Lotus Elan

An evaluation of 5 speeds for the Elan

PostPost by: msd1107 » Fri Nov 17, 2006 1:20 am

A previous post (http://lotuselan.net/forums/viewtopic.php?t=13892) dealt with the question of what differential ratio an Elan would need to achieve maximum speed. Somewhere between 2.89 and 3.37 was the answer, with the conclusion that any four-speed transmission used would be geared too high in 1st gear, so a five or six speed transmission would be necessary.

Which bring up the question, if we had our druthers, just what ratios would be desirable in a five-speed gearbox for an Elan? Gearbox ratio design, just like virtually every thing else in a car, is fraught with a series of often times conflicting requirements. First gear needs to be low enough to start the car up the steepest slope with the heaviest load. Top gear should allow the car to reach its natural top speed, or be an overdrive ratio for enhanced fuel economy and reduced emissions with top speed reached in the previous gear. The number of ratios should be reduced to minimize cost, weight, and size. The maximum ratio gap needs to be appropriate for the engine power band. An engine with a wide torque band can use a wider ratio gap than can a highly tuned engine.

Let?s look at a couple of concrete examples first, just to get an idea about what it is we are talking. The examples will be the two Elan gearboxes. Assume an Elan with 155-13 tires, 3.77 differential, and 7000RPM.

Close ratio
Main Lay Ratio %diff Speed Diff
21...28
32...17..2.510.............48.7
.....................53.4%.........26.0
27...22..1.636.............74.7
.....................33.0%.........24.6
24...26..1.231.............99.3
.....................23.1%.........22.9
21...28..1.000............122.2
Figure of Merit 99.7 (100 max)
Speed difference increment -1.5mph

Wide ratio
Main Lay Ratio %diff Speed Diff
19...30
32...17..2.972.............41.1
.....................47.9%.........19.7
28...22..2.010.............60.8
.....................43.9%.........26.7
23...26..1.397.............87.4
.....................39.7%.........34.7
19...30..1.000...........122.2
Figure of merit 97.5
Speed difference increment 7.5mph

Interestingly, both these boxes have a 1st to 2nd ratio drop of around 50%, about what a sporting box would have. (Sedans often have more than 65%, racecars and motorcycles can be 40% or less.) So the close ratio box has relatively constant speed differences between gears, while the wide ratio box, with roughly the same percentage ratio drop from 1st to 2nd, have increasing speed differences between gears, with the result that each higher gear feels more widely spaced than the previous one.

Let?s look at some of the more commonly available five-speed gearboxes that have been swapped into the Elan. The first is the Austin Maxi based gearbox as originally fitted on the +2.

The Lotus Austin Maxi 5 speed ratios produce
Ratio %diff Speed Diff
3.200............38.2
........59.2%.........22.6
2.010............60.8
........47.0%.........28.6
1.367............89.4
........36.7%.........32.8
1.000..........122.2
........25.0%.........30.5
0.800..........152.7
Figure of Merit -3.4
Speed difference increment 2.8mph

This is a sedan gearbox, with a wide gap between 1st and 2nd (indeed between all gears, in a relative sense), large positive speed difference increment, and poor Figure of Merit (which should be well above 50). Interestingly, an even higher 5th gear of 0.762 would produce a figure of merit of 97.3, a speed difference increment of 5.1, and 160.3mph at 7,000 (126 at 6,000, 137 at 6,500). So 1st is too low, 5th is too high, and all the ratio gaps are too wide, but remember this is a sedan gearbox. Interestingly, the Lotus factory offered this conversion to me, but I turned it down because I regarded the ratios as inappropriate for an Elan. A good decision 30+ years ago, and still a good decision today.

Another popular gearbox conversion is based on the T9 gearbox. Alan Voight makes probably the best conversion, with good shift feel, proper placement of the gearshift lever, and custom bell housing while retaining the standard sedan box and ratios to minimize costs.


And the MT75 ratios produce
Ratio %diff Speed Diff
3.650............33.5
.........85.6%.......28.6
1.967............62.1
.........43.9%...... 27.3
1.367............89.4
.........36.7%.......32.8
1.000..........122.2
.........22.7%.......27.7
0.815..........149.9
Figure of Merit -11.3
Speed difference increment 0.3

Well, what can we say, this is a sedan gearbox. First gear is virtually unusable in an Elan it is so low, the engine bogs when upshifting and overrevs when downshifting. Although it is relatively meaningless, the ratio progression would be improved with one more tooth on third gear counter shaft, bringing the figure of merit close to 80 and improving the ratio progression as the shift progresses from second to third to fourth.


