Lotus Elan


PostPost by: leifanten » Sun Jan 17, 2010 5:15 pm

Nice engineering and craftsmanship!! Kudos to yo mate.

Is the holden a rear wheel drive? In Europe there is a front wheel drive vauxhall/ opel ascona C that looks just like the first picture you posted.
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PostPost by: memini55 » Sun Jan 17, 2010 7:23 pm

Kiwi Elan,
What a wonderfull aporach to a five speed installation! There are a couple of us in the US who have been trying to make contact with Ray Edwards and others who have done this conversion, but I must say your job seems to be the best and most well thought out of any I have seen. I will study the post closely and I am sure we will ask questions as we get things moving along. I have two gearboxes in the waiting.

Thanks again and best regards
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PostPost by: jabingb » Sun Jan 17, 2010 8:23 pm

I echo Mark's and the rest of the comments, WELL DONE! I work in a CNC shop and would very much appreciate a copy of the "adapter plate" program if possible, at least a DXF drawing? I will understand if you wish to charge a fee for this as I can appreciate the development effort expended.
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PostPost by: stugilmour » Sun Jan 17, 2010 8:36 pm

Excellent job Kiwi Elan.

Today I was rummaging through some of the old posts on the various five speed topic(s), and I noticed David (AKA msd1107 in Hollywood CA) posted some info from the factory service manuasls on various Isuzu transmissions that were presumably sold into the US market. His original post with an attached spreadsheet is here:


Although David cautions the data in some sections of his listings may need review, the MUA 5-Speed transmission he lists with the same gear ratio's as the Kiwi Elan ones appear to be installed in the following Isuzu models:

19?? to 19?? Amigo with the ZE1 V6, 3.0L
1988 to 1994 Pick-up with the 4ZE1 I4, 2.6L
1990 to 2004 Rodeo with the 4ZE1 I4, 2.6L

Not sure how these relate to the various versions Kiwi Elan highlighted in his excellent report, but might provide a good starting point for folks trying to source the correct box.

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PostPost by: johnc » Sun Jan 17, 2010 10:22 pm


I believe Marcine's transmission is of the MGA series, not the MUA series. Referring to Maurices' photo #5, note the shifter mount slants downward. My understanding MUA series shifter mount is horizontal, whereas the MGA series slopes downward.

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PostPost by: alexblack13 » Sun Jan 17, 2010 10:47 pm

Hi Maurice
I would like to add my congrats! If I were doing a 5 speed conversion this would be a serious contender for me also and I would have no hesitation in purchasing the drawing & details how to go about this job. I suggest you get on with marketing this.

I would have the plates made and supply them with a set of instructions / pictures etc. You will have many takers I am sure.

Well done!!

Alex B.... 8)
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PostPost by: johnc » Sun Jan 17, 2010 11:12 pm

Nuts. In my previous post my reference to MGA series should have been MSG series. In other words, I believe Maurice's transmission belongs to the Isuzu MSG series.

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PostPost by: dusty » Sun Jan 17, 2010 11:21 pm

Superb write up and engineering, glad it worked out so well.
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PostPost by: stugilmour » Sun Jan 17, 2010 11:24 pm

Thanks for the correction JohnC, MSG it is. :oops: David's sheet has a similar descriptor in remark 5, but I missed it. The ratio's he lists are different from Kiwi Elan's though, although he did say he was uncertain of them in the sheet. Not sure what the candidate donor car in NA would be with the correct ratio's? I thought the ratio's quoted By Kiwi Elan looked pretty good, but I am a long way from expert on that topic.
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PostPost by: CBUEB1771 » Mon Jan 18, 2010 1:25 am

As with all the others. I can only say thanks many times over for your effort. It will take a bit of time for me to absorb everything you have done. Great job!
Last edited by CBUEB1771 on Mon Jan 18, 2010 2:21 pm, edited 2 times in total.
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PostPost by: garyeanderson » Mon Jan 18, 2010 8:42 am

Howdy Maurice

Finnally someone has figured out what a great way this Forum offers to present an Idea from start to finish. I have nothing but the highest respect for you, your determination, and your willingness to share with others. There has been so much talk about 5 speed boxes in an Elan/Plus2 that it has lost its way. It takes someone with the get up and go attitude that you have shown us to get the others of us (those of us that sit in front of this screen for to many hours each day) waiting for someone to do it. Its not the box I want but I am sure that there are plenty of people out there that would love to have a 5 speed, ANY 5 Speed. A gearbox with both an underdrive and an overdrive will be just fine for most people. Some of us will not give up an ultra close box for anything but the same plus 1. I don't know which cars or trucks the box came in but I suspect that this is the same box that was delivered in the Isuzu I-MARK, Opel Cadet, Chevy Chevette and a host of others. Maybe the early Isuzu Impulse Turbo before they switched to FWD.

http://www.drivetrain.com/parts_catalog ... u_car.html

4cyl 1.8L MSG-5T 1981-85 5spd, RWD alum. case, rear load See Detailed List

4 cyl 1.9L MSG-5T 1983-86 5spd, RWD alum. case, rear load See Detailed List
4 cyl 2.0L MSG-5T 1983-87 5spd, RWD alum. case, rear load, TURBO and non -TURBO See Detailed List
4 cyl 2.0L MSG-5T 1987-89 5spd, RWD, alum. case, rear load, TURBO only See Detailed List
4 cyl 2.3L MSG-5T 1987-89 5spd, RWD, alum. case, rear load, TURBO only See Detailed List

Many links on Lotuselan.net also

http://www.google.com/search?hl=en&q=+s ... CDYQrQIwCQ

I haven't looked at this but it probably explains all of GM's itterations of this doner, 25 models with the same name.

