Lotus Elan

diff ratio?

PostPost by: Elanconvert » Tue Feb 11, 2014 6:17 pm

maybe for you, bill!! knowing me, I'd lose count and keep having to start over :lol:
what happens if one is hidden behind a lorry?
how accurate were they put in in the first place?
also, is it not illegal to drive with one finger on a stopwatch?!!!

think I'll stick with GPS......... :D
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1970 S4 dhc big valve
1973 Ginetta G15
1967 Ginetta G4 [sadly now sold]
1959 lotus elite type 14
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PostPost by: billwill » Wed Feb 12, 2014 12:13 pm

Take a passenger to do the counting & stopwatch.

They have numbers like 17.3 , so you can correct if you miss seeing one.

Anyway there's plenty more on any typical motorway trip.

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PostPost by: bill308 » Mon Feb 17, 2014 7:50 pm

My S2 SE 26/5327 had a 3.55:1 when I bought it used over 30 years ago. My parts book shows part number 026 R 0703A for the 3.55:1 crown wheel and pinion, clearly a pre S3 part number. The 3.9:1 also shows as a pre S3 part, the 3.77:1 does not.

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PostPost by: Chancer » Tue Feb 18, 2014 12:34 am

Interesting to learn of the early vehicles being fitted with a 3.54 diff ratio, was it specially made for Lotus as I cant think of any Ford production vehicles of the time that could have handled such tall gearing, maybe something with little wheels :lol:

Corsair V4 perhaps?
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PostPost by: rgh0 » Tue Feb 18, 2014 3:44 am

The 3.55 ratio was Lotus specific as far as I am aware. Ford brought out a 3.54 diff later with a different tooth count.

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PostPost by: Quart Meg Miles » Tue Feb 18, 2014 11:12 am

The Workshop Manual October 1972 describes the 3.9 as being 43:9 (which should, of course, read 43:11). Mine is actually 39:10 so was 43:11 ever produced, it is just 0.23% different in ratio?

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PostPost by: msd1107 » Tue Feb 18, 2014 8:56 pm

The 3.556 differential ratio was 9:32. Lotus "homologated" a 3.44 differential ratio 9:31, but it does not seem to have made an appearance.

A 11:43 would be 3.91, close to the regular 3.9 ratio. You might look at the Sierra differential gears to see if such a combination is available, or could be put together.

The larger gears in the 11:43 might offer slightly less friction losses than the smaller 10:39, but probably not enough to be noticeable. If you are interested in friction reduction, have the ring and pinion REM treated, which is now widely available and not too costly. For even greater friction reduction, RF85 is available, but is quite a bit pricier.

The 3.55 ratio (9:32) was introduced fairly early on, probably in reaction to drivers taking out the rev limiter and driving their cars at 7500+ on the Autobahn. Even with the 3.55 ratio, the FHC would still get to 7000. The later 3.54 was 11:39.

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