Just finished installing a auxiliary vacuum reservoir today.
While this won't improve my mileage any, I think it is well worth doing for safety reasons. Now that I am doing more EOC (mostly in heavy traffic) I have been concerned about only having a couple of brake applications before I lose my brakes. It hasn't been an issue yet but it could be. Took my lead from the EV conversion guys. Picked up a old 4 lb. fire extinguisher bottle from a extinguisher service company. They gave me a 5 lb. for free from the scrape bin. Finding a fitting was a bit difficult for this bottle as it was a odd size. Had to do some searching for an extra vacuum check valve but finally found one. Honda's made in the 90's use a hose mounted valve. Hardest part of the install was figuring out where to mount it in. Only did a quick check after install but looks like I now have 4-5 brake applications instead of 2 so I'm happy. Cost was $18 which includes a couple of fittings I bought and didn't need.
Looks like the kill switch is helping as well. Won't need to gas up for a bit yet but the gas gauge and the Scanguage are looking better. I'm getting to use this car in place of my Rondo quite a bit as well so saving even more fuel.
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Almost all my driving is done 1-5 miles at a time.
Best short trip: 2.4 l/100 km, 3.9 km