good video to explain octane http://www.youtube.com/watch?v=D9nhXNarFdg
Nice. Unless you change the compression ratio you'll not notice a difference with higher octane. So if I've got this right the variable cam timing will adjust the compression ratio and the variable cam height will adjust the mixture (guessing that second part?) so the ECU can make use of the higher octane to reduce the amount of fuel needed and increase the mpg? Not sure how the ECU will know how to do this though. Anyone confirm/deny this?
Variable valve timing has nothing to do with compression ratio. Valve timing is when the valves open in relation to the piston position, Compression ratio is the difference between the volume of the cylinder at bottom dead centre compared to top dead centre. They will not effect each other.
I always use Morrison's diesel and never have a problem with it. If you think there is a difference you are kidding yourself.
Save some money and buy the cheapest fuel it all comes from the same place.
Does the spark not come later in VVT then?
Erm, we are talking Diesel engines. There is no spark. the fuel combusts when it is injected into the cylinder under extreme pressure.
You are thinking about petrol engines. The timing of the spark is unrelated to the valve timing.
Compression Ratio: The difference between the volume of the cylinder when the piston is at the bottom compared to at the top. (cannot be adjusted without changing the crankshaft or changing the bore of the cylinders)
Valve timing: When the valve opens in relation to the position of the piston. (Not really adjustable you can change the camshaft or slip a tooth on the cam belt, VVT engines do change the valve timing in operation.)
Ignition timing(petrol engines only): When the spark plug sparks in relation to the position of the piston. this can be adjusted by moving the Distributor (on old engines) or the ECU takes control on modern engines.
All of these things are unrelated but need to be working in unison for the engine to run like a dream.
