Lotus Elan

Low numeric 3.x Crown wheel and pinion option

PostPost by: garyeanderson » Wed Jul 18, 2012 11:10 am

There seems to be way too much talk of 5 and 6 speed gearboxes that can be "substituted" for the excellent shifting stock 4 speed that has it's gears spaced well whether its a 2.97 semi-close or the Ultra-close 2.51 ratio version, there is even the poorly spaced Cortina box that has the 3.54 first with a well placed 2.39 second and the cliff dropping third of 1.41 to:1 to be had. What I am getting at is a custom cut 3.1 to 3.25 ratio for the ring and pinion to get something like a 10% reduction over the 3.55/3.54 that is th best highway gear offered now. There are quite a few 1700cc engines that would pull smartly with this kind of gear reduction, it may not be well suited to the lardy plus 2, but for a Elan 1600 to Sprint with the bigger displacement, it would solve a lot of bullshit of the installation of another box and all of the associated nonsense of a gearbox swap and make a quite simple R & P change that would only require a driven speedometer gear change to compensate for the change. I have mentioned this before and it got no responce and I would think that today it will recieve about the same reaction. I see the bigest problem is finding 10 to 20 folks that would like to go this route and put up the money to get it done. My guess is less than $500 would get a Low numeric R & P in your hand verse the cost of the 5/6 speed box. I think I am missing something but not sure of what the resitance of this approach is. Yes it's a slow mornning on elan.net and its already in the mid 80's here so I guess its time to go and sand some putty I spread just before I started to write this question.

Gary
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PostPost by: bigvalvehead » Wed Jul 18, 2012 12:05 pm

Hi Gary
The siearra diff is readily available with ratios of 3.14 and 3.38 some available with LSD.

A bit of work to fit but bombproof and cheap in the UK.

No reason why a good torquey 1700 could not pull that gear.

Another option is the 14 inch wheels that if the suspension is lowered stops the car looking like an off roader but increases the cruising speed at lower revs.

The 6 speed Honda S2000 box would also work with an adaptor plate and they are available for around ?300 in the UK.

Cheers
Dave
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PostPost by: garyeanderson » Wed Jul 18, 2012 12:26 pm

Hi Dave

All good ideas but this mod is a "non-mod" in that it is invisible and totally reversible. No cutting, welding or any other changes needed other than the R and R of Cw&P or if you have a spare center section than make the changes to the spare and your done with the swap in the time it takes to swap out a set of bad donuts. I don't think many 1700 engines need "bullet proof" they only need to handle 135 lb/ft of torque which the stock unit does alright with. big diameter wheels with big diameter ti(y)res need big flairs to fit, some don't want to do the mods to the bodywork to hold a 25 inch diameter ti(y)re. I have a 3.9 fitted to the chassis that is intended for the large flairs that are installed on Tingles C prod body, they are not for everyone and most would not be seen with them. Living with an Elan is a compromise, you can't have it all without sacrificing something else. the custom CW&P seems to involve the least sacrifice but only if 10 to 20 folks think the same.

Gary
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PostPost by: Ross Robbins » Wed Jul 18, 2012 4:33 pm

I have ordered and received a 3.54 R&P from Burton Power in the UK but have not yet fitted it. I am intrigued by the Sierra 3.28 as a ratio that would move the revs down about 16% from the 3.9 ratio as opposed to the 10% from the 3.54. In the lower gears this wouldn't be a problem in most cases though the use of first on a hill at altitude as I did Sunday at 14,000 feet would be tough. For most situations though the reduction in revs would make the Elan more comfortable at speed in the big spaces we have over here in the USA while keeping the sweet gearchange of the original four speed. And, As Gary says, it is completely reversible!! .
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PostPost by: msd1107 » Wed Jul 18, 2012 6:18 pm

elan-f15/updated-spreadsheets-t18445.html has a down loadable spreadsheet. One of the sheets has a variety of r&p combinations ranging from 11/31 2.818, 11/32 2.909, ... up through 9/31 3.444 and so on. 3.444 was homologated by Lotus, although it does not appear to have made it into production.

The Elan R&P uses a pinion with 9 teeth, rather small for a low ratio (3.444 is the lowest done with that pinion). It would be necessary to find an 11 tooth pinion that could be swapped into the Lotus differential.

Then match that with the 37 tooth ring gear from the 4.1 differential to get 3.364. Other possibilities exist.

