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I've been hypermiling my old Saab for some years now and have reached absolutely magic numbers I first found hard to believe. I roughly HALVED what is a normal fuel consumption for this type of car! First step was to reduce travelling speed a bit, then try to plan my driving to minimise the use of braking (engine braking included). This did gave some improvement.
Then I started to experiment with larger wheels, since the car has a 4-speed transmission with quite high revs on top gear. I also increased the tire pressure. I could clearly see a tiny improvement from this, but what really changed the game was to introduce "Burn & glide" driving in continous cycles of acceleration with almost full throttle, followed by coasting. When I started doing this the fuel consumtion decreased way more than by anything else, and I could not even see any difference from changing wheels or tire pressure.
The final very rewarding step was to introduce engine shut-down while coasting. This is just as extreme as it is rewarding! Fuel consumption made a huge dive again. An average burn & glide cycle has 15 20 seconds acceleration followed by 30-40 seconds of coasting with the engine shut off. Driving this crazy way is a lot of work, but you definitely get something back! :-)
I have installed two push-buttons on the gear stick and two relays. One button kills the engine by switches off the ignition. One of the relays "stick" in this position until the other button is pushed, together with the activation of the starter. I have a good engine that most times start in just one piston stroke so the load on the battery is not too heavy.
Note: I have a +40 year old carburetted car with no electronics what so ever. This makes starting and stopping easier/quicker than with some modern "electronic" engines that must rotate at least a full turn or two before finding the actual position of the pistons and camshaft. I have no air conditioning and no power steering. I do have a vaccuum servo for the brakes and that can sometimes be a problem or an unpleasant surprise.
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