People that know me frequently hear me say
automotive piston engines are not suitable for
use in aircraft. The long automotive life is based
on the fact they are not called on to generate very
much continuous power unlike an aircraft engine.

Of course the rotary is the exception to
the rule. It is hard to design a Wankel
engine that is not robust and long lasting.
One could probably build an e-shaft out of
aluminum and it might have enough life to use
in a car.

Here is the proof. This is a Dodge Caravan
of about 1994 vintage with a 210 HP engine.
I installed an aircraft manifold pressure gage
to show the actual HP being used to cruise the freeway.

As you pilots know the manifold pressure
and the RPM tell you the percentage of
max HP the engine is generating. The max power
the engine is capable of is wide open throttle,
29 inches of Hg manifold pressure and at the max
HP rated RPM. Probably in this case about 5500 RPM
as red line is 6000 RPM.

Tracy's entire EFI system is based on this relationship.

A crude approximation to the HP  generated is
given by the manifold pressure times the RPM. In
this case the indicated HP number is 20
inches of Hg times 2000 RPM or 40,000. Max HP
for this engine is probably  29 inches of Hg at 5500
RPM or 159,500 so this engine is making about
about 25% of the claimed 210 HP or 52 HP.

That ratio is 40,000/159,500.

Get a manifold pressure gage and install it in your
car and find out for your self.

As a double check the Dodge Caravan gets about 20 MPG.
At 60 MPH it is using 3 gallons an hour.
At 6.25 pounds per gallon that is 18.75 pounds
of fuel per hour. 18.75/52 HP is a BSFC of
.36. That is a bit low for a gasoline car engine so the
HP being generated is probably closer to 45 HP.
That would give a more realistic BSFC of around .42.

Bottom line the engine is only  generating around
45 to 50 HP at 62 MPH or 100 Km per hour.

Paul Lamar