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Nah, it's not the reduced knock margin. It is a direct mechanical effect of having to initiate the combustion earlier, while the piston is still rising, which starts to exert combustion pressure on the rising piston earlier, making the rest of the engine work harder to finish driving the piston up to TDC where the combustion pressure stops being a negative and starts being a positive. Your modern engine that only needs ~10° to make MBT doesn't waste the other 10 or so degrees of crank rotation. That's almost all of it. The difference in knock margin might go either way. Remember that modern engines to which you are currently comparing the long tractor engine (the RB) are now running super high compression, direct injection, tricky cam control and maybe even cylinder pressure sensors. You're not comparing apples with other fruit. It's apples and sea weed, or some other evolutionarily primitive vegetation. And remember, squish only really comes into play at the very end of the stroke. It certainly does good things, but it is not the biggest contributor to what's going on. It is quite possibly much less important in 4 valve head than 2 valvers also, because there is so much less squish available to a 4 valve anyway. -
By Dose Pipe Sutututu · Posted
Food for thought, a longer stroke motor would need less ignition timing vs. a shorter stroke motor requiring more ignition timing. -
Thanks Duncan, HART is only 10 mins from me (I did my bike license there), it'd be awesome if it ran these types of things. Sutton Road does look good and they take fewer cars than SMSP which is good. Surely you have enough land to lay a few million tonnes of concrete and some sprinklers D? -
By joshuaho96 · Posted
I thought an engine that needs more ignition timing to make power is going to result in less power due to reduced knock margin? More time for the combustion to propagate -> more time for it to heat up the rest of the mix to detonation. -
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