SPComponents (who make the gearbox for Quaife (http://www.quaifeusa.com) who sell it also) approaches the gearbox conversion differently. The input shaft has the right length and splines to bolt up to the TC engine, although they retain the sedan tail shaft. This means the gear lever is too far back in an Elan, and they offer no way to correct the problem. The Seven and Caterham crowd are the usual users of this conversion. The gear sets offered are more oriented to the competition driver, with the following ratio set being the closest to being useable in an Elan.


And the SPC ratios are
Ratio %diff Speed..Diff
2.390............51.1
........55.1%.........28.2
1.541............79.3
........27.3%.........21.3
1.215...........100.5
........21.0%.........21.6
1.000...........122.2
........14.9%.........18.1
0.871...........140.2
Figure of Merit 39.0
Speed difference increment -3.0

The figure of merit of 39.0 is mediocre, and would be improved to above 95 by adding one tooth to second gear countershaft. Right now, the gearbox feels a little wide between first and second, and a little close between second and third. The change would bring the first-second drop down to under 51% and the second-third drop up to over 31% and the shift progression would feel more natural. In SPC?s defense, they designed the gearbox around a first gear ratio of 2.20 and keep the same third and fourth gears, which makes it difficult to get optimum spacing for other first gear ratios. And this answers the unasked question as to whether a one-tooth difference is even noticeable. The answer is yes, it changes the feel of the gearbox quite noticeably.

Another approach is taken by BGH Geartech Ltd. (http://www.bghgeartech.co.uk/html/5_speed.html). They have cut several custom gear sets while retaining the standard tail shaft and input shaft. They claim the gearbox can be bolted to the TC using a Sierra clutch, and claim to be able to bring the gearshift forward. Probably the most interesting ratio set is their E9.

And the BGH Geartech ratios are
Ratio %diff Speed Diff
2.660...........45.9
......52.0%..........23.9
1.750...........69.8
......38.9%..........27.1
1.260...........96.9
......26.0%..........25.2
1.000..........122.2
......22.0%..........26.8
0.820..........149.0
Figure of Merit 72.9
Speed difference increment 0.7

This is a good set. They offer an alternative first gear of 2.750 which has a better figure of merit of 84.1, but a first-second drop of 57.1%, which some may consider acceptable.

There have been several other five speed transplants, and some other vendors claim to be able to convert other five speeds to fit the Elan. I would appreciate anybody having knowledge and details of other approaches to send them to me so I can incorporate the data. Right now, it looks like the optimum approach might be to use Alan Voight?s tail shaft and shift lever, Quaife?s aluminum case, BGH Geartech?s ratio set, and SPC?s input shaft for a light weight, drop in five speed conversion.

So there it is. The mathematics to perform the analysis are not complex. The spreadsheet to put all this together is not the most simple in the world. There is much more information generated than what was presented here. Anybody curious for more information, querulous about the results presented, or wanting to learn more about this arcane area are welcome to request a copy. An additional plaything in the spreadsheet is the ability to design virtual ratio sets around the Lotus four-speed gear shaft dimensions or the Austin Maxi dimensions with optimum ratio sets of four, five, six, or even seven ratios!

Now, I have been designing gear ratio sets for close to fifty years now, originally using a circular slide rule and lots of paper and not knowing how good the ratios were. I wrote my first computer program around these concepts almost forty years ago, on punch cards and FORTRAN. Now with this interactive spreadsheet, it is amazing how much information and understanding can be acquired in a relatively brief amount of time. It is too bad we cannot get a few people together to cast and machine a near optimal gearbox of five or six speeds that would really complement the near perfection of other aspects of our Elans.

David
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Last edited by msd1107 on Fri Nov 17, 2006 8:17 am, edited 4 times in total.
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PostPost by: alaric » Fri Nov 17, 2006 1:42 am

David, all I can say is WOW! That's got to be one of the longest and carefully thought out posts on the forum.

