5-Speed Candidate Conversion Chart

Elan Discussions
21

John,

You could use a 3.54 differential ratio to “lift” 1st gear. All ratios would be “lifted” in proportion. You would still be left with the wide ratio drop between 1st and 2nd.

Consider whether your car can pull the 5th gear to peak power RPM in 5th (one way to determine gearing). Generally speaking, a FHC with engine modifications should. A DHC probably can’t. The average driver doesn’t care, they are looking to reduce RPMs on the highway.

An earlier post on April 12, 6:25am, has a downloadable spreadsheet that allows you to input your car’s tire size, target RPM, gearbox ratios and see speeds for a variety of differential ratios.

And a post on April 12, 12:18pm, has a downloadable spreadsheet that has more comprehensive tables and charts. It also has comprehensive documentation so you might come to understand some of these issues.

Admittidly, most people do not sweat the details, and drive what they have. I always thought Elan owners were more technically oriented, and would be interested in reading about some of these things.

David
1968 36/7988

22

I am very much the “average driver” you describe. My new engine would be very happy at 70mpn/3000 RPM instead of the 4000 it turns now. I don’t care too much about the 4th-5th gap, so a .75 5th, and something like the CR 1-4 ratios I am so used to, would do nicely. It would be interesting to see what speed the car could do in 5th but it’s not something I’d do every day.

Anyway, sign me up as a very interested consumer for this effort.

23

My old 89 Mustang LX 5.0 would pull a higher top speed in 4th gear that it would in 5th. This was a 140,000 mile car with the Borg Warner T5 that we have been talking about in some of these posts. I think the top speed difference was 10 or 15 mph slower in 5th. Ford, I am sure, did a lot of testing to make sure that they got it right. That said it would do 80 in any of the top 3 gears. Anything that we as owners come up with will have none of that testing. It will be, “I think it will work ok with that .73 overdrive” but until someone puts it in their Elan they won’t really know. We have a lot of folks interested in this “multiple 5 speed project”, some with bone stock Twin Cams and others with 2 liter Cosworth BD’s. I guess what I am saying is its going to work better in some Elans than others. If you did all of the work and spent all of the money and every time you hit a 3 percent grade (3, 4, 5 percent take you choice) you had to drop down to 4th you may be a tad disapointed.

Gary

24

Gary,

Very good point. Some manufacturers gear the car for top speed in next to top, and use top for reduced revs when cruising, better fuel economy, better EPA ratings, etc. If the engine is peaky, the driver will have to downshift on an upgrade. But hey, I saw this in my rental car in Europe, where my economy car would hold 140+ km on the straight in 5th, but required a downshift to 4th on any but the most gentle hill.

A previous post lotuselan.net/forums/viewtopic.php?p=63669 analyzed what potential final ratio might be needed for our Elans in various stages of tune and various tire sizes.

This post lotuselan.net/forums/viewtopic.php?t=15596 has a spreadsheet that allows the potential top speed of a vehicle to be estimated.

An earlier post in this thread had a downloadable spreadsheet that gave speeds for different differential ratios and gearbox ratios given the cars’ tire size and RPM. So, put in a proposed ratio set, scan down the differential ratios to get the closest matching one.

And another post lotuselan.net/forums/viewtop … c&start=74 went through some of the issues in converting a foreign transmission for use in the Elan.

But the impression I get is that the majority of people don’t care about these details. They want to remove their old transmission, put in the replacement (of course with the aid of a step by step with illustrations installation manual), and have a more relaxing drive down the road.

So when (and if) we get what appears to be an acceptable project defined and bid, we can agree upon a set of ratios. I can create a fitment guide so that the sophisticated user can determine an appropriate differential ratio for their expected useage. During the prototype phase install and take pictures in various car configurations to produce an installation manual.

The impression I get when looking at other cars user groups is that we have better tools to define, model, and evaluate potential solutions. Others seem to take whatever transmission is available in the breakers yard, hack and cut and adapt as necessary to get it to fit and get on with life. Hopefully, we have the capability to get to a technically elegant solution in the philosophy of Chapman.

