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Roy makes a very good point, something I’d not thought of. Can anybody state with any certainty how many core tubes these radiators originally carried and their size? Fin numbers, effectively surface area, would also have a significant bearing, anyone fancy counting ‘em?. With that information it would be a fairly simple matter to work out the rate at which the core might be expected to reject heat or at the very least do a numbers comparison with the current core.
One small point, I’ve tinkered on the test bed and elsewhere with a lot of different engines over the years and I can’t think of one that needed 35° of advance. I’m speaking of regular stuff now not racing machinery, that’s not my field. I’d have thought 28° to 30° for full advance would be quite enough for a 2stroke, which has a much lower effective compression ratio than the bore/stroke/combustion chamber volume might suggest. Too much advance will result in the pressure in the combustion chamber rising too early which will tend to slow the piston, in turn that will require more throttle for a given demand resulting in the engine burning more fuel and producing more waste heat. Something to consider maybe?
Mark you, too retarded can be even more embarrassing as evidenced by the Scott rider I met in Canterbury many years ago. I’d pulled up at the traffic lights by the cattle market; the Scott rider was going the other way. A smug grin crossed his face and while honour bound to wait for the green he was clearly anticipating thrashing my old Comet to the centre of the junction, which was the object of the exercise, and we both knew it. The lights changed, a big fistful of throttle and the confident grin changed in an instant to one of stark horror as he nipped smartly backwards and fell off! You’ve guessed it, he’d retarded the ignition to get maximum grunt and the Scott engine being at tickover had quite happily gone into reverses!
I even had the decency to stop as he picked himself out of the gutter and enquire if he was all right. His reply was unprintable even to this day . . .