I converted my elan to a T9 box, partly because it appeared that is was relatively easy to convert the ratios if I decided to at a later date. I would like to work out an optimal set of ratios if possible. If you could send me a copy of the spreadsheet I would be most appreciative. I'd like to compare your approach with how I'd tackle the problem.

This night owl is starting to run out of steam, so it's away to bed....

All the best.

Sean.
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PostPost by: msd1107 » Fri Nov 17, 2006 1:53 am

Hi Sean,

If you would give me an email address I would be glad to send you a copy.

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PostPost by: msd1107 » Fri Nov 17, 2006 1:57 am

Hi Sean,

I forgot to ask, but since you converted your car already, do you know how many teeth are in each gear pair?

That way I could make up a sheet with the possibilities in it already, so you are ready to play games.

David
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PostPost by: Sarah Ryan » Fri Nov 17, 2006 5:12 am

In Australia we had a local car called the Holden Gemini circa 1980-1986. They were either petrol or Deisel & as such two different gear boxs. A lot of Elan owners simply visited the local wreckers purchased either of these box's. They are an Alloy box about 12kg lighter than the Ford box, five speed, unbreakable, reliable & leak free. The gear ratios are the same as the close ratio Ford box except for first that being 3.2-3.4 with fifth being .87. We use an adaptor plate between the bell housing & the block along with a Saab concentric slave cylinder. The only other modification is the prop shaft.
Works a treat with the gear handle in the right position along with fast positive gear change. Suggest all of you relocate to Australia & convert as there still a lot of them sitting in the local wreckers.
Nice reading the article not sure I understood it all.
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PostPost by: worzel » Fri Nov 17, 2006 9:07 am

Just some additional info.

It's possible to alter 1st on the Type 9 from its lowish 3.65 (boxes from 1.6/2.0 Fords) or 3.35 (from 2.8 cars) to 2.97 as per the original 4 speed.

However, what are we actually talking about- is this dragstrip territory for the public roads?

Do people actually drive with these numbers in mind- I've got the 3.35 1st and in all honesty have never really noticed the difference in gearing in give and take situations. Track situations will be different but for road use the light weight of the elan seems to mask gearing differences in the intermediates.

John
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PostPost by: John Larkin » Fri Nov 17, 2006 9:39 am

I have a Voigt conversion in an Elan S3SE for about a year now. I'm happy with the conversion. I acquired a 1973 Sprint in June of this year, and since I have started driving both cars regularly I have noticed that the Sprint has a longer first gear than the S3 with the Voigt box. The difference is not enough to make me want to change the first gear ratio in the present Voigt box, but if I was ordering another I would get a higher first gear.

Anybody interested in David's proposed special gearbox?

How many boxes would be needed to make it financially viable?

Could Alan Voigt make it I wonder?

John Larkin.
1967 S3SE FHC, 1974 Rover P6B, 1949 Lancia Aprilia
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PostPost by: ppnelan » Fri Nov 17, 2006 10:04 am

I personally am happy to accept that Lotus probably knew what they were doing when they deisgned the Elan... :wink:

They naturally used off-the-shelf gear ratios to reduce costs, but I'm sure they didn't compromise OVERALL performance greatly by doing so.

They supplied 4- and 5-speed versions to suit different requirements. These may be a little under-geared if you have to travel long distances, especially on motorways, but if you want modern car cruising capabilities then why not use a....er.....modern car ?! For me, it's all part of that classic car experience...

If you want maximum performance you just have to look at the 26R versions that underwent considerable development to achieve this aim. 6- & 7-speed transmissions are all well & good, but what about those valuable seconds wasted changing gear...?!

Excuse me now, while I remove my wing mirrors, indicators & sidelamps to try to see if I can get to work any quicker today :!: :wink:

Kind regards,
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PostPost by: steveww » Fri Nov 17, 2006 6:51 pm

When the Elan was first designed motorway cruising was not a consideration as there were not any motorways. The high rpm motorway cruising is the only thing I do not like about the Elan. I try to stay away from this type of road but they are still the best way to cover distance even in an Elan. On the plus side the 4 speed box is so sweet and direct in its changes that driving on twisty back roads requiring use of all the gears is a joy 8)

I would like to drive an Elan fitted with a type 9 to see what the shift quality is like. My memories of the old Sierra are not so good. If the shift quality is as sweet with a type 9 I could be tempted to fit one.
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PostPost by: 1964 S1 » Sat Nov 18, 2006 4:41 am

The autobahns and perhaps our interstates preceded the motorways, and the Elan, but it was never designed for any of them, not enough corners. I'm back to that question of how fast would you wanna go in an Elan. I've driven 100+mph in mine and said, ok, now what?

