differentials

[bill308]

Dear Forum,

I want to reduce some potential excess weight on 026/5327, an S2 SE of 1966 vintage. I want to do this to partially offset the increased weight of a Safety Device's roll bar and a 5-speed Voights gear box with a 2.66:1 first, BGH Gear set, and an aluminum gear case. Hopefully, I won't be too far above the stock S2 weight.

I also want to replace the exiting differential nose with an aluminum alloy nose. It appears there are at least 2-choices for alloy noses for the English axle. The pre '65 homogated nose, light weight, and in LM25 or L155 aluminum alloy, and a later version, apparently not homologated, but possibly cheaper and of a different shape and an unknown alloy.

I plan to fit a Quiafe ATB with a 3.55 differential ratio. I expect 140-150 BHP and a fat torque curve from the engine.

Does anybody have any information, guidance, or thoughts on this project?

Also, can anyone explaine the on-road or track feel or differences between a Salisbury LSD and a Quaife ATB LSD?

Thanks,
Bill

[stuartgb100]

Bill,

You might care to google " elan mods " ........

This group/list deal with performance modifications etc, I'm sure there's plenty of knowledge there.

Regards,
Stuart.

[garyeanderson]

Hi Bill

The quaife or what ever differential slip limiting device you select will only equalize the weight loss of the alloy differential casing. If you leave out all of the horsehair insulation and alligator hide interior to offset the rollbar weight gain, it may come close to your weight target of being around stock. I am not sure about the 3.55 rear axle ratio. With a .825 overdive this over all ratio drops to a 2.93, the 3.9 works out to something like 3.22 wich seams top be a fairly decent drop in revs at highways speed.

Hi Stuart

Your too funny, Elan mods is all but dead. 26 messages in the last year and 18 were to discuss pulling the plug on the life supports. If folks want to use it thats great but this seems like the spot to discuss all Elan related (and of course anything totally unrelated).

Gary (elan mods moderator)

[TomR]

Hi Bill,

I'm just over in Vernon and have a TTR alloy nose and torsen LSD sitting on a shelf. I can weigh and/or feel free to stop by and take a look.

I've been running a 0.75 top gear and a 3.7 rear. Decided to switch to a 4.11 this build because I don't need really relaxed highway driving.

Tom Radcliff

[bill308]

Thanks guys.

To reduce weight, what I really need to do is just loose some weight, and the price is right.

I've got this thing where I really like dual purpose cars, occasional track use and a main car for my retirement years. My modest stable includes a 1978 GTS, 026/5327, a mazda MX-6, and a 1990 Pontiac Grand Prix automatic, with dents galore and a great over the road gear ratio by the way. At 80 mph, ithe Pontiac engine turns about 2650 rpm, a capable cruiser.

Hi Tom,

Thanks for the invite. I would really like to stop by. Shall I call you?

What was your experience with the 0.75, 3.77 power train? This yields an overall gear ratio of 2.83:1 verses 2.93:1, for my baseline 0.825, 3.55 power train.

Let's see:

Assuming 155x13 tires (baseline - Mich XASFF), the WSM says 18.5 mph per 1000 rpm, or 0.0185 mph/rpm in top (1:1) gear, for the 3.55:1 rear end ratio with a 4-speed transmission (1:1 top gear). So at 4000 rpm, the car velocity will be 74 mph. At 80 mph, a speed consistent with the faster interstate traffic in my area, the rpm's will be = 80/0.0185 = 4324 rpm.

With the 5-speeds on the table at 4000 rpm:

0.825 * 3.55 = 2.93; car velosity = 4000*0.0185*3.55/2.93 = 89.7 mph
0.750 * 3.77 = 2.83; velosity = 4000*0.0185*3.55/2.83 = 92.8 mph

At 80 mph and a 3.55 final drive, the rpm's will be:

80/(0.0185) = 4324 rpm for the 4-speed (direct 1:1).
80/0.0185*2.93/3.55 = 3569 rpm for 0.825 overdrive.
80/0.0185*2.83/3.55 = 3447 rpm for 0.750 overdrive.

For other ratios:
o'drive* r.ratio=overall
0.825 * 3.55 = 2.93
0.825 * 3.77 = 3.11
0.825 * 3.90 = 3.22
0.825 * 4.11 = 3.39
0.825 * 4.33 = 3.57

0.750 * 3.55 = 2.66
0.750 * 3.77 = 2.83
0.750 * 3.90 = 2.93
0.750 * 4.11 = 3.08
0.750 * 4.33 = 3.25

Tom, your selection for drive train ratios 0.75, 4.11 (3.08 overall) and my 0.825, 3.55 (overall 2.93) selection are not too different, but maybe I should seriouly consider the 3.77:1 rear end ratio (overall 3.11) which puts me really close to your 0.75, 4.11 (overall 3.08).

Bill

[msd1107]

Instead of frying your brain figuring these figures and stuff, there are downloadable spreadsheets available to do the heavy lifting.

viewtopic.php?p=87930
viewtopic.php?t=16331&postdays=0&postorder=asc&start=14

They should get you anything you wanted to know, except how to design a gear ratio set and pick the gear teeth for each gear pair.

David
1968 36/7988

[bill308]

Thanks Dave.

Spreadsheets are great and I use them daily. In this case, the calcs were pretty minimal but what I thought was really needed was some tabulated data, arranged in a particular order, to show some specific data points and some trends and comparisons. I sure wish the forum had a built in table feature, although I could upload a table.

What I learned from this little excercise was that there is a lot of ratio overlap between Tom's setup and my selection. I think Tom had it about right from my point of view. 5th should really be a relaxed cruising gear. For more performance, a 3.77-4.11:1 would be more appropriate.

Bill

[garyeanderson]

took some weights from two diffs both are 3.9, one is an open iron nose with lotus housing with shafts. 45 pounds on my scale, its not all that accurate but for this I am only using it to show the difference between the Alloy nose with the quaife torsen diff installed. There were no shafts as I used it with CV drive shafts with integrated output shafts. I added a pair of shafts and a bearing but was missing the two circlips. Close enough to 41 pounds, or a 4 pound savings for the alloy with quaife.

iron nose


alloy nose

[paddy]

Maybe the weight of the cardboard box offsets the weight of the circlips?

Paddy

[garyeanderson]

Maybe the weight of the cardboard box offsets the weight of the circlips?

Paddy

THe prop flange has been double drilled on the Iron case diff, so that and the box = net.

Gary

[r.agnew]

Wow!! Those scales are certainly high mileage !!


Rob
'71 Sprint

[bill308]

Thanks Gary.

If I understand correctly, you're saying:

OEM CWP w/spider gears with iron nose complete = 45 lbs
Quaife with aluminum alloy (LM25 or L155) nose complete = 41 lbs

Anybody have properties for LM25 and L155?

I wonder what the LSD weight penalty is?

TTR says the aluminum alloy nose saves 4.725 kg = 10.4 lbs

If these numbers are correct, the Thorsen ATB setup must weigh = ATB:

Weight balance:

OEM = al nose assy + ATB
45 = (45 - 10.4) + ATB
ATB = 45 - 45 + 10.4 = 10.4 lbs.

Quaife in a box wt. = 13 lbs.
Gary method reweigh = 13 lbs.

Pretty good agreement. It looks like and ATB setup will cost 10-13 lbs.

Any other data points?

Bill