Lotus Elan and Lotus Elan Plus 2 Forums

Picking up on the encouragement of David aka msd1107, I reorganized and expanded the transmission chart I posted in the Elan - Isuzu 5-speed thread.

The chart contains sections for Isuzu, T9, T5, and Alfa Romeo transmissions -- all of which were reported to have been adapted for Elan usage in one form or other.

Any corrections and / or additions are welcome.

Thanks John,

Good spreadsheet!

No wonder my +2 5 speed is so slow off the line.....

And here's me thinking my 100kg was holding it back

Take care,
Peter

There are a half a dozen folks that I have talked with that would not give up the ford base ultra close ratio gearbox for anything. That said what people seem to want is a box that can give them 70 mph at 2500 - 3000 rpm. With the tire scituation in the U.S. it is looking more and more that a set of 13 inch tires will soon eat most of a $1000. I am starting to think that a larger diameter will be the only available option. So I am going to make some room in one of my S2 shells to fit them, along with the 3.55 ring and pinion. there will be some clutch slipping to deal with and a change in driving style though 20 mph school zones but I think it is something that I can live with. If I thought I could keep getting 13 inch tires I would get the custom cut Ring and pinion in the 3.1x to 3.2x that I have talked about in the past. This is a cheap (dollar wise) solutution. I really cant see any of these 5 speed conversions costing less that $2000 U.S.D. to get it installed into an Elan. This is not the kind of box that I have at the present, to get the equivalent ratios will be north of $3K and probably closer to or over $4000.

David and John
The xls chart needs something about rear end ratios and tire diameters to make it meaningful.

garyanderson wrote:

The xls chart needs something about rear end ratios and tire diameters to make it meaningful.

If you mean adding calculation capability, I find the XLS program at http://westfield-world.com/gearboxshifts.html helpful. Click on "Gear Ratio Calculator" which will load the program into Excel. After it is loaded, if you want a local copy of the program click on "save as".

If you are thinking of something else -- let me know and I add it.

johnc,

The Westfield calculator has inaccuracies. I wrote them last year.

As Gary requested, I added a sheet to your spreadsheet that could cover what he wants. Really a quick and dirty cut and paste with no user instructions.

Hope this helps.

David
1968 36-7988

Since the owners manual for my wife's toy is sitting right here, I can help on the Alfa end.

For a 1972 Alfa 5 speed the ratios are:
1st 3.30
2nd 1.99
3rd 1.35
4th 1.00
5th 0.79
Rev 3.01

Of course the shift throws are pretty long even if you put a short stick on it like you would need for an Elan, and I haven't been particularly impressed with the synchros on any of the family Alfa (father-in-law has 2). Ours is worse then most though.

Rob

Hi Rob, this should be a safe place to rip Italian synchros. Can you even imagine what an Alfa trans would do after the third red line shift in an Elan?
Eric

Hey guys, you are downloading too quickly!

Enclosed is an updated spreadsheet from johnc.

Various formatting changes.

Updated the BGH T9 to .82 5th since this produces better ratios in a theoretical sense. Racers can select closer ratios if desired.

Added the 2.75 1st gear set. Mike Ostrov, when he did the T9 conversion for the Elite, chose the 2.75/.82 ratios. If you have ever driven this car, you would agree it is a very nice set. Gary and I would still hold out for a 2.5 1st gear, though.

Added Alfa-Romeo ratio data from my 60s era SCCA specification data book. Don't even ask why I still have this. It still has all my original notes on gear ratios, drops, optimum selections, etc.

Added Toyota gearbox data for a variety of their rear wheel drive gear boxes.

Added user instructions for the sheet that displays speed vs differential ratio and gear ratio. There are four aspects to this, tire rev/mile, RPM, differential ratio, and gearbox ratio. There are 6 ways to display this information in 2-dimensioal tables. You are getting one, I have a spreadsheet with the others, in case anybody is curious.

David
1968 36/7988

I expect to have the engine out of my +2 in the fall and would like to take the opportunity to install a 5 speed. In the US some highway travel ( hours at 75 mph) is largely unavoidable. Besides the T9 conversion any other suggestions for a road car with 1700 cc and a mild sprint cam?
Phil in Tennessee

PWTrusty wrote:I expect to have the engine out of my +2 in the fall and would like to take the opportunity to install a 5 speed. In the US some highway travel ( hours at 75 mph) is largely unavoidable. Besides the T9 conversion any other suggestions for a road car with 1700 cc and a mild sprint cam?
Phil in Tennessee

I've used the MT75 from the 'sulking frog' Scorpio, the box needs some modification to fit within the chassis rails and the output flange (transit) needs reducing in diameter. The shift is superb, better than a four speed original but its a real pain to fit, fouling the chassis at the top and the exhaust at the bottom, also the starter position is is rotated down wards and fouls the sump. I have used a TC Europa (austin Maxi) pre engaged starter and that fouls the chassis slightly.

After all of this effort the car still isn't finished so I can't comment on how the conversion has worked, I do know that 1st is very short but 5th(most real world driving is done in 3rd to 5th, 1st and 2nd for pulling away/around town. I intend to use my car for everything..trips to town, b road blats and long runs on motorways, so I think the benifits will out weigh the short comings. Worse case scenario the four speed can go back in!

