spacer wrote:Be carefull with the "the bigger the bore the better" line of thought, there are limits to the advantages of a wider bore / shorter stroke.
Current F1 bore/stroke are probably dictated by engine speed (the high reciprocating forces and need for ultra wide valves to allow some useable volumetric efficiency being the problems).
The large bore / short stroke has disadvantages in terms of mixture burn; the wider the bore the more crankshaft duration one needs to burn the mixture, with fuel burning speeds as a given for a certain set of engine operation parameters, this forces more ignition advance and thus more pumping losses and stress put on piston/rod.
Another big disadvantage is the actual space that's available inside the combustion chamber - piston to valve clearance being important. This both limits the cam lift and geometric compression ratio. I'm quite positive current F1 engines run at CR's much lower than the engineers would ideally like to with the current fuel specs.
Let's agree that current B:S ratio around 2.5 is interesting and unprecedented (and I do agree with some of the above)
surely VE is unprecedentedly high around 120%
larger B:S ratios automatically tend to ample valve area
(with B:S rise valve area rises faster than demand on valving via rpm rise)
we have had special fast combustion fuel for 20 years in F1 (ign advance is not abnormal)
if combustion speed was a problem we would have twin spark plugs
so pumping is not abnormal (the stress described is in principle helpful)
CR is nominally around 14
current fuel spec (right now) has no max octane limit (interestingly)
high octane may not be needed anyway
(if spark-initiated combustion outstrips the (delay) time for detonation to start, there is no detonation problem, 1960s Honda GP winning motorcycles needed only 65 octane around peak power rpm for this reason (granted only 44mm bore))
(diesel has a delay time, so does petrol)
sometimes I can't believe how well (brilliantly) F1 engines do their special job !