Ratio advice

[DrKai]

Having the type 9 rebuilt. Lots of aftermarket gear kits around. simple question if you could pick any 5 ratios what would you go for? Main deliberation is 1st as available ranges from 2.04 up to the standard 3.65. I have a rough idea but would like to get some opinions. 

More details: lightweight gt6, tuned 2.5l (will aim for around 160-180 bhp), likely 3.89 diff, for hooning around countryside at weekends, odd hill and trackday and I may do the 10min drive to work in it on ocassion but no long distance cruising. 

Thanks

Kai 

[Clive]

You need the long input shaft anyway. I would look for something close to the std GT6 ratio. Or the V6 ratio first (which is what I am using, power at the top end of what you are targetting, but a 4 cylinder 16V engine, so less torque at lower revs) Remember on a trackday, and indeed hooning, first gear is not really used except when pulling away, and that you will need to take care to avoid diff damage. Less of an issue once away from first (I have a T shirt)

Or get a caterham 6 speed version

[DrKai]

Thanks Clive hopefully the diff will be slightly less of an issue as will be using a quaife atb and I believe the 3.89 is the strongest cwp? Unsure what torque levels actually make this combination go pop tho? I did look at the six speeds and almost considered a second hand sequential flappy paddle job but decided it was a touch of lunacy too far 

[dave.vitesse]

For the wife's Gitfire I use a 3.63 recon diff and 185x70x13 on the rear. This gave a gearing of 19.3 mph at 1000 rpm in direct top. The Gearbox/overdrive was a John Kipping's special. Mike P I guess, with a 25% reduction this give 25.5 mph at 1000 rpm. Engine a 2.5 Litre with 125-130 bhp and 160 ftlb torque. Blown one recon diff after 20,000 miles which took out one of the Rotoflex couplers as well.

0 to 60 in 6 sec. Don't ask the top speed.  It would pull like a train at 1000 rpm in top and through the gears you had to watch the rev county to insure it didn't hit 6000 rpm as things happened very quickly. The point with the 2.5 is to use the torque. Get it into top as quick as you can. Great fun at the time.

I agree with Clive a load of low down torque can cause a lot of damage to the gearbox and the diff.

Dave

[rlubikey]

For me, the Type-9 has very short legs in 5th gear. Of course, it depends what you're using the car for, but on a motorway, lower revs make the car less harsh. I have a 3.27 diff and 25% OD in the Spit, and I'd still like something more. There's plenty of torque from the 2.5PI so I have no doubt it could pull something taller. Laycock did up to 33% for the A-type and D-type, but the tallest was only 28% for the J-type.

I don't do track days and I consider myself a "lazy" driver. When I eventually kill my close-ratio gearbox I'll go for a wide-ratio one. I think that Triumph realised these suit their long-stroke engines very well. And then, the only question is, do I stick with Triumph's "Small Car" box with 1500 Spit ratios plus OD (28% this time), or do I go for a Borg-Warner/Tremec T5 with its myriad ratio combinations, including some REALLY TALL 5th gears?

So there you have it; first think about what you use the car for and then ask yourself what sort of a driver you are.

Cheers, Richard