Most V8s use .5 gph idling. I told my neighbor my 2002 Insight CVT would go 40 MPH on the same amount of fuel his V8 chevy truck used idling (.5gph). To get to 50 MPG, your car would have to idle, without any increase in fuel burned while moving at 25 mph, with exactly the same amount of fuel it used idling.
My Insight used .11 gph idling, just over 20 % of a V8s consumption and the Insight was a very aerodynamic car with a cd of about .25.
Without some very serious aero modifications your goal is virtually impossible.
The work you have done on the combustion chamber is fantastic and a tribute to your capabilities, but by eliminating the aero factor your enegy consumption will not be reduced driving the car at any speed above 25-30mph.
That being said it still is possible that your modifications could help to improve mpg, but think of it like this, manufacturers spend billions on improving efficiency. You would have to achieve thermodynamic efficiencies approaching 55% which is the best ever achieved with very large diesel engines such as those that drive the largest container ships on the planet, running at less than 100 rpm, with a 3 foot bore diameter and a 9 foot stroke.
http://en.wikipedia.org/wiki/Brake_s...el_consumption
Can you get 50 mpg, within the limitations you have imposed (no aero improvements)? It's possible, but only if you use engine off P&G at average speeds of about 25-30mph.
regards
mech