Suzuki Vitara 1997 5 door with Mazda 2ltr turbo diesel

[ted frater]

Yesterday, i had the first opportunity to do a motorway trip, ie constant speed cruising,since starting to mod this car for economy.
I did a total of 140 miles with 30 of those in urban stop start mode.
The tank was brimmed at home and refuelled at my nearest diesel pump on my return.
total fuel used was 14 ltrs, or 3 imp gallons. This gave me 46mpg cruising at 50 to 55 mph.
This is with the car in standard mode with 185 by 75 by 16in 8ply rated tyres running at 40 psi.
I do all the hypermiling things , like coasting, no braking unless I need to, gentle accelleration etc.
so im more than pleased with this result for a 80,000mile 13 yr old diesel car.
Its used no oil in the past 3000 miles and the oil is still transparent. largely because ive blanked off the exhaust gas recirculation pipe.
What im after is 50mpg at 50mph.
Well be working on that.
as anaside, ive tried running on bio diesel, but the engine does prefer ordinary diesel fuel, on which its more economical. Dont know why at present, guess its to do with the slower burning rate of bio fuel.
The next test isto fit a boost gauge to see if and when the turbo starts to work ,if atall at a steady state speed of 55mph.
wether increasing speed to 60 and running on boost gives better economy, well have to see.
My guess is that one should run the engine at the peak of the torque curve as ofter as possible.
any suggestions?
Ted
Down in Dorset in UK.