I'm a "ditto kiddo" to Matthew. I too think the Elan is simply brilliant as designed and geared. No one has built a more fun street car for ripping up and down through the gears, the S1 is 44 years old. In first gear I can go 40 to 45 mph, but guess what, while going less than that I can grab second gear and then really be gone, third and fourth exceed posted speed limits. Can I tell the difference in zero to eighty times when one or two seconds are involved? No. What do all these ratios mean? Sure a fifth or sixth gear might be nice in an Elan but name a car, any car, that wouldn't benefit from some .697 taller or lower gearing somewhere in the gearbox or differential.

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PostPost by: msd1107 » Mon Nov 20, 2006 10:25 am

First of all, thanks for all that responded, both in the forum and personally.

A little philosophy. My father was an engineer, and in the ?40s designed and built a complete audio system. So I grew up with an appreciation of music, and not liking distortion. At my last job, we made sound cards and speakers. I educated both marketing and my engineers on good sound, for what to listen and how to measure and design for high fidelity. Sales competed on price, marketing emphasized features, engineering had to design to a feature set at a competitive price. I have installed HDTV and 7.1 sound, and calibrated the video and audio to a rather high standard. To me, it is worth it. But my girlfriend is a technophobe, and cannot see or hear these things. To each their own.

In the ?60s, I had a vehicle that I found out, by studying the parts catalog, had replacement gears that differed by one tooth from stock for many of the gears. I was able to experiment with this, and verified that the feel of the gearbox changed as I changed a gear. Wider ratio, or narrower, it made a difference and validated the theories I had formulated, even though I had not yet reduced the theory to a computer program. So I got to use an optimized gearbox, while the rest of the users got by with the standard ratios.

We all agree that Colin Chapman was a brilliant engineer, and had a team of brilliant engineers working with him. Chapman was also a businessman, determined to make Lotus a success. After the Elite, which was a technological success but a financial failure, Chapman focused on the cost structure of his next car, the Elan, which was to be a ?sports?car, not a thinly disguised racecar. So, as much as possible was bought ready made, so that effort could be expended in areas that brought returns, like the chassis, body, and cylinder head. Other things, like the engine and transmission, were bought from existing sources. If you remember, the first Elans had the 1500cc engine and sedan gearbox, which drew negative reviews in the motoring press. The Cortina rally program saved the transmission day with the 2.51 gearbox, and specially selected blocks allowed for 1558cc displacement.

Chapman was not averse to changes and improvements. When the first modified Elans with 3.9 R&P blew up regularly on the autobahn, Lotus homologated the 3.55 R&P, and then the 3.44 for long distance racers. And people who insisted on racing their supposedly road going Elans eventually got a factory based racer, the 26R, basically a new Elan, but more suited for racing.

Spin forward 40 years. We have a nice touring car using 40-year-old technology. The fact that it was advanced for its time mitigates the fact it is 40+ years old, and virtually every aspect that was advanced in 1962 is probably now technologically obsolescent. It is still enjoyable to drive, but eclipsed in capability by many modern cars. Obviously, given 40 years of technological advancement and the 26R as a guideline, many improvements can be made.

So, starting at the front, the inexpensive steel wheels can be replaced with light weight forged aluminum wheels (or even the Lotus magnesium ones), the cast iron hubs replaced with aluminum ones, the cast iron calipers replaced with aluminum ones, the Spitfire suspension with tubular, the heavy copper radiator replaced with aluminum, the unreliable and power robbing water pump replaced with an electric one, the cast iron bellhousing replaced with aluminum or magnesium, the flexible chassis replaced with a reinforced TT replica or a Spyder one, etc, etc. None of these were available or affordable for the production Elan back then, but Chapman would approve of each and every one of these, since they conform to the Lotus mantra of adding lightness or utilizing advanced technology for improved performance. And they all, incrementally, make for a better Elan experience, provided you can afford it and have the time to make the changes.

