So the T2 is a fair bit less draggy and weighty than the T3, makes sense... we have some drag figures for T3 somewhere. Think KTRev posted them a while back. Not so sure about T2 figures though, maybe somewhere on t'Internet?
Imperial gallon = 4.546
yes, that'll be 4.54545 recurring then. I find 0.22 is easier to remember and dead accurate. A bit like 3.2808398.... feet in a metre, 0.3048 metres/foot is dead accurate and not recurring.
Optimising the speed and throttle setting for maximum economy has always been a big discussion point in motoring circles, particularly amongst competitors for economy trials. And its well known that throttled Ottos are thermally inefficient due to pumping as well as friction losses, going against the grain of normal reasoning. Here is an example of a fairly typical, modern and efficient injected engine. These are SFC curves developed by cross-plotting the manufacturer's SFC mapping at various throttle settings
The first thing to notice is that the engine is using about 2/3 of the fuel flow
per HP when at full throttle(120 lb-ft) than when at low throttle (30 lb-ft)
Then, that this is potentially a 'good' engine across the board, as the curves are quite flat over a broad range...
Then, that 4,000 rpm would be the max. cruising revs as sfc definitely starts to climb seriously beyond that, unless at full bore.
The yellow and light blue lines look worthy of study, 45 to 50 lb-ft, and the rpm band 2500 to 3500... as this might represent the nominal torque to cruise at a normal 'traffic' speed. Note at lower torques, even 5 lb-ft less, the purple curve is showing a fairly big jump in sfc (+10% @ 3000 rpm).
But to determine the
optimum , best mpg, one would have to cross-plot these curves, yet again, with the full drag polars for the vehicle in question and this would then tell you what gearing is required (if top gear was the one you wanted to cruise in) to achieve that 'best' mpg...
You've said above, that pretty well the less throttle you use and the slower you go the better the mpg...
I think the latter is generally the case, but not necessarily the former (which we know from economy trials around closed circuits, very small engines at full throttle, sometimes being used in 'burst and coast-down' mode)
Without doing the cross-plot, there would be a minimum speed as well as a minmum throttle opening. My guess is that this minimum would be too low for practicality 30~ 40 mph at a guess), but that an 'optimum' could be found where there was very little increase in consumption for a significant (say 10 mph) increase in speed...
Another conclusion, pretty self-evident, is that the lower the combined rolling and aero drag, the higher the max mpg speed would be, and an optimum point commensurately higher still (we know a small low-drag modern saloon doesn't suffer terribly when going from 50 to 70 cruising speed)
NB. Weight affects rolling resistance, not insignifcantly, but only to the first order.
Food for thought...
Sold it to a mate for his baja bug with 85k on it and he put another 22k on before he threw a rod. I told him when he bought it to replace the bearings and rings, but he didn't.