David
1968 36/7988

25

Hi David
I should say that all Elans are different, whether delivered from Lotus or modified by one of its many owners. Power being anywhere from 95 bhp (maybe less if it needs work) to over 170. Gearboxes lets call it 4, wide, semi close, ultra close and the 5 speed Maxi box. Differentials from the factory were 3.9, 3.77, 3.55. Various Ford crown wheel and pinions of 4.1, 4.44 maybe some higher too. We have Plus 2’s and Elans weighing from 1250 lbs. to over 2000 lbs. coupes, DHC, roadsters, plus 2’s chopped plus 2’s.

The progression of 1st gear ratios from Ford was something like 3.54 sedans, 2.97 sporting, 2.51 rally or race, some special 2.29 back to shorter 3.65 for nearly every thing. Russ told me once that he didn’t want a 1st gear any shorter than a 2.8x for his plus 2. You, Andy, Tim, myself and others would probably not go for anything less than an ultra close with a .8x.
Custom gears are great if we had a one size fits all but that isn’t the case. The best we can do (in my lame ass opinion) is to take a box that is relatively common that has good support from the junk yards and aftermarket and get it to fit. A modified T9’s certainly fit the bill in England but 1500GBP plus at least a 1st gear swap for 300 or 400 more, installation, then add the shipping to the U.S. and it doesn?t work for many/most Elan owners. The T5 has almost as many issues as do the others (AKA Alfa, Isuzu, Toyota, Ford MT75). This is getting close to dead horse time, unless someone with deep pockets steps up, it is dead.

The custom cut Crown wheel and pinion is the only (semi thrifty) option and its not perfect or anywhere near. No one seems to think much of it so that will be a one off for an individual solution. A 3.10, 3.18 3.25, 3.36, would get most of what folks want and would work with most combinations of 4 speed we currently have and be 1/2 to 1/5 of the cost of some of our current 5 speed options. Your spread sheet gives 60 to 65 mph at 3000 rpm for those ratios with a 165 tire. At the other end in 1st gear (worst case 2.51) 8 to 8.7 mph/1000 rpm, both a little tall but the 3.77 gives 7.2 for the same combo. With a semi-close and 3.77 diff it works out to 6 mph/1000 in 1st and 53.7 at 3000 in 4th. My pockets are inside out for any of it, I am going to go out and drive my Elan this summer. The most I expect to get done is get my ultra-close box reassembled for installation next winter.

26

Your entry is the most interesting in this interesting thread! When did Alan Voights actually agree to sell his T-9 conversion to you? I’ve had a few telephone conversations with him over the past six months and all I hear is how he will be back in production some day. I too have dangled the option of consolidating the gearbox with a container of other parts so he does not have to worry about packaging for a trans-Atlantic trip. This didn’t seem to help either.

27

This gearset sounds like the Holy Grail for my situation - with a 3.9, not the 4.11. 1-4 just slightly wider than my CR (I can live with that, I think) and the all-important 3000rpm highway 5th.

28

Hi Gary,

You make a very good point that there a wide range of Elan cars and owners, with different, and opposing, desires.

However, engineering always has to face these issues. And management has to resolve the personel issues. If we engineered a solution that satisfied 3 sigma or 95%, would there be a substantial reduction in demand? Or would this last 5% sign up for the benefits of a properly engineered solution even though they might have to slightly adapt their driving style? Would we care if they didn’t?

Since I am mechanically inept, I will shy away from a solution that has me drill, fabricate, cut, weld, machine, mill or any other skills oriented task.

But after reading this thread, I might be tempted to order a Voights kit, call Brian at BGH and order a E6/E7 gearkit, order an aluminum case from Quaife, and get a XR4ti maintenance manual on CD off of ebay (which has 60 odd pages on disassembling/reassembling the gearbox).

Then in theory, it says, I could merge Voights kit with the BGH gearkit in the Quaife case, follow Voights installation instructions and get the kit in the car.

Then I have non-standard components from the engine block to the drive shaft.

The other tack is to machine a gearset to our specifications so we have Lotus shaft lengths and splines, cast a gear case so we have 2000E bolt pattern and frame mounting boss.

The rest, as they say with a casual wave of the hand, is details. It will all plug and play.

The important thing is to get an acceptable quote from a gear cutter for the gearset and a foundry for the gearcase that, in estimated production volumes, pencils out. I had done this earlier, but my contact got sick, the shop got busy, so their written quote came in several times higher than expected. So, on to the next one. Anybody with contacts can help the group effort by getting the gearcutter/foundry and us together to talk and make a deal. Email me with names/phone numbers/email addresses.

