New intake and exhaust manifolds, a variable induction system for air intake control, equal length exhaust pipes coupled with a muffler off the high-performance Skyline GT-R ( a muffler flap valve opens at 2, 000-2, 400 rpms and cuts exhaust system back pressure ), and platinum-tipped spark plugs good for 100, 000 miles.
22.
In fact there were two flap valves in Joseph Day's original design, one in the inlet port, where you would probably find a reed valve on a modern two stroke, and one in the crown of the piston, because he did not come up with the idea of the transfer ports until a couple of years later.
