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Diff ratio for bec?
Joelove - 17/9/13 at 10:19 AM

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

twybrow - 17/9/13 at 11:15 AM

Check out the 'Sticky' at the top of the BEC forum - or click here

This is an in gear speed calculator which you can use to play around with combinations of engine, diff, wheel/tyre size. Enjoy!

MK9R - 17/9/13 at 11:52 AM

3.38 if you are going with the sierra lump

Joelove - 17/9/13 at 01:30 PM

quote:
Originally posted by MK9R
3.38 if you are going with the sierra lump

So the lower the diff ratio the higher the top end?

dave_424 - 17/9/13 at 01:58 PM

quote:
Originally posted by Joelove
quote:
Originally posted by MK9R
3.38 if you are going with the sierra lump

So the lower the diff ratio the higher the top end?


Correct

MK9R - 17/9/13 at 02:13 PM

quote:
Originally posted by Joelove
quote:
Originally posted by MK9R
3.38 if you are going with the sierra lump

So the lower the diff ratio the higher the top end?


Go too low though engine won't top out. You'll see the speeds you want with a 3.38

doobrychat - 17/9/13 at 04:14 PM

I had a 3.92 in my bec which was only good for 110 top end.. changed it for a 3.62 because of the cruising rpm.. seen 126mph on my speedo (private land) and still pulls away nicely..go too lower diff then it will be more rpm screaming to pull away...

Joelove - 17/9/13 at 04:14 PM

quote:
Originally posted by MK9R
quote:
Originally posted by Joelove
quote:
Originally posted by MK9R
3.38 if you are going with the sierra lump

So the lower the diff ratio the higher the top end?


Go too low though engine won't top out. You'll see the speeds you want with a 3.38

3.38 it is then! Thanks guys

Brackers - 17/9/13 at 08:01 PM

I agree. I have 3.91 and whilst you can get the speed, in a BEC it's not great for cruising. Thinking of reducing mine over winter.