as far as engine design goes , GDI is great , the 2 , 4, 6 , 8 concept ( used in GM trucks ) is smart . Heres the nuts of it . The 4 stroke has so much parasitic drag due to the valve train . back in the 40's , a new engine design was called the sleeve valve engine . It was a 4 stroke , but had sleeves that rotated in their bores that would line up intake and exhaust ports like a 2 stroke , BUT the timing was controlled by a camshaft . I used to know a machinist that had worked on them and been around them and he said they were so quiet you could stand next to it and have a conversation and never know it was running , so more efficient because it wasn't having to compress valve springs every stroke etc . BMW had a Europe only 2 series that had a solenoid driven valve train ( kinda like F1 cars ) . Its biggest downfall was the electrical energy required to run the solenoids at high rpm. standard automotive alternators couldn't produce enough voltage to drive the solenoids . A modern sleeve valve engine with GDI would out perform anything on the market , mileage would be through the roof and yeah oil companies probably wouldn't be really enthusiastic about it . The same machinist I knew ( his name was Gaines Markley , feel free to google him , he was a bad ass dude )
years ago had a idea for a Rotary Screw Valve motor , long cam like rollers with " valve ports " were engineered to create a high power , low drag engine that would put poppet valves to shame , they made prototypes , but obviously it was never a production engine , otherwise we'd all know about it . They key to a efficient , powerfull internal combustion engine , is combine the low end power a 4 stroke produces , with the high rpm freewheel of a 2 stroke . Honda did just that by inventing VTEC , they did it by using multiple cam profiles that made a " wider " powerband ( yup , our beloved powerband ) . Honda Invented VTEC in Formula 1 to make their v6's run with the v8's .
anyways , its fun to think about it .
