I was reading on an aircraft forum last night that the p-port rotary
doesn't make much power below 5000rpm, how accurate is this? if so does
this mean economy cruise is difficult to achieve? My airplane spec calls
for 160-210hp, so that is about 135hp for cruise. With a p port at 250hp
I would have great speed from the extra hp at altitude at WOT and i can
just limit manifold pressure in the lower levels to 210hp to prevent the
engine departing and taking the firewall with it. Maybe the compromise
is with the length of the intake runners? Is it really possible to have
the best of both worlds here or do I need a reality check?

Alex

I depends on the intake runner length. Make it 24 inches and that will move the best BSFC point down the RPM range. You will lose a bit of power at 7500 RPM but your cruise prop may prevent that max RPM anyway.
I assume a fixed pitch prop. If you want the best of all worlds use a variable pitch prop and a trombone intake manifold like the Le Mans engine had.

Pau Lamar

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