“Heck, stations even used to give away free items (such as drinking glasses) to attract customers.”
I know that this sounds bizarre, but it is true.
Back in 1961, when my brother started college, he used to gas-up his '54 Ford at a cut-rate gas station enroute to the college. Did that cut-rate station give away drinking glasses or dinner plates, or something of that ilk? Nope! They gave their customers one roll of toilet paper for each fill-up.
A year of so later, that same station began to give away a small bag of traction grit with each fill-up during the winter months. Most likely, the traction grit was even cheaper than toilet paper. Personally, I thought that the traction grit giveaway was a great idea, and both of our cars had a supply of this stuff in the trunk for several years until it was used-up.
Some cars back then used rolls of TP as the oil filter. Universally consumable item but also applicable to some for their car!
I changed a toilet paper filter in a GMC Carry-All. Had to unroll some of the toilet paper to get it to squeeze into the holder.
Amazing howell it cleaned the oil!
Still available to day?
This idea was tried in 1935. The Pogue ( or Fish) carburetor.
If you are looking for efficiency research the Atkinson Cycle engine. The Prius uses it. Or think about turbo charging to recover waste heat. Just remember the intercoolers waste some of the recovered waste heat.
Years ago, Smoky Yunick modified a Plymouth Horizon so it delivered 50+MPG…Popular Mechanics magazine sponsored the effort…The project was a success, the basic technique used was to eliminate as much waste heat as possible by recycling it back into the engine. Engine operating temperature was raised to 300 degrees or so by using coolant and materials that could withstand that heat…
http://www.hotrod.com/techarticles/engine/hrdp_1009_what_ever_happened_to_smokeys_hot_vapor_engine/viewall.html
There’s a conspiracy theory that pressurizing gasoline into fumes before entering the combustion chamber would result in a 5-fold increase in fuel efficiency. Tom Ogle was the alleged inventor of this system. Read here for more stories and debunking of this theory.