Lotus Elan

Eight years of fuel consumption records

PostPost by: RotoFlexible » Sat Jan 02, 2016 3:19 pm

When I put the Elan back on the road in 2008 following a complete overhaul, I started keeping a record of fill-ups. I recently transferred them all to fuelly.com - you can see them here. There are some unrealistic highs and lows in the data due to incomplete fill-ups or maintenance, but overall the number should be pretty accurate. Bottom line: 17,164 miles, 28.1 MPG, which works out to 610.8 gallons of fuel flowing through (or evaporating from!) the Webers.
Andrew Bodge
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I love the sound of a torque wrench in the morning. Sounds like... progress.
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PostPost by: TroonSprint » Sat Jan 02, 2016 3:35 pm

Since you are in the USA, I guess your figure is in US mpg. For us Brits that converts to 33.7 mpg in Imperial gallons (I hate the word imperial). Pretty good I should say. Well done for keeping the records!

Mike
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PostPost by: john.p.clegg » Sat Jan 02, 2016 4:01 pm

Sounds familiar,mine was 28/29 mpg ( UK ) till I fuel injected it...

John :wink:
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PostPost by: stevebroad » Sat Jan 02, 2016 7:08 pm

So, what is it now?
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PostPost by: john.p.clegg » Sat Jan 02, 2016 8:42 pm

Now I'm getting 37/38 mpg,aiming for 40 mpg,still with "spirited" driving....

John :wink:

P.S. You don't need it rich all the time-just when you need power,cruising is another thing....
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PostPost by: bill308 » Sat Jan 02, 2016 11:51 pm

Also remember most usa fuels are mixed with up to 10% ethanol. So a built in loss of 2-4%.

Bill
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PostPost by: LI-599 » Sun Jan 03, 2016 6:06 am

My S4DHC (Webers and sprint specs) returns 40 to 45 mpg consistently, and all drives are spirited especially on our great roads here in Vic, Australia. Ian
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PostPost by: john.p.clegg » Sun Jan 03, 2016 9:21 am

In that case I would be V careful as you are probably running V weak at some throttle openings......Maybe you could licence the fuel settings to Ford or GM etc.etc.

John :wink:
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PostPost by: martynbrown » Sun Jan 03, 2016 12:32 pm

This discussion has prompted me to search out two test reports which were done by Motor magazine. The first was a test of an Elan S4 SE with Strombergs in 1970 and the second is of an Elan Sprint in 1971. I've attached the fuel consumption curves from these reports. Note that the blue line on the S4 SE graph is simply the Sprint curve that I transcribed years ago for comparative purposes.

Regards

Martyn
Attachments
elan-sprint.jpg and
elan-s4-se.jpg and
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PostPost by: john.p.clegg » Sun Jan 03, 2016 12:47 pm

Martyn
I think you've got the photos reversed,that being said 46mpg at a steady 30 mph sounds Lotus good to me..

John :wink:
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PostPost by: john.p.clegg » Sun Jan 03, 2016 12:50 pm

"FUEL CONSUMPTION
Touring ( consumption midway between 30mph and maximum less 5% for acceleration 30.7mpg,Overall 25.4mpg"

John :wink:
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PostPost by: Chancer » Sun Jan 03, 2016 12:56 pm

Is the second graph for Weber carbs?

If so it disproves the popular opinion that a Stromberg equipped car gives better fuel economy.

Mind you that probably was true as in the day the majority of weber carbs were unbalanced, and poorly set up with too rich a mixture and probably wrongly jetted.

If they were well set up they very soon went out of tune.
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PostPost by: Chancer » Sun Jan 03, 2016 1:07 pm

You can get superb economy from a pair of correctly set up and jetted Webers, the trick is to have a small throttle body size, aux vents and chokes so that the main jet circuit comes in at not too high an engine speed, that way you can have a good idle and transition mixture and a richer main jet mixture for acceleration and high revs this gives a flexible responsive and economical engine but this does ultimately restrict the breathing and top end power.

I had a Zetec in a Caterham on webers not specified by me so I had to live with them and make the best compromise, the problem was ithe main jet circuit did not come in fully until 5000rpm and jetting for good economy for town and mid range driving left it seriously lacking on WOT mid range when the engine could developing good torque but needed a richer mixture to do so. That car gave superb economy in town and at cruisng speeds when I ran a leaner idle jets and emulsion tubes but was a pig at higher revs and I risked detonation.

I only found out by chance when one of the aux vent screws fell out and the aux vent rotated blocking of the main jet fuel outlet on that barrel, it ran fine up to 5k revs on a small throttle opening but would misfire, on that cylinder only on WOT.

I had to live with compromise settings as I didnt have the money to change the carbs, they were Spanish Weber 45's and also had terrible progression drillings.
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PostPost by: martynbrown » Sun Jan 03, 2016 1:12 pm

John

I haven't attached photos to my postings previously so I wasn't sure in which sequence they would appear. I've just checked that the correct filenames appear when you hover over them. Thanks for pointing it out.

Regards

Martyn
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PostPost by: martynbrown » Sun Jan 03, 2016 1:27 pm

Just to clarify, the upper graph is for the Sprint with Webers and the lower graph is for the S4 SE with Strombergs (with the Sprint curve superimposed in blue).

Does anybody have an equivalent test report for an Elan SE with Webers? That would give us a fairer comparison of Strombergs to Webers.
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