Originally Posted by joejack951
I've never done any scientific tests to prove it but if you don't have enough heat to completely burn a fuel, then your economy should go down. By cylinder temperature, I'm referring to the same thing as you are with combustion chamber temperature (and I would have said the same thing had I been thinking more when I was typing
). I was talking about pump gas and thinking along the lines of running 93 octane in a car meant to take 87 octane (and not just one that can run on 87 with a knock sensor).
Maybe "completely burn" isn't the right way to look at it. When the piston is at it's top most point (or at whatever point the designer's set to have the spark plug fire), the engine was designed around the fuel being ignited and burning at that moment. With a cooler engine, I would think the fuel would at least burn slower than in a hotter engine. This slow burn would cause a loss in power.
There's never a shortage of heat when it comes to combustion chambers, with the exception of a car that hasn't warmed up to operating temperatures yet. Getting all the fuel mixture to burn is a function of design. You need the proper mixture from a carb or fuel injection system, and correct intake port length and size for optimum velocity. You also need correct valve lift and timing, along with correct ignition timing. That mixture has to be in the chamber with the valves closed at the right time for peak performance. I don't think pump gas can burn too slow in a production car. If you want to learn more about great designs, look at Ducati's Desmodromic valve system.