woo-hoo! that worked, I simply changed from gallons to litres, I thought my previous fills would go haywire but they seem okay, and no my badge works, no data re-entry required!

Good news! Now you can add fuel ups and let fuelly do the maths, instead of you! ;)

https://badges.fuelly.com/images/sig-us/287118.png
Seems laptop might be fine, but mobile faulty? Pasted my badge in another topic and saw 51.6 again, despite figures on phone profile same now as on laptop...

https://badges.fuelly.com/images/sig-uk/287118.png
Correct badge success!

The guidance says you will not be able to get mpg for your first tank of gas (0 to xxx miles). But after that, the first odometer reading is stored, so subsequent odometer readings are used to calculate miles driven. If it is a new car the initial 1200 miles is the break-in period according to the owners manual, and the mileage will likely be lower than after a few hundred miles of break-in. I opted for using odometer readings since I would probably forget to reset the trip odometer.

Haven't registered my car yet, as it's far from standard. I suppose i just put in what it says on the logbook and go with that? It still looks like the same car, that's what i call it (though not what it's badged as).

With three times it's original power i'm not expecting the economy to be the same, although it doesn't seem to be far off. This is obviously a concern as i don't want to run lean and real-world journeys aren't reflecting the rolling road readings so.. i'm hoping this site will help me determine where my economy is at with various driving styles.

I'm lost... lol. What car/where are you having trouble?

MikeyMK,

Just register your vehicle and start tracking your fuel usage. There is a comment option so you can track what type of driving was don during a particular tank.

I'm intrigued as to what you are driving after your last post and also wondering why you would be concerned about fuel economy when you have trebled the power? This can only reduce your economy.

Anyway looking forward to seeing the stats for your car.

Oliver.

The car is a VW Polo Coupe S. It originally had a 1.3 8v engine with twin downdraught carb producing 60bhp in this spec (40-60bhp versions in the range).

This one has a 1.6 16v engine with individual bodies on it (quad carb), producing around 150bhp. The gearing is considerably longer (4.2-3.3 final drives).

My problem is that it's as economical as it was before. I get 100 miles to ten litres, so around 45mpg average, with varied driving. That's all very well, the problem is there's not much difference however i drive. Naturally it's not a car that can be pushed hard on the queen's highway for long, but throwing economy out the window and driving without a care for fuel, it still returns around 40mpg. The best i can get out of it probably isn't 60mpg.

This is a concern because i don't want to melt pistons running lean. I can account for some of it, over the original set up. Driving around town without exceeding 2krpm from the long-stroke engine, for example. My old engine would have to work hard just to keep up with this ticking over.. But i can't account for getting 55mpg teasing it, but still 35mpg opening the taps.

Clearly these figures are all very rounded, which is why i'm here.

I don't think carbs allow the fuel metering precision of fuel injection over different engine loads. You are relying on the speed of the air flow to draw fuel into the engine vs. having pressurized fuel being squirted in through the valves.

Under light load and low engine speed, the lower air speed in the carb with produce a weaker venturi effect. To avoid lean conditions from too little fuel being sucked in then, the carbs are likely tuned to run rich under those conditions. Negating to the potential fuel savings of light driving and low speeds. Once warmed up, fuel injected engines only run rich at full throttle for extra cylinder cooling.

As for non-stock cars, is there selection the user could make, to not have their particular car used for the model's database?