Lotus Elan

Ultra close gear set and 3,55 diff?

PostPost by: Plus2soon » Mon Sep 14, 2015 2:25 pm

Have any one experience using this gear set and 3,55 diff? I have the chance to overcome the ultra close gearbox (1st 2,2:1) and already have the 3,55 diff. My car is the baby Elan DHC with a 1700 Q420 soon in place :shock: . Currently I use the semi close + 3,55 diff and find the combination quit long legged, but with the 1st too short even now with the standard B-cam engine. Any hints or thoughts are apprised.

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PostPost by: msd1107 » Mon Sep 14, 2015 3:33 pm

The 3.55 diff ratio is the highest easily available ratio for the Elan, but it is hardly "long legged" with a FHC easily running to red line in top gear (as I found out while running in convoy with a Porsche and Ferrari coming back from the historic car races at Monterey).

A 2.2 1st is usually only seen in a racing environment. I use the more normal 2.54 close ratio 1st with the 3.55 and find that acceptable. However, many people find it too tall geared in 1st, requiring some clutch slippage to get off from rest and being a bit of a bother in uphill starts.

I believe it was possible to order S2 and S3 SE with the 3.55 and 2.54 combination, and this seemed popular on the continent. The 2.54 1st normally came with the 3.9 diff ratio. When they went to a 3.77 diff ratio, they went to the semi-close sedan ratios.


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PostPost by: Plus2soon » Fri Sep 18, 2015 10:56 am

Thanks David for your info and advice.

I guess I'll go for the ultra close and test the with the 3.55 as a higher final drive are easier to get hands on if 1st end up too long.

Does any one else have an opinion?

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PostPost by: gus » Fri Sep 18, 2015 11:29 am

The purpose of a transmission is to extract the best performance from the car.

I see lots of discussion about how for some reason people want ever taller first gear.

To what end?

It is extremely unlikely that the close or ultra close ratio gearboxes will end up providing better acceleration than the semi close.

In racing[with very high numerical gearing] it makes perfect sense to have a very tall first gear, as you only use it to start once and the rest of the time you have nicely spaced gears.

On the street with startups from a dead stop dozens of times a day, and with taller street gearing in makes little sense.
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PostPost by: rgh0 » Fri Sep 18, 2015 12:11 pm

It is really about timing and feel for acceleration before you need to select second gear versus hill starts.

In an Elan if you have too low a first gear ratio and diff ratio and tyre diameter combination and you hit the red line in first without barely touching the throttle. You will end up doing second gear starts to avoid a wasted gear ratio

Too high first gear and diff ratio and large tyre diameter and with a passenger and full boot you will find hill starts a pain.

Close ratio box, 3.55 diff and standard tyre diameter works OK in an Elan as long as you have a well tuned engine without a stumble of idle. IMHO. In a Plus 2 it is a little to much if you live in a hilly environment.

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PostPost by: Craven » Fri Sep 18, 2015 4:12 pm

Some numbers worked out years ago so please don?t take them as absolute but give an idea of a close ratio box ( 2.54 ) against 2000E type ratios
With 155 x 13 Tyres. 3.55 Diff. Road speed at 6500 rpm.
----------Semi Close--------------------Close.
1st -------40.4---------------------------47.9

MPH/1000 rpm.
When Mike Spence advertised 130 bhp & 130 mph for the BRM spec it was at 7000 rpm.
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PostPost by: prezoom » Sun Sep 20, 2015 4:49 am

The gear combination cannot be really bad/difficult. My other lump, Ford 204E 1703cc engine, a ZF gear box with the same close ratios, i.e. 2.51 first gear, runs on 165-15 wheels and tires, and an 1800 pound dry weight. Much larger in circumference than the 13's found on the Elans. However, a rather heavy flywheel really helps, it will easily handle most any start situations I have encountered. Even with two people on board. Today's outing to the Vintage Races at Coronado was a classic example.
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