will642
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| posted on 2/9/09 at 03:42 PM |
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bec what diff?
im building a locost with view to fitting a bike engine for hilclimbs and track use only what diff ratio is best im hoping to use a live axle if
possible.
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maxey74
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| posted on 2/9/09 at 04:03 PM |
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I think it depends on the engine and intended use. Hillclimbs should be fine with the 3.62 (I could be wrong, If I am I'm sure someone will
correct me!). For trackdays I suspect at all but the shortest tracks you may find yourself bouncing off the limiter in top on the straights on a
3.62... Again this may depend on the engine.
I have a busa engined Indy and started with a 3.62. This gave ballistic acceleration but was too buzzy for the road and probably wouldn't give
a high enough top speed for trackdays (around 120 top end). With such low gearing this problem is amplified as you get to the top speed that much
faster.
I have since switched to a 3.14 and it's probably a bit on the tall side if I'm honest, brilliant for cruising but the car has lost a lot
of it's brutal acceleration. I understand if you use a turbo'd bike engine then a 3.14 is perfect. 3.14 gives around 140mph top end
'apparently' 
I have since acquired a 3.38 (open) diff which I am going to have converted to LSD. Hopefully this will give me the best of both worlds. If it does
then my 3.14LSD will be for sale - watch this space 
I think the 3.38 and 3.14 don't come in the LSD variety as standard... again, I stand to be corrected! I'm sure some 'diff
master' will be able to put you (and me) right.
Cheers
Max
Forgot to mention. 3.38 and especially 3.14 are hard to find and cost a fortune. 3.62 are common as muck and cheap 
[Edited on 2/9/09 by maxey74]
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BenB
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| posted on 2/9/09 at 04:07 PM |
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Very much depends on the engine/gearbox and final drive ratios (obviously no final drive in a BEC)...
So you really need to know your engine redline and gearing....
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progers
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| posted on 2/9/09 at 04:14 PM |
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You have limited options with live Axle. The most common one used for BECs is a 3.54 English axle. Based on that ratio you can use R1's, blades
and GSXRs OK. Not ideal for Busa or ZX9/10 engines.
There are other options but none are as common as above. Basically you either match engine to the gearing you have or match gearing to engine.
You will have more options if you go independent at the rear and use different ratio's available from Sierra and Freelander diffs.
Cheers
- Paul
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r1bob
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| posted on 2/9/09 at 05:51 PM |
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i use a 3.54 in my r1 bec,, which i find ideal for hill climbs and short sprints, tops out around 120 mph on the rev limit.
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ginger ninja
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| posted on 2/9/09 at 06:12 PM |
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The 3.54 I believe is only found in ford escort MK1 and 2 RS versions ?
Becomming hard to find a good one unless you want to pay over a hundred quid. Also the 3.54 is the highest ratio ford made for the English axle. All
the retro/classic boys want these too.
The atlas axle ( fitted to capri ) is a couple of inches wider and a fair bit heavier, but higher ratios are available - again at premium cost.
I run a 3.54 in a locost with a ZX9 - it tops out around 105-110 mph (also depends on rolling diammeter of rear wheels).
For hill climbs your first choice is probably correct - English axle with either a 3.54 or higher (3.89 is most common at around 50 quid or less but
may be too low geared). happy hunting
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dmac
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| posted on 2/9/09 at 07:46 PM |
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I've got a carbed R1 with a 3.89 english, its fine for short tracks and the acceleration is phenomenal. I've not found the top speed yet
but it should be good for between 105 and 110.
It would get a bit wearing on long journeys though so it depends what you want the car for.
Duncan
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