Overdrive

[m1tch]

Hey guys, this is another 1 of my random idea lol when I was talking to Prof about dragracing his FC he said that near the end of the 1/4 mile he had to change up again, meaning extra time to change up, I was just wondering if an old school overdrive unit could be used to overcome this and to make the gears that ever so slightly longer so you didn\'t have to change up at the end of the strip.

I also thought that if overdrive could be fitted it would also help with fuel economy as when cruising at 60 its at about 2,500 rpm, with an overdrive unit fitted that would of course drop to say 2,000 or even 1,500 using less fuel

This is just a thought so I dunno if something like this could be fitted lol

[pdtaylor18]

For the expense you might as well change the Diff and get some better gear ratios in the gearbox.  I have an auto diff on mine so be interesting to see what sort of difference it makes.  Theres not much difference but the gear change may come earlier or even later if at all.  Not sure whether the auto diff on a manual car gives just better top end stuff or lower down, somebody is bound to know on here just what the differences are.

[grinder]

errrrrrrrrrrrrrrrrrrrrrrrr..... ..... i have a link at work that tells you exactly what you need to know .. i will dig it out on Tues

[grinder]

found it :

Also consider that most automatic cars use a 3.9 rearend ratio while most 5sp cars use a 4.1 ratio. Convertibles should all have the 4.1. You can check the ratio by jacking the car up, taking it out of gear, mark the driveshaft in relation to the differential case, turning it slowly while obvserving the output shaft/axle (whichever one turns consistently). Count the turns and note whether it takes <4 turbs or >4 turns to complete 1 revolution, this tells you which ratio rearend gear you currently have. Keeping the stock 3.9 will result in slightly lower acceleration but slightly better mileage. Swapping to a 4.1 rearend gives normal acceleration but slightly poorer mileage and top speed. IF you do decide to swap the rearend to the 5sp one (4.1), be sure to keep the 4.1 (gray) speedo calibration gear in the tranny.

taken from : http://www.rotaryresurrection.com/2ndgen/tech_auto_to_5speed.html

[pdtaylor18]

There you go, knew someone would know.  Oh well thats my theory gone then for the cabs if they all have the 4:1 diff no matter if they are auto or manual.  Another way and maybe suited more to just the drag day is the size of the rear wheels, going to larger diameter overall changes the rear end revolution.  I really dont know what sort of size difference you will need to get what you are after.  Unfortunately it will also change the 1st gear start and you will need to rev it a lot more and a lot longer if you go bigger.  You could go smaller and get the gear change in sooner but that would mean another unnecessary gear change and therefore lost time.   Be interesting to see how much difference it will make.  At least this way you can change to your road wheels and drive it home.  I am just throwing info into the fire here to see what comes out at the end.  I used to do a lot of karting in my Germany days and I was forever changing sprocket sizes to suit the revs I needed to suit some courses..This is exactly the same as changing the rear wheel sizes to bigger or smaller diameter overall.  karting was easier as i used to rely on the rev clock to gauge if the gearing was right.  Hence the need for about 5 of each rear and front sprockets during the setup day.

[grinder]

the info i provided is from USA i think - so did they have S5 TII cabs - i dont think they did - so it could still be worth finding out !