It may be connected with the frequency with which you post.

Location: Stoke Poges

The average of 40 mpg in my modern car was obtained the old fashioned way by recording fuel bought and mileage over the last year - I wanted to see what it was really doing - I expected better than this - it is a 1.4 petrol Golf automatic! Typically, the computer gives an average of about 42mpg for a journey, but less on very short runs and a bit more on the few long runs I do. So it seems about right.

Driving style can make a big difference to fuel consumption - gentle acceleration and changing up early, as per taxi drivers round here, no doubt helps - but it is hardly fun.

Obviously a Ruby won't do 60mph and 60 mpg at the same time - but how is 60 mpg achieved at all? At what speed is the optimum mpg obtained? About 30-35mph?
Colin

Location: North Cheshire

The secret to good mpg is always coast downhill! Brakes?, what brakes?!!
Less traffic on the roads in the sixties.

Location: Wales

My Ruby is doing about 38 mpg at the moment, but it is settling down after many, many years of inactivity, I hope that this will improve, but there are a lot of hills around here and the engine is using a lot of revs to climb up, I have an HC head to fit, so hoping to improve on the performance & mpg!

From my experience with my "modern", (1965 Rover P6), when I had my first example (1971 car) in the 1980's, running on nice 4-star leaded fuel, around town I would get 25mpg and, on long runs, I could get 37 mpg, now, around town it is more like 22 mpg and the best I have had on a run is 32 mpg - I seem to recall that on the introduction of unleaded fuel that mpg would increase by about 10%, which fits my figures for the Rover, so for the Ruby, perhaps it would have got about 42 mpg on full fat petrol!

Location: Saltdean, Brighton

I refer to an earlier thread on this board re. Fuel Consumption:

http://pub25.bravenet.com/forum/static/show.php?usernum=2099944454&frmid=5&msgid=924577&cmd=show

I have never achieved anything like 40 mpg, except for one memorable run from North Norfolk to Trowbridge, where we had a North Easterly gale on our tail in a SWB saloon and did 250 miles on the 5 gallon tank!

On a cold engine, a Seven struggles to do 20 mpg but this usually rises dramatically as the engine warms up. On modern fuels, an average mileage of 35 - 37 is what I usually measure, although my Chummy is currently turning in less than that (last measure was 33.5 on a run). No, I don't have a lead right foot but I do measure my fuel consumption (from tank top to tank top divided by the mileage driven) fairly accurately. My car is driven briskly and I try not to be a nuisance on the road, so cruise at 45 - 50mph, 50+ downhill.

35 - 37 mpg is my average over many different A7's (three Chummies, two Ruby Mk2's, RP Box, AH tourer, RM Box)over forty years.

BTW, my Big 7 Forlight is considerably worse as far as fuel consumption goes with 160 miles on 5 gals being the last recorded consumption. (32 mpg)

Location: North Wiltshire

Tim - now that we're getting away from Rubys, I looked up the other day the results of a Victorian Light Car Club Economy Test held in May 1926. A '24 Sports I own (determined to get it back on the road before end 2016) came only 2nd in the Members' Class with 78 mpg. Lest anyone thinks it was tuned to be gutless, this allegedly 50 mph Seven (claimed as such by the Factory) recorded a 58 mph lap at Aspendale circuit and a 63.2 mph lap at the Melbourne Motordrome, both in 1925. At the RACV Speed Tests at Laverton it won Class A Flying Mile at 66 mph in 1927. It (always unblown) also came second in class to Waite's blown Seven in the 1928 Australian Grand Prix. I'm sure I've seen better economy results with especially-detuned Chummys - does anyone know of top efforts? Hopefully they don't include the free-wheeling downhill efforts that I know occurred. Cheers, Bill in Oz

Location: Euroa

I must be a 'leadfoot' - don't think I have bettered 35 mpg in the Chummy or Sports (a bit tricky to calculate with litres and kilometres, but l per k doesn't mean a thing to me).

Maybe because these two have SU carburettors I push a bit too hard for economy.

I haven't checked the Saloon fuel consumption with standard light shaft and bronze updraught Zenith, but with the heavier body I don't expect much better.

Tony.