If you want some pics of the install i can email them to you.

regards

Mark

Update for the 5-speed candidate conversion spreadsheet.

Updated Elan ratios using actual tooth counts. Included 3rd party gearsets.

Improved formatting for Toyota section.

Added a section for Datsun transmissions. There are sure a lot.

Should we include any other manufacturers or transmissions?

David
1968 36/7988

Attached is the list of MT75 ratios at least for Scorpio Applications

Gerry

Updated spreadsheet including Gerry's MT75 ratios.

I took Gary's comments about not giving up the close ratio transmission to heart, as I feel the same way. When my first Elan was consumed by fire, I bought back the pile of pieces to retrieve the CR box.

Interestingly, the general set of ratios in that box has been used through the years and across many manufacturers. It may be close to the "perfect" 4-speed ratio set.

There are some interesting mathematical properties in the ratios. The 1st to 2nd ratio spread is 50% (in round terms) which seems to be a good compromise, not too wide, not too close. Numerologically, it is a 3/2 ratio.

The speed gaps between ratios are relatively constant, which seems to produce a good feeling staging of ratios. So, if it gets 100 mph in top, the speeds in gear are 40, 60, 80, and 100 for a constant 20 mph gap.

Again bringing forth numerology, the gearbox ratios can be generated with a number sequence. In this case, the sequence 5/2, 5/3, 5/4, and 5/5 generates the ratios 2.50, 1.67, 1.25, and 1.00.

This can be extended to produce 5 ratios, 5/2, 5/3, 5/4, 5/5, and 5/6 for 2.50, 1.67, 1.25, 1.00, and .83 for an overdrive 5th. Or 6/2, 6/3, 6/4, 6/5, and 6/6 for 3.00, 2.00, 1.50, 1.20, and 1.00 for direct top.

The corresponding 6-speed would be 6/2, 6/3, 6/4, 6/5, 6/6, and 6/7 for 3.00, 2.00, 1.50, 1.20, 1.00, and .86.

Looking at the canditate 5-speeds in the spreadsheet produces a sinking feeling in me. First gear ratios of 3.3, 3.5 or lower just don't work well in our light weight cars. In essence, this provides four speeds with a startup gear. As Gary said, it would be better to use a higher diff ratio and retain the benefits of the 4-speed ratios, at a lower cost. The spreadsheet has another sheet with differential ratio possibilities for different ring and pinion teeth, including such possibilities as 36/11 (3.27), 32/10 (3.20), 35/11 (3.182), 31/10 (3.10) and so on.

The other approach would be to cut a new set of gears for the candidate geabox. Several of us have a spreadsheet that can provide optimum tooth numbers closely approximating the 2.50, 1.67, 1.25, 1.00, .83 sequence that would be a logical extension to the current CR 4-speed. It would seem that a shop that can cut gears could take the shafts and gears from a donor gearbox, and cut a new set to our tooth specifications without a lot of agony. This is not rocket science, or the development of a new gearbox.

I will donate the software and time to come up with appropriate tooth counts for a candidate gearbox, and possibly the costs for the prototype gearset. There a several of us here in SoCa who really want a 5-speed but are rather put off with the cost of a Voight-BGH combination. I had been working with a shop which cuts gears for vintage cars, but it looks like they got too busy and the quote they came back with was several times the original estimate so it doesn't pencil out.

Well, back into my ivory tower.

David
1968 36/7988

The T5s can easily be built up with any gear set and they are readily available in the US, so the motorsports gears are the normal choice for a rebuilt T5 in performance apps. Mine is 2.95, 1.94, 1.34, 1.0, 0.73 and I'm using it with a 4.11 LSD rear. It is not at all disappointing in a not especially torquey 1.6L BDA conversion.

Tom

Tom,

Is it possible to use the .78 5th gear from the 1352-116 or 1352-168 (SVO Mustang)? Mathematically, the ratios are better with this setup. You might notice that the drop from 4th to 5th feels a little wider with your current ratio set than with the SVO set.

Even after all these years, I can't look at a set of ratios and tell a whole lot about them. For this, I use a spreadsheet, which does all the calculations and generates all the tables and charts.

In a vehicle, I can tell the difference that changing one gear by one tooth makes, although looking at the ratio numbers would not give me a clue. I suspect that in the T5, both gears in the 5th ratio are different by one tooth between .73 and .78.

Like I said, I use a spreadsheet to do the analysis. However, this is so large (10+mb) it cannot be distributed. So I deleted everything in it that I could, bringing its size down, but it is stil, at 1.8mb, too large. So I ZIPped it, bringing the size down to 349kb. But LotusElan.net does not accept .ZIP files, so I renamed it back to a .XLS extension that is accepted.

After you download the file, rename it back to its .ZIP extension, then unZIP it. Then load it into Excel or whatever you use to display spreadsheets. It was saved in '97 format, so every body should be able to use it.

It may take awhile to get familiar with all the data and concepts. But there is a comprehensive help text that explains what all the fields are, and a lot of the theory and formulas used. I think that if someone is skilled enough to swap in, or want to swap in, a foreign transmission, they are skilled enough to understand the numbers in the spreadsheet, and will enjoy their motoring experience more understanding what is happening.

Have fun!

David
1968 36/7988