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Technical one; possibly for Rohan?

PostPosted: Mon Nov 27, 2006 6:22 pm
by 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

Re: Technical one; possibly for Rohan?

PostPosted: Mon Nov 27, 2006 9:25 pm
by 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

Re: Technical one; possibly for Rohan?

PostPosted: Mon Nov 27, 2006 10:40 pm
by tower of strength
thanks brian

Mark

Re: Technical one; possibly for Rohan?

PostPosted: Mon Nov 27, 2006 10:54 pm
by 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.

Re: Technical one; possibly for Rohan?

PostPosted: Mon Nov 27, 2006 11:01 pm
by tower of strength
I'll give that a go Sean, thanks!!

Regards

Mark

Re: Technical one; possibly for Rohan?

PostPosted: Mon Nov 27, 2006 11:53 pm
by tower of strength
I wish I had your expertise with exel Sean, best i stick to GRP repairs!!!

Thats mighty impressive, thanks

Mark

Re: Technical one; possibly for Rohan?

PostPosted: Wed Nov 29, 2006 9:16 pm
by 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

Re: Technical one; possibly for Rohan?

PostPosted: Wed Nov 29, 2006 9:27 pm
by 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

Re: Technical one; possibly for Rohan?

PostPosted: Wed Nov 29, 2006 10:08 pm
by 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 [email protected] 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. :lol:

The 5 speed conversion continues!!!