Lotus Elan

Wide-ratio 4 speed box: best solution or impossible dream?

PostPost by: msd1107 » Sat Jul 02, 2011 8:17 pm

The standard gearbox (2.97 1st) with a 3.5 (3.54) CWP should be adequate for most purposes.

I believe that the S3 SE came that way, and the CR (2.51 1st) was reasonably popular with the 3.55 for continental high speed touring.

I personally used this combination. It was suitable, even with LA's mobile parking lot morning commute. This is not exactly suitable for those drop clutch drag strip starts, but a slight clutch slip with the throttle just off idle gets you started with no drama, and I had no problem with rotoflex wind-up issues.

Reducing cruising RPMs more than the 3.77 to 3.55 change would require adapting in an OD 5-speed, which has been covered to death here.

Just my opinion.

David
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PostPost by: Sea Ranch » Sat Jul 02, 2011 9:21 pm

Whoa . . . I take it all back . . . !!!!!!!

Finally got out on the freeway with my car! :mrgreen:

Canada Day (July 1st, after Queen Victoria signed the British North America Act in the spring of 1867) on Friday and my son and I went to a "football" match (as you Brits call it) in Richmond. Took the long way there (along "river roads"; Stu, you know what I'm talking about); very pleasant. But on the way back I took a freeway stretch for about 10 minutes only and the car was EXCELLENT! First time since getting the thing through inspection and licensing. It fairly hums along at an indicated 70mph (which is who-knows-what, but I was keeping up with all traffic and passing many), didn't feel busy and was a great/exhilirating experience.

Which is what you said (or shouted), Ross!! Can't wait to get out on the road again (road trip on the Hope-Princeton highway next week, through the "mountains").

Thanks for all the insights offered here. As I had suspected, the construction of the box dictates a direct/1:1 for fourth gear. That about explains it for me. If fourth gear stays the same, then the first three ratios are just fine, if not perfect, for me.

Interesting experiment, though, Paddy and Ant (converting 3rd to an overdrive and swapping around the linkage) . Thanks for mentioning that. I think I'll do a bit of digging on that to satisfy my curiosity.

Randy
Last edited by Sea Ranch on Tue Aug 16, 2011 8:54 pm, edited 1 time in total.
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PostPost by: Sea Ranch » Sat Jul 02, 2011 9:31 pm

msd1107 wrote:The standard gearbox (2.97 1st) with a 3.5 (3.54) CWP should be adequate for most purposes.

I believe that the S3 SE came that way, and the CR (2.51 1st) was reasonably popular with the 3.55 for continental high speed touring.

I personally used this combination. It was suitable, even with LA's mobile parking lot morning commute. This is not exactly suitable for those drop clutch drag strip starts, but a slight clutch slip with the throttle just off idle gets you started with no drama, and I had no problem with rotoflex wind-up issues.

Reducing cruising RPMs more than the 3.77 to 3.55 change would require adapting in an OD 5-speed, which has been covered to death here.

Just my opinion.

David
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Thanks, David. I will have a 3 hour run coming up; half on freeway and half on winding mountain roads. Will get a good feel for it then. But tend to agree that living with the four speed, and lowering revs (if desired) through diff ratio change and the tallest tires available will be the best compromise between shifting quality/durability/cost and avoiding the headaches of transplanting a 5 speed.

Randy
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PostPost by: msd1107 » Sat Jul 02, 2011 10:36 pm

Good point about tire sizes, Randy.

The early Elans with 145-13 tires had roughly 939 rev/mile. S4's and later used 155-13 and had roughly 912 rev/mile. +2s used 165-13 for 887 rev/mile. S4's can usually be fitted with the 165-13 tire. Earlier cars have much more difficulty.

70 series tires usually cannot fit on the S1/S2 cars. S4's often can take 175/70-13 tires for 917 rev/mile. 185/70-13 is the replacement for 165-13 and has 893 rev/mile.

So the tallest tire is the 165-13 tire. With a 3.55 CWP, 4,000 rpm with 145-13 tires gives 71.9 mph. This changes to 74 mph with 155-13, 76.1 mph with 165-13, 73.6 mph with 175/70-13, and 75.6 mph with 185/70-13.