To stay with the 9 tooth pinion gear, you would need a new ring gear cut. 9/30 gives 3.333, 9/29 gives 3.222, etc. The ring gear might be getting rather too small to fit.

A proper gear cutting shop could easily enough cut a new ring gear given an existing one on which to base the new one. As Gary says, given enough orders, this would be affordable.

elan-f15/speed-candidate-conversion-chart-t16331-14.html has another down loadable spreadsheet where you can enter gearbox ratios and various r&p ratios to see various pieces of data.

Gary and I like the 2.51 1st gear of the CR gearbox. Getting a lower R&P than the current 3.55 makes for more and more driveability problems, and the 1.4 3rd gear in the semi-close box become more problematical as the R&P gets higher than 3.55 also. There is no easy solution, as oodles of posts on various 5(6)-speed conversions attest to.

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PostPost by: Tahoe » Fri Jul 20, 2012 4:08 am

On the early Sunbeam Tigers I used to own, they came with 2:88 gears and close ratio transmissions. A switch to a 3:31 rear with the close ratio trans and a 300+ HP @ 7000 RPM motor in a 2500lb car proved to be a very nice combination. Apples and Oranges comparision I know, but an Elan with 1000 lbs less weight and similar gear combo should perform about the same.

Personally I like my first S2 with a 3:90 and close ratio combo very much and given the speeds we can or should I say can't drive at in the US I hope to someday find close ratio gears again to put in my current S2. I don't need a 5 or 6 speed where I live because the 4 speed with 3:90's is more than enogh to get speeding ticket here.
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PostPost by: vernon.taylor » Fri Jul 20, 2012 5:58 am

Salut Gary et al

Should be meeting a Lotus specialist here in France in the next few weeks. Supposedly he fitted a 3.2 to an Elan and that's one of the questions I'd like to ask him. In a brief conversation on the 'phone he said he could find them, and I think he said they were not from a donor Elan. As you know 3.2 was homologated, so maybe they do exist somewhere.

@+

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PostPost by: jk952 » Wed Aug 29, 2012 10:43 pm

Hi Gary,
Don't study the mods site much so a late reply... Although I have 3.54 in both cars I would be interested, I think a good idea. I would also be interested in an alum. casting -used to be avail. but seems no longer. (just for academic wt saving) diff weighs 40 lb!
Not sue which ratio box I have in the ?lan had a few to choose from - all four speed versions, so output ratio same of course.
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PostPost by: Ross Robbins » Thu Aug 30, 2012 6:51 pm

The 3.54 (11/39) ring and pinon has been fitted and I drove the car yesterday for a few miles. It is a bit harder to get off the line clean but not too bad and at cruise it is much more comfortable keeping up with the modern traffic. I am pleased with the ratio as it is and really would be reluctant to go to a taller (lower numerically) ring and pinon. I will report back after I get a thousand miles or so under my belt.

Now I need to change the speedometer drive ratio to give the correct speed indication. :oops:
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PostPost by: elansprint71 » Sat Sep 01, 2012 9:40 pm

Ross Robbins wrote:The 3.54 (11/39) ring and pinon has been fitted and I drove the car yesterday for a few miles. It is a bit harder to get off the line clean but not too bad and at cruise it is much more comfortable keeping up with the modern traffic. I am pleased with the ratio as it is and really would be reluctant to go to a taller (lower numerically) ring and pinon. I will report back after I get a thousand miles or so under my belt.

Now I need to change the speedometer drive ratio to give the correct speed indication. :oops:


Check your speedo with a gps sat/nav first- my 3.55 is just about true speed. If you fit the "correct" gear it may over-read, like they were designed to do; which, imho is daft.
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PostPost by: msd1107 » Sat Sep 01, 2012 10:13 pm

There are two aspects to this: correct odometer reading and correct speedometer reading.

The correct odometer reading depends on tire size, differential ratio, and the gearbox speedometer driven gear.

Once you have the correct odometer driven gear, if the speedometer does not read accurately, have the speedometer calibrated.

There is a down loadable spreadsheet at elan-f15/updated-spreadsheets-t18445.html that allows you to determine the correct gearbox speedometer driven gear. If the best gear is not available, it allows you to calculate the turns per mile gear pair in the speedometer for the gear pair you have that a Smiths repair shop can put in the speedometer before calibrating it.

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