Originally Posted by renault_megane_dci
Since most cars using the Atkinson cycle have cam phasers, the switch from Otto'ish to Atkinson'ish depending on power requirement.
A true Atkinson engine does not switch to the "Otto'ish" cycle when more power is required. Doing so would create holes in pistons due to the higher than Otto compression ratio. They do vary intake valve timing at various speeds and loads, but only a small amount.
Atkinson engines (in the modern sense) require:
1. Increased static compression ratio
2. Deliberate reduced volumetric efficiency via delayed intake valve closing
If one of these is missing, it is not an Atkinson cycle.
1. Increasing static compression ratio without delaying intake valve closing will make things go bang (in a bad way).
2. Delaying intake valve closing without increasing static compression ratio will decrease pumping losses slightly and increase efficiency slightly, but not nearly as much as with a true Atkinson cycle.
In order to make your motorcycle an Atkinson engine, you must raise your compression ratio. You must also ensure that you have reduced the volumetric efficiency enough that dynamic compression will not even get near static compression ratio and ruin your engine.
IMHO, creating a VVT system is pointless...an unnecessary complication. For your purposes:
1. Compression: plane the head [like crazy] and install a thinner head gasket (if available). Measure combustion chamber volume before and after. Static compression ratio = (swept volume + combustion chamber volume) / swept volume.
2. Intake valve timing: weld and grind the intake camshaft lobes for delayed valve closing. Install a degree wheel on the crankshaft and dial indicator on each intake valve as you weld and cut and grind each lobe.
3. Write everything down.