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