Sprint diff ratios

[FOX5D]

Hi everyone

I am a lucky so and so as I have 2 Elans-an S3 (1966) with a 3.77 diff and an S4 (1970) with a 3.55 diff. Both cars have the big valve spec motors and 4 speed gearboxes. The revs and vibration in the 3.77 make me want to put in a 3.55 diff like the S4.

So a couple of questions:

Is there a general preference among Elan owners for a final drive ratio to go with the 4 speed gearbox?

What diff did they put in the final version of the Elan-the Sprint?

Kind Regards

Jim

[Elanintheforest]

Hi Jim
Some S3 Elans had the 3.55 as standard for a while...the S/E Coupe of around 1967. It was an optional extra after that, and the Sprint had the 3.77.

My S3 has the 3.55, and for me it's the perfect combination with the 4 speed box.

Of course you have the option of going 5 or 6 speed now with the alternative boxes available.

Mark

[gjz30075]

3.77 came in my Sprint. Wishing for a 3.55 at this point.

Greg Z

[mac5777]

Hi, I wanted a 5 speed but the cost to lower the RPMs slowed me down. What I did do to my 66 S3 coupe was to add a 3:55 rear end, kept my semi close 4 speed and I just installed 155x80x13 tires that have a Dia of 22.8 inches and I now drive 60 MPH at a little under 3300 RPMs. And I get better gas mileage.
Hope that helps
Sarto

[msd1107]

S4s and some lucky S3s (and very determined early cars) can use 165-13 tires with +2 wheels to get better cornering as well as a useful reduction in revs. (3243 to 3154 with the common 9-32 3.55 differential at 60 mph). The 3.77 differential would go from 3445 to 3351. Your exact rev reading may vary. (The later 11-39 3.55 differential is 10 rpm less. 9-32 is 3.556, 11-39 is 3.545)

I switched to the 165-13 and +2 wheels at my first tire replacement and have never looked back. The car also has the 3.55 differential and 2.51 transmission. I never miss the so called semi-close ratio (actually a sedan gearbox), even when carpooling in stop and go traffic.

David
1968 36/7988

[FOX5D]

Hi everyone

Thanks for your responses-so far there seems to be a preference for the 3.55 which makes me feel more confident about making a change (from the 3.77). With the 3.55 diff, my S4 isn't screaming for a fifth gear but the S3 (3.77) is. I like the Elan 4 speed gearbox because it is fun and it is how it was at the time. If I had 3k I might consider the MX5 6 speed conversion, but then again I wouldn't really have a Lotus Elan, would I?

Getting hold of a 3.55 diff appears to be a very difficult task, but I notice that Burton advertise a 3.54 CW&P English Axle for ?243. Is this the right one for my S3? Any advice would be very much appreciated.

Best wishes

Jim

[bcmc33]

Hi everyone

Thanks for your responses-so far there seems to be a preference for the 3.55 which makes me feel more confident about making a change (from the 3.77). With the 3.55 diff, my S4 isn't screaming for a fifth gear but the S3 (3.77) is. I like the Elan 4 speed gearbox because it is fun and it is how it was at the time. If I had 3k I might consider the MX5 6 speed conversion, but then again I wouldn't really have a Lotus Elan, would I?

Getting hold of a 3.55 diff appears to be a very difficult task, but I notice that Burton advertise a 3.54 CW&P English Axle for ?243. Is this the right one for my S3? Any advice would be very much appreciated.

Best wishes

Jim

Leslie (512BB) seems to have plenty of them:
elan-for-sale-f2/recon-differentials-for-sale-t18555.html

[Elanintheforest]

The 3.54 English is fine Jim. It's the Escort RS2000 ratio.

Mark

[StoatWithToast]

The 3.54 was a later Ford diff, the 3.55 was a Lotus one. I think Lotus had a different case to handle the extra power they were putting through it, but I expect by the time Ford made the 3.54 (esp as it was used in high power cars) it was strong enough not to need modification, no idea about mass difference, but it is unsprung in the Elan, so I doubt a few hundred grams would make much difference (I certanly wouldn't be able to tell )

Get me, now I've read Brian Bucklands manual

[adigra]

My '67 S3 SE has had the 3.55 from new. I tend to think that it's perfect with the 4 speed.

Adi

[elansprint71]

Am I correct in thinking that there were two sets of gear ratios available as well as three choices of diff ratio? That is quite a lot of maths to do.

My Sprint came to me with a 3.77 but I have fitted a 3.55, there is also one of the others (can't remember the ratio) sitting on the shelf.

Even with the 3.55 it seems pretty busy at Motorway speeds but I'm used to stoating around in a six-speed diesel.

[msd1107]

You are correct.

The more common gearbox is from the Cortina sedan and has 2.97, 2.01, 1.40, and 1.00 ratios. The other gearbox came mainly in the earlier cars and was from the Cortina rally program. Its ratios are 2.51, 1.66, 1.23, and 1.00.

3.9 was the first differential ratio, followed by 3.55, then 3.77. 4.11 is used sometimes if you do not get on expressways. And Lotus homologated a 3.44, although I have never seen one in the wild.

There are down loadable spreadsheets at http://bit.ly/crwgUL at the bottom and http://bit.ly/auHe4d that will help with the maths.

David
1968 36/7988