Looking at it another way, 70 mph is 3893 rpm with 145-13, 3783 rpm with 155-13, 3679 rpm with 165-13, 3805 rpm with 175/70-13, and 3705 rpm with 185/70-13.

If you went to the 185/60-13 tire, 4,000 RPM gives 70.6 mph, 70 mph is 3964 rpm which is lower effective gearing than the early, small 145-13 tires.

People using 60 series tires usually upgrade to 185/60-14 wheels and tires for 73.8 mph at 4,000 rpm or 3794 rpm at 70 mph, not quite as good as with 165-13 tires.

If you have bolt-on hubs, you can go with lightweight Superlight wheels and use 185/55-15 tires for 74.6 mph at 4000 rpm or 3751 rpm at 70 mph.

Many options.

David
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PostPost by: Sea Ranch » Tue Aug 16, 2011 9:14 pm

Finally getting back to this topic after a busy summer. And a little report on my 7 hour round trip through the mountains:

:mrgreen: Really enjoyed it. Don't have a gps to check my real road speed that way but an indicated 70 mph on the speedo is definitely faster than our 100 kph speed limits and fast enough for my cruising needs. At an indicated 60 mph, the motor and driveline are working against each other (in terms of vibration frequencies) and the whole car fairly "thrums" in a terrible way. But at indicated 70 mph, it settles right down and feels like it could cruise there all day.

For myself, I still wear earplugs on the highways/freeways (old habit from motorcycling days) (expect to get a blast of comments on my "wimpy-ness", but I'm saving my eardrums for music :lol: )

Randy

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PostPost by: worzel » Wed Aug 17, 2011 9:03 am

Hi

Just a bit of info from the distant past!

The comments about different gearsets in a 4 speed casing remind me that in the late 1970's an outfit called Godfrey Hill Gearboxes (London based I think) used to do something similar by offering 3 "normal" gears plus 4th as an overdrive. Sorry I don't know the costs but it probably wasn't cheap! At that time I was actively looking at ways of upping the gearing and went down a number of blind alleys- the most promising was the ad in Motorsport from a guy selling a S4 fitted with a Hillman Hunter overdrive (because this apparently was the smallest overdrive on the market). I rang him and he told me it had been fitted without any chassis mods. He was emigrating so was selling up- I offered to buy the plans on how to do it from him but when I called him back a few days later his line was disconnected. About 2 years later an ad appeared in Exchange and Mart offering "Overdrive" gearboxes for elans- I ranf g the firm (can't remember their name but I think it was actually "Overdrive Gearboxes"- they were in North Lancashire. They adapted 2000E boxes as fitted to some (a few) Ford Transits which apparently came as std with electric overdrive. I believe that this point about Transits is actually correct and not an "urban myth". On another note somebody on the forum recently said he'd just missed a ZF 5 speeder adapted for an elan- if it's the type of gearbox I'm thinking of it only raises 5th from 18.5 to 19.8 mph/1000 revs. I think it's the same type of box Vegantune used to offer. A lot of money for only a small gearing increase.

Regards

John
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PostPost by: gjz30075 » Wed Aug 17, 2011 12:49 pm

Ok, Randy, to recap: what diff ratio and what size tires are you running? Looks like a fantastic trip you took.

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PostPost by: Sea Ranch » Wed Aug 17, 2011 5:43 pm

'Twas indeed great, Greg!

But I don't know my car's ratios yet. Have not got the rear wheels free at the same time and done the rotational test/measuring yet!

I do believe the box is the typical semi-close ratio (as it certainly seems close), but haven't observed the rpm change from gear to gear (my tach is often bouncy, presumably due to the electronic ignition installation).

All I can say for sure is the tires are 185/70-R13 (Kumho, actually).

Wish I could say more, but for now I haven't done much calculating. But I can say I'm quite satisfied with the ratios; my issue now is with the noise and vibration from my driveline, which will be sorted when I get around to pulling them, I guess.
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