 3.14 are rare may be worth considering a Freelander diff at 3.2
Whilst Burtons do know Ford they don't know as much about BEC and they are expensive
Locostbuilders all the way
You can swap crown wheel and pinion as a matched pair to another Sierra LSD diff
I have never seen any Sierra LSD apart from 3.62, 3.64 or 3.92
Quaife ATB LSD can be fitted

I'd hazard a guess that Andy Bates would be a better person to talk to about BEC fitment for both road and track.

True, you could buy 2 Ford diffs and make a long LSD, but would you see change from £500 for a diff made up of 20-25 year old parts?

In that respect, a Freelander diff would be the viable option. BMW might be worth a look at; they made plenty of LSDs in several models that are long enough for a BEC. There might be fitment issues though according to another user on this forum who has tried it. It's worth looking at though IMO, but you might need custom driveshafts or modifying the rear suspension to take BMW rear hubs.

I once went out for a ride in a ZX9R engined car. I loved it, it made me want a BEC and I very, very nearly bought a donor bike a few days after. I put myself off when I looked at the additional cost and work that going for a BEC entailed, especially as I wanted an LSD too. I came to the conclusion that the best way to go was a BMW diff, but I would have had to go for BMW/MX5 hybrid driveshafts. Not cheap.

Pork chop is pretty spot on with his info.
Super7thheaven has a fair bit of useful info on sierra and Granada diffs.
My experience is this.
I had a Formula 27 with a Zx9 motor in it running 195/55/15 and a 3.62 sierra diff. I did try a 3.92 and it was awful to drive on the road . Revving its tits off for no speed. The 3.62 was a good compromise between speed and acceleration and was great fun except on the motorway where is was doing about 7k for 70mph in top gear. So I would say that having a more powerful engine you would want a ratio lower than 3.62 as porkchop said. The freelander diff is probably your best cheap option really. Also I don't think you really need an LSD unless you are going racing.

Or want to do neat donuts. And 'Elevenses'.