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.

Paul Lamar


Great info, Paul.  I wasn't surprised to see the difference between a
rotary and a piston engine.  This is just one of the reasons why the
rotaries produce so much power for their size.

I believe only the true frictional losses should be included in correcting
power numbers.

Gary Knutson


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