The same applies to the transmission. The technology in 1962 did not support the design of optimized ratio sets. Believe me, I generated stacks of paper with ratio designs that, at the time, I believed were good, but now realize were not optimum. I presented the concept to Lotus to optimize the gear selection for their F1 cars, but, even though it was interesting, the industry at that time was not capable of utilizing it. Of course, now every F1 team utilizes a somewhat equivalent modeling technique as you can tell by watching speed Channel.

It is true, as many of you have pointed out, that we can live with our four speeds, whether wide ratio or close ratio. And several have pointed out that they did not realize the limitations with which they were putting up, especially those with five speed conversions. Having a car for 40 years is like being married; you get used to the foibles and limitations without thinking of how things can be improved. But a car is not a marriage, and if we know how to improve it, we can, and should, try. I do not think your wife would agree to the opposite proposition.

Personally, I am retired, and am not seeking to benefit financially from this. (Being on an ANSI Standards committee is a good example of devoting oodles of time and effort for no compensation with the only satisfaction being knowing that you advanced the common cause). I am willing to provide personal services, travel support, and the software to support the development of a gearbox for our Elan community, and pay my fair share of the gearbox cost. Remember, the technology in the software is unique to our group, we are in an industry leading position here. Let us find a supportive organization that can put together the pieces needed ? aluminum case, shift linkage, gear cutting, compatible input shaft and output shaft ? for an admittedly small production effort. The production volume of the Elan, in round figures, was 10,000. Maybe 5,000 exist. And, optimistically, 1% of those may be interested in a new gearbox. That is 50 units! Not many businesses are interested in something this small, at an R&D cost that is affordable amortized over only 50 units. But that shouldn?t keep us from trying, since the technology can be adapted across other transmissions, which would minimize its eventual cost.

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PostPost by: garyeanderson » Mon Nov 20, 2006 1:01 pm

Hi David
I don't really see the need for the 5 speed box on a car as light weight as the Elan. Some of the best recorded timkes "0 to 60 mph",1/4 mile, and top speeds were in late Coupes with 3.55 ring and pinnion. If you were to fit some 185/60x13 or 185/60x14 tires (with appropreate flairs) and use a redline of 7100 theoretical top speeds climb to near 130 mph and 135 mph for the 2 tire sizes mentioned. The biggest limitation then becomes driving in town at 5 to 15 mph range with the 2.51 first gear that is good to over 50 mph.
Both options are available today, it all comes down to money and time to make the Elan what we want it to be.

Gary
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PostPost by: msd1107 » Mon Nov 20, 2006 5:01 pm

Hi Gary,

Yes, you are entirely correct. The fastest road test speed was achieved in a FHC with 3.55 and 155-13 tires, but with the wide ratio transmission.

I have personally run the 3.55, 2.51 combination for years, first with 165-13, then 185/70-13 when high performance 165s were not available (practically the same tire rev/mile), and now 185/60-13. I wonder how many people want to deal with that combination starting up a hill with a passenger. I know my girlfriend wondered why I got tense when I would take her to work and have to stop at a traffic light up hill. That is, until she got to drive the car!.

But if the engine is modified highly enough for a power peak of 7,000, then you are going to want gearing for more than 130. As a quicky, taking the cr trans as a basis, theoretical ratios of 2.5, 1.67, 1.25, 1.0, and .83 would make a good starting point, and would work well with 185/60-13 and a 3.77. Or 185/60-14 Minilites with a 3.9. That is why I use my spreadsheet, because it allows me to model possible changes quickly. And it already has corrections for the real tire rev/mile versus what is calculated from the tire dimensions (i.e. for 185/60-13, the theoretical rev/mile is 928, but in reality it is around 956)

All of these considerations are very complex issues, as is usual with things car related. I know you have a very light car, so you can get away with gearing that some one in a S4 with a passenger and luggage couldn't.

David
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PostPost by: garyeanderson » Tue Nov 21, 2006 12:20 am

Add displacment for the street, 1700cc is a relatively easy. Loose the extra weight off the front first, start with the headlamps and vacuum canisters, go with a fixed 26r type of system, stock seats are heavy and so on. My S2 launches best with a passenger.

Gary
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PostPost by: ppnelan » Tue Nov 21, 2006 7:41 pm

Just wondering how much lighter is an ALUMINIUM wheel over the standard steel wheel:?: They are pretty light by wheel standards, which is why they crack when pushed hard, typically on modern tyres.

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