A most unlikely candidate is the Chevy Chevette Diesel/Pontiac T1000 ( I think this had the diesel options also) 5 speed.

As for producing your adapter plate, I think you need to figure a price for a finished piece and let others know what it is. The next step is to see who steps up to the plate and sends money. Otherwise this 5 speed debate/thing may continue for decades...
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PostPost by: frearther » Mon Jan 18, 2010 12:34 pm

Damn fine work! I'm envious.
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PostPost by: John Larkin » Mon Jan 18, 2010 10:48 pm

Well done Maurice! Very impressive work.

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PostPost by: msd1107 » Tue Jan 19, 2010 2:59 am

A previous post elan-f14/twin-cam-bellhousing-anyone-t15954-120.html had a comparison of the various ratios available for the MX-5 gearbox, plus the Lotus 4-speeds, many of the ratios available for the T9 gearbox, and the most suitable ratios for the T5. I had forgotten about the Isuzu, but Maurice?s post outlines the advantages of this gearbox. Since it is raining (in SoCA?) I decided to extract the same technical data for Isuzu gearboxes and splice in some of the other gearboxes for comparison.

For each gearbox, the information extracted is as follows: "Gb ratio" is the gearbox ratio, in 1st through top from top to bottom. "% diff" is the percentage difference between the current gear and the next gear. "speed" is the speed achieved at 6,500 rpm. "diff" is the difference in speeds achieved in the current gear and the next higher gear. "err" is the error term for this gear and the next gear when the program calculates the Figure of Merit (FoM). Zero is best, low single digit figures OK, larger figures not OK. The math is simple, the results illuminating. "FoM" is the Figure of Merit. This is a mathematical calculation as to how well the gear ratios are staged. The maximum is 100, and there theoretically is no minimum. You will perceive a gearbox with a FoM above 80 as being a well-staged set of gears. By the time the FoM gets down to 0, there will be awkward gaps between one of more ratios and either too wide or too narrow a gap.

Now, let?s take a pretend drive in 9 cars with 9 different gearboxes. Back-to-back drives allow for the evaluation of subtle differences between gearboxes that appear to be close together and that might not be so noticeable individually. But the wide range of gearboxes makes differences quite noticeable. I will proceed from the highest geared 1st speed to the lowest geared 1st speed. All the data assumes a car with 155-13 tires, 3.55 differential ratio, and 6,500 rpm. If you want to see results for other configurations, download the spreadsheet (20080411z.xls) at the bottom of the first page of posts at viewtopic.php?t=16413&view=next .

Lotus CR 2.51 1st, 4th direct.

Gb ratio % diff speed...diff...err....FoM=99.8
2.510....53.4...047.9...25.6...00.0...51.9 at 7,000

On startup, the acceleration feels soft due to the high gearing (50+ if you go to 7000). 1st to 2nd feels medium close, basically because the gearing is high (in many cars, this is similar to 2nd). 2nd to 3rd feels a little closer, and 3rd to 4th feels closer still. Looking at the speed difference between gears shows why. The speed difference decreases for each gear, giving the impression of closer gearing. Notice the FoM of 99.8, as close to perfect as you are likely to see.

BGH E7 2.66 1st, 0.82 5th

Gb ratio % diff speed...diff...err..FoM=72.8

The BGH E7 looks quite similar to Bill?s proposed set in 1st through 5th (see link above). The differences are primarily in 2nd and 3rd, and although appearing minor, result in a decrease in the FoM from 90+ to 70+. If you drove these two gearboxes back to back, you would be able to sense the differences as you shifted up through 1st through 4th.

Lotus ?Mid-close? ratio 2.97 1st, 4th direct.

Gb ratio % diff speed...diff...err..FoM=97.5

The so-called ?mid-close? ratio is actually a sedan ratio set. Startup is much easier in 1st since the Elan is quite a bit lighter than the corresponding sedan. 1st to 2nd feels closer than the Lotus CR and Bills hypothetical 6-speed gear sets. It is in an absolute sense (% drop of 47.9% vs 56.9% and 53.4%) but the speeds are lower, so the mph difference is less also (19.5 mph vs 25.8 and 25.6). 2nd to 3rd feels a little wider (26.3 mph difference vs 24.6 and 24.2). The 3rd to 4th shift feels quite wide, both percentage wise (39.7% vs 26.5% and 23.1%) and speed difference (34.2 mph vs 25.2 and 22.6). The FoM is an excellent 97.5, which shows that you can generate a set of ratios that measures well, but does not drive so well.

