poor fuel consumption

[bill308]

Andy,

It would be very interesting to compare the setups of both sets of carbs, especially:

idle jets
main jets
main air corrector
chokes
auxiliary venturi
pump jets
pump cam
float level

Also it would be nice to know:

curb weights
CR
cams
tranny ratio's
rear end ratio's (pinion/crown wheel)
Cd (drag coefficient)
tire types, sizes, and normal pressures
approximate mpg

Some of this stuff would be nearly impossible find, like Cd, but it would be nice to know.

Also, do you drive the cars in the same manner? How would you describe your driving style?

Are the cars basically up to the same standard mechanically and how would you describe it?

Sorry, I don't mean to put you on the spot, but if you could supply some of this information, it would be interesting.

I bet you didn't see this comming?

Best Regards,
Bill

[jeff jackson]

Hi Chaps,
I thought that I would stir some debate on this subject. If I had an infinite budget, I would be able to add loads of goodies to the car, pay someone to spend weeks fiddling with jets on a rolling road etc.. etc.. But, and it's a big but, I have very limited funds. I try to save money and then when I have saved enough, I spend it on the car. ( Much to my wife's annoyance).
I have just bought some 45 idle jets from Eurocarb, on their advice, and again they seem to be following the line that it's the exhaust that is not supplying enough back pressure. ?20 for the jets so I'm going to try this.
It may be a bit Heath Robinson, but I have to get the car running a lot leaner than it is at the moment. It's a start!!

Thanks as always for the replies, very interesting reading.
Kind regards
Jeff 72+2

[garyeanderson]

Hi Jeff

I guess if you want some help from the folks on the forum you need to answer some of the questions Bill and myself and others have asked. Fuel economy mostly comes down to how you drive (binary throttle) and tire pressure and wheel alinement. Weight has a lot to do with it also, if you are in stop and go traffic all the time. Idle jets and low back pressure do not explain 10 to 15 mpg when others are getting 30 to 40. A tight engine may also be an issue. When the engine was rebuilt did you measure the amout of torque it took to rotate the crank, the crank shoud spin freely by hand and if you spin it it should continue for several revolutions. With the rods and pistons 7 ft/lbs would be an excilent number, something like every additional ft/lb costs 1 hp at high rpm. If it were me, I would pump an extra 5 psi into all 4 tires and see what your milage did, if the ride suffered measurably I would back it off some, if not and you got an improvement I would increase the tire presure some more up to around 35 or what ever the stated max psi stated on the tires sidewall. The air presure costs you a trip the the gas station and it sounds like you have been visiting it a lot lately anyway.

Gary

[rgh0]

Have a look at yahoo group "sidedraftcentral" they have been doing some interesting work on mileage in recent times. Playing with vacuum advance and variety of mods to idle and main jet circuits in quest for good cruise mileage without loss of max power

cheers
Rohan

[andyelan]

OK Bill you asked for it.

Comparison between 1973 Elan Plus 2 130S/5 and 1974 Europa Special
Both UK spec. Big valve TC Engine. Both standard with no modifications

Europa Spec.
Weight 712Kg
Tyres 175/70x13 front 185/70x13 rear
Pressures 18psi front 28psi rear
Top speed 123mph
Gearing
(overall)
5th 3.289:1
4th 4.574:1
3rd 6.086:1
2nd 8.807:1
1st 13.646:1

Carbs. DHLA40E
Main Jets 135
M. Air corr 200
Idle Jet 47
Idle jet holder 7850.4(160)
Pump Jet 33
Emulsion tube 7772.5

Fuel consumption 35-38mpg

Elan Plus 2 Spec.
Weight 876Kg
Tyres 165x13
Pressures 20psi front 24psi rear
Top speed 121mph
Gearing
(overall)
5th 3.016:1
4th 3.777:1
3rd 5.165:1
2nd 7.578:1
1st 12.064:1

Carbs. DHLA40
Main Jets 120
M. Air corr 130
Idle Jet 50.2
Idle jet holder 7850.2(120)
Pump Jet 35 ( was 45 Change made no noticale difference )
Emulsion tube 7772.5

Fuel consumption 26mpg

As regards to drag, I assume as top speeds for both cars is similar, overall drag will be about the same. Cd for Plus 2 is probebly a bit better but against this is the Europas smaller frontal area.

The biggest difference is of course weight, 164Kg more for Plus 2 over the Europa. That's certainly is noticable when driving

Anyway that should be enough to keep everyone talking for a little while so I'd better get this posted now before I loose it

Andy

[bill308]

Great info Andy.

Do you do mostly high speed driving with your cars or is it mainly around town driving?

Would you say you have a lead foot on the accellerator or are you always trying to eek out best milage?

I'm just trying to get an idea as to which driving range is most important to your style of driving and under what conditions these milage figures were recorded.

Bill

[bill308]

Andy,

A couple of other bits of information would be helpful.

Choke sizes?

Ignition advance specs including initial advance and advance curves (i.e. advance verses rpm), plus total advance, all in crankshaft degrees, same?

Cams fitted, same?

Compression ratios, same?

Bill

[andyelan]

Hi Bill

I've owned the Europa for almost 25 years now, so I know almost everything there is to know about it, however, I only got the Plus 2 about 10 month ago so here I'm still on a bit of a learnig curve. I'm finding it very interesting how similar and yet how different the two cars are.

As neither car is used for every day transport they tend to be used out on open roads rather than in town and although I wouldn't say I have a lead foot, I do drive in a reasonably spirited manner, they are after all sports cars. I do probebly drive the Europa a bit harder than the Plus 2.

One thing I have found is that the Plus 2 fuel consumption seems fairy insensitive to how the cars driven, I generally get around 25-26mpg no matter what. With the Europa however, although I normally get around 35mpg, this can improve to almost 40mpg with really steady driving.

Regarding the carbs, I think the Plus 2 is on 33mm chokes while the Europa is on 32mm. I dont know how the jetting for the Europa was arrived at (it not listed in any Lotus literature) but I do remember, years ago, I satisfied myself that this was most likley how the car left the factory, I just can't remember where I got the info from. I know I've never changed anything as the car runs very well as it is.

Both cars now run 23D4 41189 disributors (points ignition) which I set at about 10 degrees static advance, this I think gives about 25-26 degrees maximum. Originally the Europa had a 25D4 41225 distributor with a vacume retard module but I replaced that as it was worn. The retard module never seem to do much anyway.

Cams are the same in both cars ( D-type ) as is the compression ratio (10.3:1)

Hope this gives you a bit more food for thought

Andy