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Originally Posted by Paulgw
QUOTE:- I have to say that I was exceptionally disappointed when I learned that the Atkinson-Cycle engines used by both Toyota and Ford (Escape Hybrid) were not true Atkinson-Cycle in that they still have 4 distinct cycles and it takes two full revolutions of the crankshaft to complete one power cycle.
The True Atkinson Cycle engine takes 1 full revolution to accomplish all 4 strokes via it's linkage and intermediate shaft (a marvelous design).
The Engines we are dealing with here are (for all intents and purposes) standard Otto Cycle 4 stroke engines that have a special valve timing mechanism (VVT). I truly have no idea at this point how either Toyota or Ford can claim Atkinson-Cycle engine..
Probably the "modified" Atkinson-Cycle (I think this is what I've heard this design called), engine that Toyota produce has the advantage of simplicity and less moving parts to wear out.
I assume it would be possible to boost the output of the engine by closing the intake valves sooner thus upping the effective compression ratio on the combustion stroke to the maximum that premium fuel could tolerate? I'm not suggesting anyone try this it's just a hypothetical question.
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I agree that it would be a Modified Atkinson Cycle engine - I just wish Toyota and Ford would call it what it really is...
In regard to maximum compression ration on premium fuel - I can speak to that one but not with the TCH. I've done a lot of work in the field of auto-racing and engine design / building. The highest compression ratio you can typically get by with in a non-ECU controlled vehicle is 10.5:1 with alloy cylinder heads and 92 Octane fuel.
Some other points of reference:
I've got a 69 Camaro-SS with 10:1 with Iron Heads and have had to reduce the timing substantially in addition to not lugging the engine in any one gear or detonation occurs.
I've also got a 70 Nova Pro-Street car with a 468 Cubic Inch Big-Block that has 12.5:1 compression. It requires 100 Octane minimum for its 605HP. I'm in the process of building a new 468 inch engine for the Nova that will have a static compression ratio of 9:1, but the GMC 6-71 Supercharger will raise that effective (dynamic) compression ratio to between 13-15:1 depending on the speed of the blower. It will be running on E85 rather than gasoline.