Paul,

I saw where at least one other member of our group tried using the
calculators at  www.wallaceracing.com/runnertorque.php and found that the
results didn't make sense.  Here's some formulas for our 13B engines our
group may wish to test experimentally.  These are based on the underlying
principles used for the Wallace Racing calculators but adjusted to fit the
results you obtained on the Mazdatrix dyno.

    Runner length (in inches) for peak torque = 157,000/rpm.

    Runner area (in sq. in.) for peak torque =  rpm/2281


Example - How to use:

From your testing, the peak torque occurs at about 88% of the rpm for peak
h.p.

    H.P. Peak desired at 6,000 rpm.

    Peak torque occurs at .88 x 6,000 rpm = 5,280 rpm

    Runner length = 157,000/5,280 = 29.7 inches

    Runner area = 5280/2281 = 2.315 sq. in.

    Runner diameter = 2 x sq. root of  2.315/pi = 1.72 inches

I used parametric variation (which is exactly the same thing as
cut-and-try in the lab, but it sounds more sophisticated) to deduce
their equations then calculated new constants to fit the data from your
Mazdatrix dyno runs.  To see if the values made sense I checked against
the following knowns for the rotary:

I recall that the diameters and lengths of the runners on the peripheral
port you tested at Mazdatrix were intended to duplicate the LeMans engine,
and that engine had been optimized about as far as possible for road
racing.

The formulas used in the calculators at wallaceracing appear to be based
on the following premises:

1.The optimum runner length is directly inverse to the rpm.
2.There is an intake velocity that works well for a broad range of engine
configurations and rpm.

We know that the intake event on a reciprocating 4-stroke engine is driven
by 180 degrees of crankshaft travel.  Racing literature points out that as
a result of valve overlap, the intake event is actually somewhat longer.

The rotary's intake event lasts a full 360 degrees.  There's a period of
overlap, around 45 degrees, where the intake event for one chamber is
ending and and the event for the next chamber is starting.  But to the
intake runner, the events occur at 360 degree intervals.

I examined the runner length results to see how they compared.  Lengths
resulting from the above formula were 1.87 times longer than those
recommended by the Wallace calculator for a 4 cylinder 160 cu. in. engine.
 Considering how the intake event of a rotary compares with a
reciprocating engine, the ratio seems reasonable to me.

I found the resultant formula for runner area a little surprising.  Part
of the difference is due to the improved volumetric efficiency of the
rotary.

I often make a quick-and-dirty estimate of v.e. by looking at the peak
of the torque curve.  Over the years I've observed that 1 cu. in. of
displacement results in 1 ft. lb. of torque at the peak for a lot of
engines.  Your engine produced 1.25 ft. lb. per cu. in. suggesting a v.e.
of 125% compared with typical reciprocating engines.

To sound more erudite, this could all be calculated in terms of BMEP.  The
fundamental  units (force & length) are the same - but BMEP is expressed
more elegantly (and opaquely).  Converted, 1 ft. lb. per cu. in.
corresponds to a BMEP of 151 psi.  Reciprocating engines typically run
between 120 to 150 psi.

As a check of the other equation, I visited with Steve Beckham to compare
with the  final engine he and Everett Hatch built.  The intake velocity
they arrived at by independent experiment was only about 8% higher than
that resulting from the above runner area formula.

It would be desirable to design experiments to test the rpm range where
these equations apply, and to test the premises themselves.

I look forward to your comments.

Philip Groelz

Here is the Power Sport dyno power curve with the
smaller runner compared to the larger runner Lemans engine.
I am not sure what the exact length was on the power sport engine.

Paul Lamar



Philip,

Excellent post.  I was under the impression though that intake length and
diameter can change the torque peak point radically.  With the Lemans
engine with its variable length manifold and two inch ID  tubes at
maximum extension (plus 175 mm more than the immobile section)  the
torque curve peak  occurred at 6,000.

Doug in Japan