What Diff For Bike Engined Car

[Johnnybizzle]

Hi,

Currently building cbr 1000 engined roadster, i have been told 3.14 or 3.16 would be best bt theyre rare and expensive, would a more common diff like 7" 3.92 diff work or would i be limited top speed or poor accelaration,

Any advise appreciated, Higher ratio the better?

Regards Jon

[londonsean69]

A lot of people over on Locostbuilders are using the Landrover Freelander diff for BECs, as it's about 9kg lighter, or something like that.

Probably best to do a search over there as a lot more people are building a variety of stuff, including loads of BECs

A few links to get you started;
http://www.locostbuilders.co.uk/viewthread.php?tid=112553
http://www.locostbuilders.co.uk/viewthread.php?tid=118881
http://www.locostbuilders.co.uk/viewthread.php?tid=98806

[slimtater]

Sierra 3.38 suits mine perfectly. Just need to find one! (early 2.3D Sierras?)

[chriseyj]

Was told my diff was a 3.62 but think it may be a 3.92 once I checked out the code on the back. Don't think I'll be doing 70 very often unless I want bleeding ear drums and a wrecked engine.
Still won diff for £8.00 so will give it try, more worried about the rusty looking oil that came out of it while I was replacing the seals.
Chris

[Tilly819]

in answer to the eirlier question the higher the ratio IE 3.16 is higher than 3.92 i now that sounds od but it works like this

3.16 turns of the input shaft = 1 turn of the wheels
3.92 turns of the input shaft = 1 turn of the wheels

Thus to conculde
it depends what you want the 3.16 will give you better top end but shower acceleration and the 3.92 will give you better acceleration but will be slightly slower at the top end

Personaly i have a 3.92 since were i live there are mainly windy roads with lots of tight corners and ups and downs so i opted for better acceleration than top speed

its really down to what the car is used for and were it is going to be used, for instance if you were to take it tracking somewere like cadwell you would want the acceleration were as donnington you would want the top speed

hope this helps

have just reilised iv writen an essay

Tilly

[ozzy1]

I think that with an engine of 900cc then a 3.62 is much nicer to use everyday and the drop in acceleration is only slight as you will find that you will be doing approx 1000rpm less for the same speed as with a 3.92(this is what i found on a zx9 engine).
There was a company called kit fit who supplied a lot of ford stuff dont know if they are still around.
The guy that used to own formula 27,steve porter,started dealing in engines & freelander diffs,i think they were around 300 quid(ish) new.He lives in Stroud ,Gloucester,maybe worth a search on google etc,or ebay.
The sierra diff ratio is usually etched into the rear of the large gear if you remove the back cover plate.

[flyerncle]

Divide the number of teeth on the pinion by the teeth on the crown wheel and this gives the ratio : 1,Higher the number 4:1-5:1 more acceleration lower more top speed. We used to fit 4/5:1 in group 4 rally cars with LSD fitted.Point and squirt from corner to corner.
As Tilly say's you trade one against the other,swings and roundabouts.

[Johnnybizzle]

Thanks for the info probably try get a 3.62 off the world wide web

regards

[7ishNZ]

Nissan made a 3.5 ratio that was fitted to a R200 housing.. easy to get a viscous LSD to fit.

[snapper]

The BEC boys on Locost seem to like the 3.38 diff, I know for a fact that the 3.9 is to low, the 3.6 gives a top speed of 110 on most bike engines and by then its screaming like a nutter( dont forget the bike gearbox has a drop down ratio built in) and most bikes have rear wheels that are 20" diameter.
Some bigger bike engines ( the ones that rev to 10,000) are OK with a 3.6 but you are still screaming all the time.
Fit a 3.6 for IVA then find a 3.3 at your leasure