Another interesting article was a dyno test comparing mechanical fuel
injection to EFI on a IO-540. Page 20.

For  the IO-540 EFI system at 24 inches of manifold pressure and 2400
RPM the BSFC  was .483 and the mechanical fuel injection was .525.
About what Continental claims for my carbureted O-470 in my C182.

A 250 HP p-port two rotor BSFC properly leaned is .47.

About the same.

Paul Lamar




A little off the subject:

It's interesting that not many people seem to include friction hp into the
equation when correcting dyno numbers so that one test may truly reference
another.  There have been graphs published that show, using a test engine,
the variation in brake hp (and torque) with the time of year with highs
showing up in January and lows in July.  If friction hp is taken into
account, the graph becomes a straight line.  The variation can be quite
large and many times explains why an engine tested in July isn't a good as
it was "supposed" to be.

Friction hp, for the specific rpm, is added to observed hp and the
correction for that speed is applied. The the friction hp is then
subtracted out to give true corrected hp.  The "trick" is that the
correction factor must be applied to both the friction and observed hp
numbers.

The problem in doing this sort of testing is that many, if not most,
people don't have the friction (motoring) hp of the engine being tested.
Friction hp numbers are obtained by running a complete engine, without
spark plugs, on an electric dyno and recording the power required at each
speed.  As this number varies widely from engine to engine, depending on a
variety of reasons, this type of testing is not regularly done. With the
advent of SpinTron test equipment, more and more shops are able to get
real friction hp numbers.  I have never seen friction numbers for a
rotary, but they would certainly be interesting, from a comparison point,
to a comparable output piston engine.

Gary Knutson


I have some numbers Gary.

Here they are.


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