Lotus Elan

Consensus on a +2 with 3.5 dif

PostPost by: Greg Foster » Sun Dec 17, 2017 12:36 am

I am considering installing a 3.5 dif with a quaiff unit in my +2S130. Has anyone done this? Any repercussions other than to the wallet? The car will also have a stroked engine producing a minimum of 140hp and stock trans....
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PostPost by: prezoom » Sun Dec 17, 2017 1:29 am

I installed a 3.54 about 2 months ago, though the engine is a 2L Zetec. I did notice a bit of difference in acceleration over the 3.77 that was removed, but not enough to get excited about. It is still faster than my standard engine S2. Freeway cruising is a bit more relaxed, Currently in process of installing a close ratio gear box in the P2, which will probably make it a bit slower in the lower gears. But, I think I will enjoy the longer 1st gear. Can always change it back if I don't like it.
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PostPost by: rgh0 » Sun Dec 17, 2017 1:33 am

My Plus 2S 130/5 has a 3.5 diff. That combined with the 5th speed makes it a great touring car. The relatively low first gear means no problems getting it off the line either with just the standard big valve engine. i do however run smaller diameter 175/60 13 tyres which gears it down somewhat compared to original tyres with the same combination

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PostPost by: david.g.chapman » Sun Dec 17, 2017 9:43 am

If you want to install a 3.54 diff to get quieter motorway cruising, you could try a crude test to see how it would benefit you.
Just run at 0.93 times your normal cruising speed in top gear and try and decide if the conditions are better enough to make the change worthwhile.

I found that by installing an extra exhaust box the only thing that changed was the pitch of the engine - it was'nt any quieter for me.

Individual exhaust resonances could make it go either way perhaps.

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PostPost by: Greg Foster » Sun Dec 17, 2017 9:52 am

Thanks,
Much to consider
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PostPost by: Orsom Weels » Sun Dec 17, 2017 10:38 am

As Dave has implied, the differences/advantages are quite small compared to the work & expense involved.
I looked into this myself a while back & worked out that with the std 4 speed box, it would drop the rpm's by just under 200 at 60 mph. Using an average of tyre manufacturers declared rolling radii I worked out the effect different tyre sizes & diff ratios had on overall speed & rpm patterns, it may be of use in making your decision
Speed-RPM table.doc
(10.5 KiB) Downloaded 57 times


Regards, Tim
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PostPost by: Bigbaldybloke » Sun Dec 17, 2017 6:11 pm

I changed my diff from the 3.77 to the 3.55 soon after I bought the car over 40 years ago as I was doing around 1000 miles a month up and down the country. I found it did make a difference even though it was only just over a couple of hundred revs difference at motorway speeds, and didn’t really notice any loss of acceleration. I’m just rebuilding the car now after it’s been off the road for 30 years and have left the 3.55 in although I still have the original under the bench. Mine is an early plus 2 with four speed box but it had been fitted with a big valve engine when I got it. I had this engine rebuilt at the same time I changed the diff, (rebored +30”, tuftrided, balanced, flywheel lightened a bit etc.) the head gas flowed and it had about 135 bhp when first built. Hoping to getting running again soon, be interesting to get it on a rolling road to see what it has now.
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PostPost by: pauljones » Wed Dec 20, 2017 10:18 am

I have a fuel injected twink, 105 bhp on the dyno. With the 4 speed and 3.54.. i find its ok.
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PostPost by: JJDraper » Sun Dec 24, 2017 5:10 pm

I ran a 3.55 for a few years and it was a help on long journeys, especially on the autobahns, but I found older mountain passes difficult where I had to use 1st gear to get round hairpins, or starting on steep slopes. I occasionally had to take a run-up to make the slopes, or slip the clutch (which is horrible).

In day to day use I found it blunted the acceleration slightly in my sprint spec +2, so when I had the opportunity I switched back to a 3.77. On balance, it depends what you intend to use the car for. If you can, keep the old 3.77 and switch back if you don't like it.

Sorry I can't be more categorically in favour one way or the other!

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PostPost by: pauljones » Sun Dec 24, 2017 8:24 pm

Jeremy,

I think i posted a similar response in a topic. It does dull down the A road blasting. Im eventually going 1800 zetec so 150hp and torques should bring the fun factor back to par.

Its still livable tho, i wonder how it would be the other way, with a 3.99?
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PostPost by: prezoom » Mon Dec 25, 2017 12:53 am

My S2, on 175"s, has a 3.9, mid close, and a standard 105hp engine. To keep from getting run over on I-5 coming back from Cars & Coffee, means 85+mph and 5000+rpm. There is another 3.54 in the box for that one, when time permits. Which will probably mean building up a 1700.
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PostPost by: Greg Foster » Tue Dec 26, 2017 11:20 am

Still pondering this. Quite a few opinions and for myself no experience one way or the other. I am going to rebuild a spare diff and install the 3.5 with the quaif. That means my 3.7 will still be there if I am totally opposed to the change. The 3.5 may be better in my s3 elan as versed the +2. Of course neither car will get driven daily nor on extended trips. Spirited runs yes but no continuous competitive rallying is expected. I did notice in my +2, when driving 55 to 60 mph that (not) wonderful drone from the exhaust (which by the way is stainless) and that was what I would like to minimize. Other items I have noticed are;
vibration drone at highway speeds in my s3 AFTER I installed the full rubber motor mounts. This car has a mild steel exhaust which is 25+ years old and still doing well, it does get oiled regularly via the natural oiling tendencies of Ford/ Lotus twin cam technology.
I owned an early MGB with a full SS exhaust which resonated at the most wonderful time of 60 MPH speed and drove me crazy.
I do think that mild steel is less likely to create those harmonic overtones that occur with the more brittle S.S.pipe.
Noise, vibration one consideration
Comfort, drive-ability, and sheer fun factor the other.
I do know that when either elan, driven in the spirited manner which normally besets me, tends to lift a rear wheel while cornering, the loss of forward momentum slightly stifles the thrill. Having a LSD setup would encourage continuous power to the macadam no questions asked...
Still with a dilemma.....
Greg
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PostPost by: elanner » Tue Dec 26, 2017 12:52 pm

If you're still pondering the choice I would add my 2c to say that I was surprised how much my 3.54 diff improved the fun/usability of 3rd gear when driving around town.

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PostPost by: gus » Tue Dec 26, 2017 2:10 pm

If you dislike the drone, make sure your spare is bolted in place and that your trunk floor and carpets are in.
The plus two is always a little slow off the line, I cannot imagine wanting to make it slower. It think I pull away from a stop more often than I drive long enough that the noise bothers me.


While I would love a 5 speed, a bigger radio works just as well.....
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