5 replies to this topic

[rockstar]

Hello has any one used a standard close ratio box in competition before. If so how did it do on reliability.

Did you go from standard to sccr or visvera if so what were the differences like.

[Cooperman]

For Endurance rallying a standard transmission is part of the regulations, as is a standard engine. Reliability is not the issue.
With a competition car you build the engine and transmission as a complete unit to suit the application. When a hotter cam is used it is necessary to have closer ratio gears to keep it in the optimum power band as determined by the head and cam (and the other bits like inlet, exhaust, distributor, etc). Then a lower FDR is needed as well.
So far as I know there is no 'standard' proper close ratio box, unless you mean the slightly closer ratios of the original Cooper, Cooper 'S' and 1275GT and with a reasonably standard cam & head those boxes worked fine.

[rockstar]

Ok, so if you have a big powered A series such as a turbo charged car with a large powerband am I right in thinking close ratio boxes are not needed as much as say a n/a car with a smaller powerband.

 

would you say that a helical box is as strong as a s/c box

[adamg1380]

I run a standard box for sprints & hillclimbs, but I have a cam to suit (swiftune SW5, fast road cam really) so I have a wide enough power band. With a set up like that you have a lot more choice of when and where to change gear. If I go for a CR straight cut (probably dog) box at the same time as a hotter cam, although personally I think anything beyond a 286 you lose in flexibility what you gain from more peak power.

[Cooperman]

In theory a helical gear is stronger than a straight cut gear as the root area of a helical tooth is greater then with a straight tooth. The advantage of SC is that they are cheaper to manufacture and it is thus possible to make a wider choice of ratios. However, with the Mini the only true close ratio gears are the SC ones so when fitting a cam with a narrow power band SC CR gears are the only option now available.

[mk1coopers]

ST did do a proper helical CR gear kit, I've got one fitted to a car, but the chances of finding another are minimal, I had to make one good set out of two, and the car is not used for competition work. With the SC gears you get slightly less transmission loss, and less sideways shearing force, which makes them (usually) more reliable with bigger power, and you get a better ratio choice, it just depends on if you can put up with the noise, I find that at 70 there's so many other noises one more doesn't make a difference !

Edited by mk1coopers, 05 June 2013 - 05:24 AM.