Quote:
Originally Posted by ksa8907
I wish you the best of luck.
Pumping losses are directly attributed to high vacuum. Which is why diesels have low pumping losses.
Most high efficiency engines/hybrids use a cam profile or cam phasing to achieve late intake valve closing. This gives lower dynamic compression ratio but increases the expansion ratio.
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Diesels have "low vacuum" because they use turbos to fill the vacuum. By their nature they must open the valves late so that they don't hit the pistons. If they were naturally aspirated they would create lots of vacuum. The turbo is there to help fill the cylinders because of their limited lift duration.
if what you're saying were correct, then I should use a lopey cam and expect better mpg. the truth of the matter is engines need vacuum to run properly. If the intake valve opens too early you get lots of misfire. Vacuum creates the air speed that entrains, atomizes and emulsifies the air/fuel mixture, which creates a faster burn. A Toyota engineer gave me the Prius cam specs (which was at 40% BTE at the time). They phase the cam so that it closes at 100* ABDC, which means it opens the valve much later than typical...which means lots of vacuum. They give up a little pumping loss for better combustion and a much lower compression ratio (negative work).
I'm replacing broken sensors and fixing air leaks atm. My lean burn baseline should be around 40mpg...it's after that that I may need a little luck
