Technical one; possibly for Rohan?

[tower of strength]

I'm fitting a Scorpio MT75 in my car (1970 +2s) and based on comments from another thread I'm a tad concerned about gear ratios. I've been bashing a calculator for a couple of hours and I'm now thoroughly confused. Has any one got a formula where I can calculate the theoretical speed for each ratio assuming std diff and tyres? the ratios are as follows (not sure which set I've got at the moment!):

; 1st 2nd 3rd 4th 5th
2.0 16v;3.89, 2.08 ,1.34, 1.0, 0.82

2.3 16v;3.61, 2.08 ,1.44, 1.0, 0.82

I was led to believe i have the latter set.

regards

Mark

[bcmc33]

Why don't you ask msd1107 for his spreadsheet on the subject.

See "An evaluation of 5 speeds for the Elan" in the Elan section.


Brian Clarke

[tower of strength]

thanks brian

Mark

[alaric]

I've had a go at working out the speed. I've measured 10 inches from the floor to the centre of the hub on my car and doubled that for the diameter.

I've used: rpm / gear / diff * 60 * pi * diameter * 0.0254 / 1000 * 0.62137

Conversions are courtesy of google.

So that's: engine rpm -> rpm at input to diff -> rpm out of diff -> distance travelled per minute -> distance travelled per hour -> km per hr -> mph

There's almost certainly a mistake in there...

Sean.

[tower of strength]

I'll give that a go Sean, thanks!!

Regards

Mark

[tower of strength]

I wish I had your expertise with exel Sean, best i stick to GRP repairs!!!

Thats mighty impressive, thanks

Mark

[Rob_LaMoreaux]

Here is my speed calculater. It is currently set for my 3.77 rear end, semi close ratio gearbox and Michelin MX4 155/80R13 tires. I got the revs/mile for the tires from TireRack.com.

You can enter in you own gear ratios and such and see the results. It works great on the Elan and the Corvette.

Rob

[Rob_LaMoreaux]

Definately go with the 3.61/2.08/1.44/1 ratio set if you can. The other is just too wide for the Elan. Fitted with a 3.55 rear end it would be acceptable even if the jump from 1st to 2nd is bigger than I would like.

Rob

[tower of strength]

Thanks for your help and assistance guys,

I have had a play with various calculators, bits of paper and a couple of programs/spreadsheets (www.gearboxman.co.uk worked a treat) and the following conclusions can be drawn:

the std 'box has a tall 1st(no shit sherlock!!) and will do aprox 40mph at 6500rpm, on a 130/5, we have 38mph and my MT75. . . 33mph, 2nd for the Lotus 'boxes gives you 60mph@6500 rpm the MT75. . . .58mph. 3rd in the 4 speed - 86mph, the 5speed - 88mph and the MT75.....83mph, they are all the same in 4th and the Lotus box gives a theoretical 5mph higher top speed (150 against 145 for the MT75)

Seeing as the Twincam is a nice torquey engine I dont think 7mph at 6500 rpm is going to make too much of a difference to the driving experience. What will make the difference is the 700 odd rpm drop when 5th is selected at 80ish on the motorway.

The 5 speed conversion continues!!!