Originally Posted by
markk
Fuel or fuelling ?
The fuel, ie what petrol they are using.
Also having the rod at TDC (or around the cylinder filling point) gives a greater opportunity and timing scale to fill the cylinder at any given revs.
The "cylinder filling point" is much lower down the stroke, more like 90 degrees, rod length has little effect there, however what does happen is that when it hangs around at TDC it wastes time that the cylinder could be getting filled, but then conversely you see a greater pressure differential when it does start moving, but that entirely depends on the valve timing as to which of the 2 effects is better, so very difficult to make any sort of generalisation about.
Why would the YB have the shortest rod then ? because its the oldest engine design !
I cant think of any engine that uses rods that short anymore, the crank stoke on the YB is relatively short, hence why a decent specced YB will love to rev, add into that longer rods and you are heading into a territory that also elongates your engines life expectancy.
Agreed the rod ratio is suitable for an 8v transit van engine, but thats what the geometry was designed for, the YB wasnt designed to be a performance engine, it was a modified version of a very much non performance orientated one.