Lotus Elan

Rear Diff

PostPost by: gav » Tue Feb 28, 2006 8:57 pm

I'm planning my next project which will be an Elan destined to be used for hills and sprints. I have the basics already - a modsports shell and chassis.

Before I get too carried away with BHP and torque, it occurred to me that I should check some basics - so -

What is the maximum torque and BHP that my 4.1 diff could take before it goes pop. Is there a better alternative? Also is there a maximum for the rear suspension?

I do intend to run on slicks - what would be a good size (I was thinking around 10" but could take 12" in the wide arches I currently have.)

Thanks
Gavin
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PostPost by: M100 » Tue Feb 28, 2006 9:21 pm

gav wrote:What is the maximum torque and BHP that my 4.1 diff could take before it goes pop. Is there a better alternative?


I know its not 4.1 but in the latest Club Lotus mag there is a pic of a 4.428 diff with HUGE 31/7 teeth compared to a 4.44 40/9 teeth. Apparently they last a hell of a lot longer in competition!

I suspect they were on some commercial vehicle version of a Ford that used the English axle.
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PostPost by: elans3 » Tue Feb 28, 2006 11:25 pm

Hi, the 4.428 with the 31/7 teeth was from the Anglia van. I know from personal experience, as in the seventies I bought just about every one in Yorkshire from scrapyards, as I used them in a succession of Escort Twincam rally cars !
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PostPost by: elansprint71 » Wed Mar 01, 2006 9:29 am

Gavin,
Give Tony Thompson at TTR or Pat Thomas at Kelvedon a ring, they will know what breaks and when!

Cheers,
Pete.
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PostPost by: rgh0 » Wed Mar 01, 2006 9:52 am

Assuming you are still using a twin cam and capacity is less than a max bored long stroke block ( no 2.2 litre blocks or nitro) I dont think you will be able to break the diff itself. I still have my original diff in the car after more than 25 years of competition and many 5000 rpm drop the clutch starts with 170hp. It is the only original power transmission component in the car

For the rest of the rear suspension you need to reinforce the chassis around the diff mounts and A Frame mounts. Stronger diff output shafts, solid rear end with CV's or U/J conversion and stronger hub half shafts and steel wheel hubs also needed. Could also be sensible to use new A frames ( Spyder make stronger ones) as I have broken one of these also.

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PostPost by: gav » Thu Mar 02, 2006 3:57 pm

Thanks everyone for your help so far and if there is more info out there, I am still hungry for it.

Rohan
I'm planning to use a modified Cosworth BD with a spec which is likely to produce between 225 and 240 BHP mut not that much torque. Is there anything else you would do with this in mind?

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PostPost by: rgh0 » Fri Mar 03, 2006 8:19 am

Gavin

No experience with BD motors but torque is what sets the limt and a BD does not produce much more torque than an equivalent capacity twink, the extra power comes at higher revs due to better breathing from 4 valves. I suspect you will still be OK with the standard 4.1 diff.

But it and the prop shaft is probably all that you should keep in the powertrain.
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PostPost by: lotusanglia1965 » Sat Mar 04, 2006 11:29 pm

I just broke an anglia van ,the diff was 4.44:1 , but definately 40/9,still unsure where the mystery strong diff comes from,will keep searching.Not that i've known many 'english' diffs break at all.
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