Quote:
Originally Posted by deni
Hi Mister Towed,
Hope you don't mind me asking a question. I've read earlier in your thread that you have changed your differential and that you are currently using 3:27 ratio one (I am not sure if you have an overdrive gear box or not), and that you are very happy with it. My question is; which differential would be better in your opinion, 3:89 or 3:63 ratio, with a Spitfire 1500 engine and non overdrive, 4 speed gearbox?
Many thanks, Deni.
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Hi Deni, always happy to answer questions. Yes, I have a GT6 3.27:1 differential with a non-overdrive Vitesse gearbox. I went with that diff as I planned to drive the car long distances and wanted to keep the revs down at motorway speeds and achieve better fuel economy. The GT6 diff gives me the same gearing in top as overdrive 4th with the 3.89:1 Vitesse diff in place, but was a lot cheaper and easier than changing the gearbox.
I like the character it gives my car - it'll do 40mph in first but still pulls hard from 30mph in top, but bear in mind I have a 2 litre six under the bonnet. It depends what you want the car to do which diff you choose: Phil J started with a Herald 4.11:1 which gave scorching acceleration on the track but the car ran out of revs at 90mph and was too low geared for road use. He now has a 3.63:1 with overdrive but that's being turned by a mighty powerful motor (2.6 litre six with about 180bhp).
For your own car running a 1500, the 3.89 would give you slightly better acceleration through the gears but the 3:63 would give a good compromise between acceleration, (theoretical) top speed, cruising ability and fuel economy. I'd go with that if it were my car and it's cheap and easy to change the diff if you don't like the way it drives. Also bear in mind that the bigger wheels and tyres we fit raise the gearing and that you'll need to match the speedo to the diff you use - I have a GT6 non overdrive speedometer to match the 3.27:1 diff and the speed reading is almost exactly correct (the bigger wheels/tyres take out the universal 10% higher speed reading error).
Good luck, I'm sure you'll enjoy driving your car no matter what diff you end up with.
