1915 Indian 8 valve Vtwin with a strange exhaust system. What's up with this?
[video]http://www.youtube.com/watch?v=TfEZyCccKTs&list=FLVH7O3Ca2Fi5wCX2fHszypQ&index=20[/video]
For many decades after the birth of the internal combustion engine, it was held that getting the burnt exhaust gases OUT of the cylinder was the limiting factor in good combustion - and getting more rpm and more speed out of an engine.
In the teens, you see those "cylinder ported" engines spitting fire and flames out of such drillings - race engines had them around the exhaust port AND also around the base of the piston travel. They spat enough fire that the riders had to wear asbestos wrappings on their knees and ankles. They simply made the incoming charge rich enough that it spat the excess out the ports, and sucked air to make it all burnable - and had an adjustable main jet to tweak it all while on the fly. Oval dirt track racing in the USA in the teens had many such racers - Indian Harley Excelsior Cyclone Flying Merkel - and in ohc, ohv, sidevalve you name it they did it.
So you have the "Big Valve Excelsior" of 1912, that 1st did a +100 mph lap of a small dirt oval.
But it was the exhaust valve that was dinner plate size (almost !).
If you make everything big enough, its bound to do OK....
It wasn't until the 1950s really that it occurred to folks that the INLET valve needed to be bigger, to get more inlet charge in.
And the exhaust gases, under a fair old pressure could make their own exit without any assistance.
Now, JAP in the early 1920s did a neat little OHC single - with a fair sized exhaust valve.
Stanley Greening, JAP engine man commented that in the 1950s they tried the little ohc with the ports turned around, and with a big inlet valve it now revved to 8000+ rpm, and made prodigious power..Amazing what 30 years of accumulated thought and development can show. - if only they'd figured it out a century earlier ??
Opethishelps.