I have met with other Elan owners here in SoCalif who have declared they are going to fit a 5-speed come hell or high water. And they have the mechanical skills to do this. So if I can’t do the job properly, I may get a hack job and the rest of the Lotus community will lose another opportunity to get a properly engineered 5-speed.

Well, back to work.

David
1968 36/7988

29

David,

The 2.75/0.82 setup appears really good to me. It’s about midway between the close and semi close gear sets. The BGH 2.75 first (there is also a 2.66 available) gear should work well for both the Elan and +2. I can get underway with almost no throttle, just carefully engaging the clutch, with the semi close 2.97, 3.55 rear, and 165x13 on 5.5 inch Panasports. This is particularly useful when on a multilane highway, in barely moving traffic. The state of engine tune was a modest CR, Webers, low inertia flywheel, big valve intakes, degreed in Sprint cams, Port matching to the isolators, detail porting in the valve throat area, and it’s path just up stream, but below the guide. The engine had very good driveability and pulled well up to the elevated red line.

Bill

30

CBUEB1771,

I purchased this T9 conversion from a fellow chatter. It had been stored for a while, but was unused, and with his cooperation I was able to make the shipping arrangements work well.

Bill

31

Bill,
Thanks, this ties together now.
Russ

32

how about this as a solution? Agreed it would require some chassis mods to fit (access hole from below?) but it would retain the original ratios and gearstick/position and delightful shift quality, the excess weight could be countered by the various alloy gearbox replacement parts (tail housing/bell housing) and would give the required “fifth gear”, an added advantage could be an eight speed close ratio box ala TR6. Not sure of the cost, however I’m sure an enterprising soul could duplicate the front case arrangement and modify a Laycock overdrive unit themselves?

Mark

33

Mark,

Very interesting idea.

Usually, it is difficult to use an overdrive on more than one ratio because you get some strange feeling drops between gears.

But the wide ratio transmission (2.97 1st) is actually relatively amenable to having OD on all gears.

If you could locate an OD with a .834 ratio, this would produce ratios of 2.97, 2.476, 2.01, 1.675, 1.4, 1.167, 1.00, and .834.

If you download the spreadsheet from lotuselan.net/forums/viewtop … c&start=14 and enter the above 8 ratios, it calculates a Figure of Merit of 61.4, a surprisingly high figure, and better than most of the 5-speeds being considered.

The Figure of Merit is a mathematical calculation, with a maximum value of 100 and no minimum value. As a frame of reference, the BGH E7 with 2.75, 1.75, 1.26, 1.0, and .82 has a FoM of 84.1. The T5 mentioned by TomR of 2.95, 1.94, 1.34, 1.0, .73 has a FoM of -23.0 (not good at all)

So much for speculation.

David
1968 36/7988

34

Generally the use of the Over Drive is limited to 3rd & 4th gears as the OD unit can not handle the torque in the lower gears. I have owned a couple of MGs with the OD arrangement and it worked very well. Due to the MG and Triumph markets there is plenty of support for OD units.

This is an avenue of thought that should see some more research.

35

I remember the OD in the MGB.
Very handy location of the switch on the gearknob-making for a natural shift action.
I am wondering about switch options here-gearknob/dash/steering wheel?

36

Under the or on the throttle pedal would work nicely too, just like the kick down on an automatic transmission. The O.D. unit would take most of the space that thecurrent propellor shaft occupies. The shaft length is 22 inches center of u-joint to u-joint.

gearvendors.com/index.html

No bolt on applications but lots of info. Torque would not seem to be an issue on these units, at least as far as the Twin Cam is concerned.

37

An other possible starting point

overdrive-repairs.co.uk/services.html

38

Footswitch is a good idea-less obtrusive.
Along those lines I’m thinking of the old fashioned headlight dipswitch foot control.

39

A bit of Google and I see that an overdrive unit was fitted to Ford Type 3 gearboxes on Scimitar and TVR.

40

I just ditched the foot dipswitch for the column-mounted variety, in part so I’d have a place to rest my left foot. I would mount an overdrive switch higher on - not the firewall, it’s actually the wheel well.

So if we go down this road, someone has to engineer the mating of the OD unit to the rest of the transmission. Does it hook up to the existing tailshaft and housing, or is the housing truncated behind the shift lever and speedo drive? What about the speedo? - it has to know how fast the driveshaft is turning. And so on.