What's a decent Diff Ratio for a 4spd box????
Discussion
The bloke who built my car in 1990 was (is ?) a Professor of Engineering at some university or other (forget ... Stoke ?). Amongst the many items of interest in the large folder that came with the car was a load of calculations by him WRT different diff ratios, different BHP, and the resulting top speed max.
If I remember (remind me if I forget) I'll dig out that sheet tonight and post the info. Can't remember what diff I've got, but my top speed is about 115 mph or so (theory, not had it above 105 yet)
If I remember (remind me if I forget) I'll dig out that sheet tonight and post the info. Can't remember what diff I've got, but my top speed is about 115 mph or so (theory, not had it above 105 yet)
3.54 is a bit long ....... You'll propbably want something closer to a 4.1:1 / 4.4:1 to get awesome acceleration and a decent top speed.
IF your g'box is a 1:1 final drive (should be), and you know the fitted circumference of the rear tyres, you can work out the theoretical top speed
Engine at 6000 rpm, propshaft doing 6000 rpm, diff ratio 4.1:1, then halfshafts/wheels doing 1463 rpm(6000/4.1). Tyre circumference 1.97m (estimated for 16" rims), so theoretical speed would be 1463*1.97/1000*60 = 173 km/h (about 110).
Easy math really.
IF your g'box is a 1:1 final drive (should be), and you know the fitted circumference of the rear tyres, you can work out the theoretical top speed
Engine at 6000 rpm, propshaft doing 6000 rpm, diff ratio 4.1:1, then halfshafts/wheels doing 1463 rpm(6000/4.1). Tyre circumference 1.97m (estimated for 16" rims), so theoretical speed would be 1463*1.97/1000*60 = 173 km/h (about 110).
Easy math really.
Discussing suitable diff ratios for a four speed i.e.direct top gearbox is not much use without knowing what rev limit you are imposing.
The idea is to choose a ratio which the car is just able to pull the rev limit, and that will be the top speed. If you were to then fit a 5speed box then the 5th gear would become an overdrive which means that it would NOT be able to pull the top speed but WOULD reduce the revs required to pull a cruising speed
John
The idea is to choose a ratio which the car is just able to pull the rev limit, and that will be the top speed. If you were to then fit a 5speed box then the 5th gear would become an overdrive which means that it would NOT be able to pull the top speed but WOULD reduce the revs required to pull a cruising speed
John
Phew, had me worried there for a second.
When I bought mine it had hoooooge heavy 16's on the back and 15's on the front. Ride was abysmal, handling was awful and the steering went completely to hell at about 80mph.
Needless to say I'm on 13x6 all round now and all is as it should be.
I've got Minators, they're sweet wheels; light, cheap and they look good. Speak to Jonny at BookATrack as he does a very good deal on them. £60 a 13x6 Minator in either Black or silver. £70 for a 13x7 but you only really need them if you are wanting to put down over 250bhp. Having all the same size makes rotating them easier also.
Yokes: depends what you want. 185x60 21/32R's are about £60ish each though if you are going to fit the 32's I strongly recommend that you make sure your oil system is up to it. For gooning; 539's are about £40 each and the ultimate airfield tyre. I get all my tyres from BaT.
>> Edited by juansolo on Wednesday 9th October 08:19
When I bought mine it had hoooooge heavy 16's on the back and 15's on the front. Ride was abysmal, handling was awful and the steering went completely to hell at about 80mph.
Needless to say I'm on 13x6 all round now and all is as it should be.
I've got Minators, they're sweet wheels; light, cheap and they look good. Speak to Jonny at BookATrack as he does a very good deal on them. £60 a 13x6 Minator in either Black or silver. £70 for a 13x7 but you only really need them if you are wanting to put down over 250bhp. Having all the same size makes rotating them easier also.
Yokes: depends what you want. 185x60 21/32R's are about £60ish each though if you are going to fit the 32's I strongly recommend that you make sure your oil system is up to it. For gooning; 539's are about £40 each and the ultimate airfield tyre. I get all my tyres from BaT.
>> Edited by juansolo on Wednesday 9th October 08:19
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