OzVMX Forum
Marque Remarks => CZ => Topic started by: jimg1au on May 03, 2009, 10:54:47 am
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hi
i have the chance to put a close ratio gearbox in my 1971 cz400.it is a 4 speed and is the same fitting as the std 4 speed 400 g/box.the bike will be used for dirt track only.i have a range of front sprockets so final gearing will not be a problem.
what do cz riders think on this option
cheers
jim
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Tis realy simple Jim, the engine must be designed around the gear box.Close boxes allow you to narrow the power curve and the box lets you keep it there. Normaly the only differences between close ratio and normal is first gear which is usualy taller. In the end what it will be used for is the determining factor.It's also possible to make 'corrected' gears for a fraction of the cost of kit boxes.
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the different ratios
1st Gear Ratio 1.846:1 (13/24)
2nd Gear Ratio 1.466:1 (15/22)
3rd Gear Ratio 1.18:1 (17/20)
4th Gear Ratio 0.95:1 (19/18)
wider ratio
1st Gear Ratio 1.846:1 (13/24)
2nd Gear Ratio 1.375:1 (16/22)
3rd Gear Ratio 1.00:1 (18/18)
4th Gear Ratio 0.85:1 (20/17)
in this case 1st is the same
and the cost is exactly the same i have to buy a new gearbox
cheers
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There isn't really much difference between those 2 boxes, except the GAP between first and second. The rpm drop on each change is about the same just a few 100 rpm lower. A 23T first gear will bring the gap down a fair bit, I think the wide ratio would make a faster DT engine.