Isuzu Gemini Twincam 3.174 1st, .855 5th,

Gb ratio % diff speed...diff...err..FoM=-406.6

The 3.174 1st gear is lower than desirable but will work acceptably with the 3.55 differential. The first four ratios are spaced well, with an increasing mph differential between gears. Indeed, ignoring 5th gear produces a FoM of 93.6. In this case, the gearbox designer may have wanted a close gap from 4th to 5th. Using the Isuzu Piazza Turbo 5th gear ratio of 0.775 improves the FoM to 94.8, so that if the gears can be swapped, this is the way to go.

T9 2.8 3.35 1st, .82 5th,

Gb ratio % diff speed...diff...err..FoM=-257.8

A big problem is in the very wide 85.1% drop between 1st and 2nd and the smaller speed gap between 3rd and 4th . See this in the %diff column and speed diff column. The large figures in the FoM err column also accurately predict problems with these ratios and lead to the ?257.8 FoM.

Isuzu Piazza Turbo 3.431 1st, .775 5th,

Gb ratio % diff speed...diff...err..FoM=80.6

The 3.431 1st gear is lower than desirable and the 1st to 2nd gear drop is much larger than desirable. The top four ratios are spaced well, with an increasing mph differential between gears. Indeed, ignoring 1st gear produces a FoM of 92.2. In this case, the gearbox designer may have wanted a lower 1st gear for startup ease. Using the Isuzu Gemini Twincam 1st gear ratio of 3.174 improves the FoM to 94.8, so that if the gears can be swapped, this is the way to go.

Isuzu diesel 5-speed 3.48 1st, 0.86 5th,

Gb ratio % diff speed...diff...err..FoM=-360.5

The diesel gearbox has been mentioned before. The difference between the diesel ratios and the Piazza Turbo is fairly small, and the FoM of the 1st 4 ratios only is 93.2. Using the Piazza 5th gear ratio of 0.775 would bring the FoM up to 97.0. The 3.48 1st gear is lower than desirable and the 1st to 2nd gear drop is much larger than desirable. So none of the Isuzu ratios sets is desirable, if you could mix and match the best 1st or 5th gears, the whole gearbox would be close to ideal. This gearbox is lighter than a T9 or T5 gearbox, and the cost of conversion is probably less that an equivalent T9.

T9 1.6 3.65 1st, .815 5th,

Gb ratio % diff speed...diff...err..FoM=-11.3

The 3.65 1st gear is almost the same as the S15 3.626 and noticeably higher than the MX5 1st gear. However, there is a large ratio drop between 1st and 2nd, a small speed gap between 2nd and 3rd, and a large speed gap between 3rd and 4th. This is seen in the speed diff column and the FoM error column.

Maurice?s Isuzu 3.77 1st, .81 5th,

Gb ratio % diff speed...diff...err..FoM=-507.3

The 3.77 1st gear again is really just a startup gear. The 1st to 2nd shift is reasonable at 63.2%. The rest is pretty much a muddle. The 2nd to 3rd shift at 65.0% is greater than the 1st to 2nd shift, which makes the shift feel wider than the 1st to 2nd shift. The MPH drops between 2nd and 3rd and between 3rd and 4th are much greater than the drops between 1st and 2nd and 4th to 5th. The FoM of ?507.3 reflects the difficulty in matching a reasonable shift progression with the actual gear ratios. You can see this in the err column where each shift has a substantial error compared with better staged ratios. Actually, if we exclude 1st gear (which would be normal operating procedure in real life) the FoM increases to 32.7. Sometimes on these wide ratio sedan based gearboxes, I find the top 4 ratios to be rather reasonably staged.

For those who are doubtful as to being able to detect these differences, you only need to do a back-to-back once to be convinced.

So what is a person to do? As usual, there is no perfect solution. If you can cope with 1st gear startup and do not do long distances on the freeway, then the Lotus CR is as good as you are likely to get, and it is completely standard. The Esposito/Voight/BGH E7/Quaife 5-speed is a possible candidate, provided John can get production quantities and assuming you can stand the price. Although John is in the US, the gearbox can be delivered worldwide. For a DIY ?solution? in the US, a T5 1352-184 1988 Sierra 2L Turbo 2.95 1st, .80 5th would work well, although you suffer a considerable weight penalty and can?t use a Spyder chassis. If you can mix and match the appropriate 1st or 5th gears with the corresponding Isuzu Twincam, Piazza Turbo, or diesel you would wind up with near ideal ratios and a gearbox that is lighter than the other candidates. A properly engineered conversion like Maurice?s at a reasonable price would be a real winner. As usual, your particular situation will determine what solution you choose.

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PostPost by: tinker » Tue Jan 19, 2010 1:09 pm

Maurice, Well done, what a nice neat conversion and an excellent write up. Also nice to hear your well pleased with the final result. No doubt mr Chapman himself would have gone down a similar route if he could have found a suitable box cheap enough. Tony.
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