12A Pports can do 310 HP at 10,700 RPM at
.667 .
Lynn E. Hanover
Thanks for that Data point, Lynn. I see if I can use it to get a
gestimate on PP Ve.
So if a 12A is 73 cubic inches then
at 10700 rpm and 100%Ve it would flow
73*10700/(1728) = 452 CFM air flow.
So if at this 100% Ve we get less power than 310HP then
we can assume the Ve of the 12A must be greater than 100%Ve to give us more
power.
At sea level standard day 1 cubic foot of air = 0.076 lbms. So for
that flow we would have 0.076 * 452 = 34.35 lbs/min. Now I
don't have any idea what Air Fuel ratio a rotary racer uses but I best power
is reportedly to close to 12:1
Assuming a race air fuel ratio of around 12:1 then the fuel needed
for that ratio at that airflow. Then the fuel needed would be
34.35 /12 := 2.8624 lb of gasoline per minute.
A lb of gasoline has 19000 BTU depending on
octane. Higher octane has less so assuming 19000 BTU/Lbm
gasoline, we can next calculate the power being produced in the engine.
Converting 2.8624lb/min of gasoline into lb/sec we have 2.8624/60 =
0.047708 lb/sec.
To find the BTU we have .048*19000 = 912 BTU/sec. IF ALL this energy
were converted to torque it would give 912 *778 = 709536 ft-lbs of
torque. or divide by 550 = 1290 HP!!!
Unfortunately, we know approx 50% goes out the tail pipe as heat and
another 25% (more or less) is Waste heat rejected by our coolers leaving us
somewhere around 25-30% depending on whose estimate you use
for efficiency of a rotary engine of 1290 *.25 = 322 HP
or using 30% 1290 *.30 = 387 HP
Hummm, since the 12A PP is producing 310, but the calculations
shows it should be getting closer to 322 HP that would suggest a PP port 12A
flows less than 100% Ve. If fact, it would suggest that the Ve of the
12A at 10700 rpm is closer to 310/322 *100 = 96.27%Ve.
But, this is instantaneous BHP, I have not subtracted for
mechanical or other inefficiencies so taking a guess that amounts to
around 5% of the total. Then to get a dyno of 310 HP the
engine would need to produce 310*1.05 = 325 HP. So here we would get
325/322 = 101% Ve for the 12A at 10700 rpm.
Given we know that some racers are restricted by the size of the
intakes permitted (is this true for the PP, Lynn?) perhaps that is why the VE
seems a bit on the low side. But, that's just a guess. Well, that
was my best crack at trying to determine the efficiency of a PP.
So anybody else having an idea or source of information or opinion - jump
in.
Ed