Ron B.
F4Fguy
Lou:
Some say tomatoe,some say tomahto.In this as in other things the model community has it's own language.Like tail moment being from flap line to elevator line,or pipe length from center of the cylinder to the first baffle.In all the literature I have on two stroke cycle engines,the blowdown is the period in the exhaust/power stroke between when the exhaust first opens,and the intake first opens.
On the intake/compression stroke intake closing leads the exhaust closing,since by definition,both the intake and exhaust period are symmetrical.The reason torque is improved at lower RPM is that there's less mixture lost at low speeds,due to the exhaust timing.For a given timing,low revs give ample time to evacuate the cylinder.At higher revs the cylinder can't get the exhaust gasses fully scavenged,cylinder pressures equilibrate before the intake is fully closed and a lot of dilution occurs between exhaust and intake.This is the rev limiter.
I know I'm being pedantic here.It really doesn't matter what you call it,as long as you know the effects.In an ideal world,the exhaust would lead the intake in both directions.Since we're dealing with cylinder ports and are stuck with symmetry,there's no way to accomplish this (in a single cylinder engine).
What you're doing to the Fox .35 works well because the exhaust timing is very conservative.In a more "highly timed" engine you almost always have to drop the sleeve or otherwise retard the exhaust in addition to raising the intake.Sub piston induction is the usual limiting factor.
The thing we're really doing is changing the time/area.For low end torque and broad range the exh.time/area sould be minumum,and int.time/area should be as great as possible while maintaining enough blowdown to gain some inertia in the exh. gasses. Reverse flow into the intakes is the limiter here.