MPG

[john.p.clegg]

Dear All
Can anyone help me out,my '68 plus2 returns approx 27mpg and has done for years(urban;cruising and giving it some!!),I am near completing the fuel injection project and wondered if it would be silly of me to expect 40mpg taking into account the weight of the car,the CD.the small engine size and the ability to control the mixture strength at all throttle openings???

At the moment my O2 readout shows rich most of the time.

John

[msd1107]

John,

My 69 S4 returned over 45 mpg (US) on trips, 35 mpg in city driving.

This was on Strombergs, with different needles and the needles moved down in the ring grooves. Rather lean, but the car still ran to almost 7000 rpm on a 3.55 diff.

There are several aspects to getting the best economy. One is making sure the ignition system will fire the plugs at very lean AFRs, which is key to getting the best mileage. Mapping the ignition for enough advance at small throttle openings is necessary. Then map the AFR as lean as possible once off idle and to mid throttle, and at moderate RPMs. You may have to play around with enrichening setups if your EFI allows it on throttle opening. Otherwise you will get spitting and slow acceleration. You will probably find it best to crack the throttle open gradually rather than give it a big push. This gives an effect similar to an accelerator pump, without the excess fuel.

Fuel consumption is also affected by weight, aerodynamics and tyre pressure, amongst other variables. Cutting weight by 10% would return about 5% more mileage at crusing speeds. Complicated subject.

David
1968 36/7988

[gordonlund]

John,

Apart from ensuring your engine is in good fettle and your brakes are not binding and the tyres are at the right pressure, the main factor is the weight of your right foot!!.

Takes me back a long time ago when a mate of mine was selling his Triumph Spitfire (sorry). The would be buyer enquired if the car had been flogged. My mate replied "Of course it has, he would have bought a Morris 1000 if he did not want too. It was supposed to be a sports car." I suppose a Spitfire would take some flogging to make it go, but you do take my point.

30mpg is a good figure for a +2 considering it is a lot heavier than a 2 seater Elan. I got 35 mpg on a leasurly continental tour (see my 250,000 miles posting). Spirited driving can reduce that to 25 mpg quite easily. Driven as I have seen some people drive them (fast!) this can be reduced even more.

See you soon

Gordon

[JJDraper]

I hear tales of the Zetec +2 achieving MPG figures well into the 40s when driven sedately, presumeably because of the EFI and good mapping on a rolling road. I see no reason why a Twinc can't do much the same. high gearing would certainly help as well, but you would need to check the speedo is calibrated to match or the figures would be meaningless!

Talking of which, have a care when comparing USA mpg figures with UK ones! Perhaps we should use a common measure like chains per gill...

Jeremy

[Elanintheforest]

Not as simple as that, Jeremy. There are Gunter chains and Ramsden chains. There are UK gills and US gills..

But using R chains and UK gills, I reckon that our cars get about 50 chains to the gill...sounds impressive to me. Not sure it will catch on though.

Mark

[robcall]

Ah the olde worlde- Litres/100km for rest of the us!

[steveww]

John,


This was on Strombergs, with different needles and the needles moved down in the ring grooves. Rather lean, but the car still ran to almost 7000 rpm on a 3.55 diff.

David
1968 36/7988

I would be interested to know what needles you were using. I have an S4 on Strombergs and it does tend to run a little rich at times.

[msd1107]

steveww,

Sorry for the delay. LotusElan.net seems to have had an outage, and swallowed my deathless prose. That will teach me to compose every reply in Word, and paste it into the message.

But very interesting question. The fog of thirty+ years dulls the memory. And since the car perished in a fire, I do not have it to hand.

From memory, it was B2G and B1Y (or was it B1G and B2Y?)

There are charts and spreadsheets on the web now that give all the needle dimensions. Basically, what you are looking for is needle diameters greater than standard at low throttle openings. And adjustable needles (that allow you to adjust the height of the needle)

What you will wind up with is a car that is quite cold blooded at startup and on cold mornings.

But the mileage will give your sanctimonious neighbor with a Prius pause for thought, and with a 40 year old car to boot!

There is a thread over on sidedraftcentral about tuning Weber carbs. But for best mileage you probably need a lightweight FHC car with EFI where you might get over 50 mpg.

Have fun,

David
1968 36/7988

[hatman]

you might get over 50 mpg.

Have fun,

Is this what's known as an oxymoron?

[robcall]

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :IT&ih=020

For those in need of an economical Lotus Elan

[SADLOTUS]

Here we call them Pious

[steveww]

David,

Thanks for the reply. The spreadsheet you mention is most likely mine as I took the SU one that was out there and put the Stromberg data in it.

I have tried the B1Y but it gave a flat spot around 2500 rpm on small openings. The B2Y is richer than the B2AR I am currently running. The B2G will be too lean at the top end for my Elan's motor, it has been tweaked a bit The head is ported, there is a large bore exhaust and the carbs have ram pipes and high flow filter. Oh and the cams are custom made from Piper.

I have been told possible alternative needles that are close to B2AR: B1DG B1DF but I have not had chance to try them out yet.