Location: Victoria, Australia.

In the mid 1920s the Austin agents ran a Seven chummy two occupants “non stop” Auckland to Wellington return 1000 miles and claimed 50 mpg. Roads would have been almost all unsealed with many miles in 2nd. May have coasted down grades. A similar 680 mile escapade in the SI but over even more arduous route, including river fords etc averaged 45 mpg.

The Brooklands publications repeat a 1938 Light Car account from a Seven owner who in 8 years had covered 80,000 miles over 5 second hand Sevens, including a magneto model. Average consumption dwindled from 44.5 mpg to 35.7 for the last and latest. (Incidentally only 1 pint oil per 400 average including changes!)

Around 1950 my father maintained very diligent checks on our stock RP. On recurrent 200 mile trips on the winding and undulating roads of the time, with 2 light adults and 2 small children repeatedly recorded 50 mpg. He originally drove at 45 mph but found this too fatiguing and settled for 40 mph. (Despite the most diligent maintenance, the car has never exhibited the stability now claimed for these cars).
Curiously, with a simple silencer with few baffles, mpg reduced to about 40.

Truly flat roads are very rare but on one the same car in my use would eventually reach 50 mph indicated; the speedo much more conservative than all it was compared with so probably accurate. With later head and SU and slight cam mods, with moderate assistance from wind or grade showed 60 mph. In this state, driven hard everywhere, no experiment for greater economy, checked over tens of thousands of miles, returned 38 mpg town or main road. A Ruby is lighter but better streamlined.

Power required is more closely related to the cube of (air) speed rather than the square.

The mpg from current fuels is debatable. I recently had cause to cover 1,000 miles of main road driving in a Jowett Javelin and this gave better than true 30 mpg, the mileage obtained 1970-1990 with such a car at the same speeds. The recent car had standard jets but raised c.r which would have assisted. No ethanol.

Someone may have access to data on the fuel relative heat values. Ethanol has a much reduced heat content and is a con.

Location: Auckland, NZ

After many years of thrashing around and breaking cranks I now rarely do more than 45 mph in my very late Opal which is standard other than a Phoenix crank and remote oil filter, standard carb. On a trip last year to the Loire it averaged over the 2000 miles 35 mpg, OK fully loaded as you would for two weeks away but I believe that some of the figures quoted are to say the least. EXAGERATED.
Whoa, happy new year

Location: Oakley ,Hants

The 48mpg consumption I attained was on a standard RN fitted with a Zenith T24. This car was my daily driver at Uni, covering around 60000 miles in 4 years.

I have never got near to matching this economy out of any other Seven and attribute it almost entirely to the type of carb.

I am sure that my RP was more economical before I fitted the late Ruby head and an SU carburettor. However it didn't go nearly as well! I guess with everything there's a trade off. I reckon I average about 35mpg these days which isn't bad given the terrain round here.

Location: Gard, France 30960

Ruairidh what jets are you using. I have never got anywhere near that with my 24Ts

Location: Farnham

David,

I cannot answer that - sorry. I stopped using the car in 1996 and it is now owned by a musician in York.

It always required full choke to start, however hot the engine was, had a terrible flat spot and is without a doubt the slowest Austin I have ever owned. It chewed clutch toggles, which I put down to Glasgow traffic, but was a total workhorse.

I have 24T2 settings in my note book as follows, could not tell you mpg attained.

Choke 14mm
Main jet 75
Slow 50
Air bleed 150
Needle & seat 2.0

Location: Auckland NZ

With the 22FZb our RNs average 35 mpg and I usually reckon on filling up 3 gallons every 100 miles, I don't fill the tank to the brim about 4 1/2 gallons so that gives me 1.5 gallons up my sleeve. However on the run back from Falmouth initially I was doing 50 mph on full throttle, but after about quarter of an hour I was having to back off the throttle to keep down to 50 mph. I filled up at Exeter services and tightened up the hand throttle friction clamp and cruised up the M5 at 50 mph. After 130 miles I thought I'd better fill up at Strensham services to find I could barely get 2.5 gallons in which gives about 50 mpg at 50 mph. It was a blisteringly hot sunny day, when Sevens seem to go well