iiyama
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| posted on 10/5/07 at 05:53 PM |
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Diff
NA hayabusa. Have a 3.38 open diff but am looking to change this for a quaife ATB, so should I keep 3.38? Or go for 3.14? Or is there a better ratio
that can be speced??
If its broke, fix it. If it aint broke, take it apart and find out how it works!
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imp paul
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| posted on 10/5/07 at 06:08 PM |
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re diff
i think with a busa 3.14 is more for your build but its up to you 
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wheezy
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| posted on 10/5/07 at 06:10 PM |
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If you are happy with the top speed you have at the moment stick with the 3.38.
If you want a greater top speed but less acceleration go for the lower ratio.
I would stick with what you have got giving you better acceleration as there would not be many occassions you would be travelling at 130mph + 
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OX
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| posted on 10/5/07 at 06:20 PM |
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i changed mine from a 3.14 to a 3.38 and find it a better allrounder.
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iiyama
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| posted on 10/5/07 at 06:26 PM |
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Cheers guys. Dont know what Ive got yet as Im still building!! 
Thanks for the input
If its broke, fix it. If it aint broke, take it apart and find out how it works!
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Catpuss
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| posted on 10/5/07 at 07:03 PM |
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One thing that I've been thinking of (I'm not sure how much its been covered before) but a bike engine is designed to carry about
250-300kg at speed with the main power band around 1/2 to 2/3 its rev range.
The point is, when choosing a diff, don't think car engine (big tourque and high oil pressure at low rpm) think more like a bike. From my
experience modern motorcycle engines generally have a 50-60K (these days, used to be about 30K ti 40K) life before _major_ work, but they are also
designed to be pushed rpm wise.
They have short stroke wide bores, hence high rpm and low tourque. The oil pump, e.t.c is designed for this sort of operation. Bike engines really
don't like being laboured.
On top of that, for road use, speed limits are not worth risking your licence over these days. Better to turn heads with them having enough time to
see WTF that F1 sounding car was than have a copper turn his head at your speed
On and finally, I'm 3/4 of the way down a bottle of Chianti so whatever I've typed above may not actually be in English 
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rav
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| posted on 10/5/07 at 08:42 PM |
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But...
bikes are geared for top speeds of 160-200mph ish, and have 6 close ratio gears to achive this, without needing the engine to pull through a huge rpm
range in any of the gears.
So change the final drive to give you say 120mph top speed (as you say, more than enough for traffic clogged road use) and you have something which
not only screams like crazy at normal cruising speeds but also has all the gears stacked up together. Useful perhaps if you were powering the car
with a 5hp Briggs & Stratton off tghe lawnmower, but pointless if you have a potent bike engine which pulls well across a wide rpm range.
Whilst there may be a slight acceleration improvement from having a low final drive, I 'm not convinced its worth it.
The bike engined cars I've built had fairly low final drives and became annoying - rapidly shifting through 6 gears at very close intervals,
then developing tinitus for the next hour of driving at normal road speeds, all in 6th gear.
Give it a tall final drive to make it more like how the bike designers meant it to be, I don't think you'll regret it.
ps I see your wine consuption and raise u one beer. Therfore nothing I say is to be trusted.
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ChrisGamlin
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| posted on 10/5/07 at 08:55 PM |
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With most bike engine installs, you're fairly limited in diff ratio choice simply because you need a top speed of ~120-130mph, if not to go that
fast as least so you can cruise in (relative) comfort on the road without buzzing along at 9k all the time. If you want to track the car you wil need
all that speed.
In the other direction, you'll not get much above 130-140mph with most bike engines because with the longest commonly available diff (~3.2:1)
you'll still run out of gears above that speed.
The exeception of course is chain driven middys which you can gear however you like within reason.
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Toady1
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| posted on 10/5/07 at 09:54 PM |
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well ive currently got a 3.64 open diff on mine from when it had the pinto lump in, is that going to be too tall a final drive for my 954 lump? ie. is
it going to make me cruise at 70mph at around 10k and have a top speed of only 100mph? Ive no idea??
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