steve_m Posted November 18, 2003 Share Posted November 18, 2003 I've got a choice of diff ratios which give my car a top speed of anything from 118mph on 15" wheels to 144mph on 16" wheels. I doubt the car would do 144mph with the standard Hayabusa engine from what people have said and top speed isn't really important anyway. Is a shorter diff better so I use more of the gears but change gear more often or a longer diff so I change gear less ? What's the optimum point ? Thanks, Steve Quote Link to comment Share on other sites More sharing options...
Turbo Tommo Posted November 28, 2003 Share Posted November 28, 2003 The lower the final drive, the closer it will bring your ratios together which is great if you need to keep the engine on the boil, however they could be too close and then you are hampered by the number of changes you have to make. With a 'busa I guess you'll have six gears with a 1:1 top, so they'll be pretty close anyway, but maybe you need that to cope with the narrow power band and relative lack of torque to a car engine. So you can use all the gears when competing, you could identify the event where you will be going the fastest e.g. Aintree or just gear your car so it will pull peak revs when flat out in top, and work backwards from there. However if this makes first gear only good for climbing up walls, then youve defeated the object. I reckon you could do the 144mph gearing and still be ok on the track. This will make the car nice to drive on the open road aswell. Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 28, 2003 Share Posted November 28, 2003 Changing the diff ratio will not make any difference to how close the gears are together. If the engine drops by 2000rpm between gear changes with a 3.6 diff then it will do that with a 4.1 diff. You would be better thinking about gearing for the first gear rather than top. If changing the diff would make first so low that you have to change as soon as you start to move then you have made things to low. As you say you are unlikely to ever reach v-max then work out the best ratio for starting off as you already have a nice close ratio sequential gearbox that will take care of the rest. Quote Link to comment Share on other sites More sharing options...
Nick Algar - Competition Secretary Posted November 28, 2003 Share Posted November 28, 2003 Steve, I have got the 3.31 to 1 in my car which on a reasonably fast circuit like Croft means I nearly reach the rev limiter in 6th at 2 places on the circuit. With 21/7x13 slicks it works out at about 130MPH. However at some of the tight sprint cicuits, Thorsby and Scammonden I barley get out of 3rd. Overall I think it's about right. Nick Quote Link to comment Share on other sites More sharing options...
steve_m Posted November 28, 2003 Author Share Posted November 28, 2003 Thanks, I think I might change my 3.14 for a 3.38 then. I've got 16" wheels for the road and 15" for track, 130mph is quite fast enough and that will mean 1st gear runs out at about 55mph. Thanks Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 29, 2003 Share Posted November 29, 2003 sounds good to me Quote Link to comment Share on other sites More sharing options...
windy Posted November 29, 2003 Share Posted November 29, 2003 Changing the diff ratio will not make any difference to how close the gears are together Eh What school did you go to Quote Link to comment Share on other sites More sharing options...
timd Posted November 29, 2003 Share Posted November 29, 2003 Think Matt's talking about engine speed rather than road speed... Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted November 29, 2003 Share Posted November 29, 2003 What school did you go to How about you Quote Link to comment Share on other sites More sharing options...
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