Lotus Elan

Diff ratio - hill climbing - need higher revs on corner exit

PostPost by: dunclentdr1 » Sun Jul 07, 2019 10:09 am

I run my S1 GTS in a hill climb championship - the engine performs very well at 35000 rpm and above but out of a couple of corners my exit revs in second gear are lower than that - consequently the car takes a few moments to really get the power down.

At the moment I am running a 3.9 diff with Quaife ATB and a close ratio gearbox - does anyone have suggestions or experience with an alternative diff that would give me higher exit revs on slower corners?

Thanks

David
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PostPost by: rgh0 » Sun Jul 07, 2019 11:17 am

3500 rpm or 5000 rpm ? i doubt 35000 rpm :lol:

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PostPost by: dunclentdr1 » Sun Jul 07, 2019 11:47 am

...good spot Rohan - boy it loves to rev but haven't got to 35000 yet - gets going above 3500, more so from 4000 prm.

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PostPost by: baileyman » Sun Jul 07, 2019 12:04 pm

Not enough RPM headroom for 1st gear?

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PostPost by: rgh0 » Sun Jul 07, 2019 12:08 pm

dunclentdr1 wrote:...good spot Rohan - boy it loves to rev but haven't got to 35000 yet - gets going above 3500, more so from 4000 prm.

David


Try a 4.1 or 4.4 diff. What size tyres are you running ? Can you use a lower profile.

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PostPost by: englishmaninwales » Sun Jul 07, 2019 12:34 pm

Yes, I’d agree, consider changing to a 4.1 or 4.4.

However, with these ratios you might find your unweighted inner rear having a tendency to spin up on exit of tight corners, so moving from an ATB to a properly set up plate LSD can make a very nice combination.

Having said that, I have no experience with my Elan the hills, but this was a combination in my hillclimb Caterham (4.1 and a low preloaded Titan LSD) and was a significant improvement over a 3.9 and a Quaife ATB.

There maybe other issues relating to this set up in an Elan, others with experience will be along to point out.
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PostPost by: bitsobrits » Sun Jul 07, 2019 2:50 pm

If your exit speed in a corner is below 3500, why not just downshift before the corner?
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Formerly:
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PostPost by: dunclentdr1 » Sun Jul 07, 2019 3:50 pm

...have tried that - it is a hairpin with very heavy breaking and a lot of steering input required so I'm busy and also dropping into first takes down my speed around the bend via the engine braking...
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PostPost by: Foxie » Sun Jul 07, 2019 11:24 pm

I swapped the 3.55 diff for a 4.55 in my Plus 2 in April.

It's now just perfect for hillclimbs (I won the Irish Historic Championship last year, looking good again this year !) but on normal road driving I'm at 3.5K at around 60mph.

So now I'm thinking I need to swap out the 5-speed T9 with the 4.55 for a 6-speed with the 3.55 ! :(
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PostPost by: rgh0 » Mon Jul 08, 2019 10:08 am

A lower profile tyre is equivalent to a higher diff ratio. If not using a 175 / 60 x 13 tyre I would try that. Yokohama A050R soft compound would be ideal for hill climbing

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PostPost by: englishmaninwales » Mon Jul 08, 2019 2:14 pm

What class are you running? As you will know that will dictate any tyre change, for example Rohan’s choice Yoko 050 medium or soft are MSUK list 1c, so not eligible for roadgoing production (list 1a only) but otherwise ok in modified production / libra classes (dunno about historic classes), but would be out gunned there by other super soft hillclimb tyres (eg Avon or Kumho) or slicks.
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PostPost by: dunclentdr1 » Mon Jul 08, 2019 8:05 pm

...road going hill climb class so need a tyre on list 1a or 1b.

Recommendations welcomed...

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PostPost by: englishmaninwales » Tue Jul 09, 2019 8:59 am

What tyres are you presently using?
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