François Badoux wrote:

Hi Paul,

The PSRU ratio is 2.8235:1

We also hypothesized that the original Mecanair runners were too

long

so

we checked several lengths.  We found out they were just right.  I

attach

a

graph of volumetric efficiency vs runners'

length.  It doesn't include the latest data we got yesterday but

which

didn't change the message.

- TT means the length of the tubes we have on top of the engine.

- To these lengths, you have to add the length of the runners

going

from

the plenum of what we call intake manifold 1 (on the cold side of the
engine) to the junction with the tubes, and the length

of the "elbows" of manifold 2, on the hot side, all the way to the

air

intakes on the side housings.

- PL is the total length of the Primary intakes (those going into

the

intermediary housing), SL is the total length of the Secondary intakes
(those going into the front and rear housings).

- All lengths are in mm

- The pressure is MAP at WOT

You can see that the original length proved to be the best for

power

and

happens to be also the best for BSFC (well, I think... I have to check

this

with Gordon).  Its peak is also almost ideally

placed.  We tried yesterday to shorten the runners by 40 mm to

shift

the

peak to 2200 RPM (best power). We achieved that but the peak was

sensibly

lower than both the red and light blue curves.

PLEASE, take notice that this data is correct for the Mistral

manifold

and MIGHT NOT BE APPLICABLE to another manifold design.

The absolute value of VE might be understated as we believe that

our

mass air flow meter is incorrectly calibrated (reading too low air

flow

values), but it doesn't affect the message.  Do you have

an idea for easily calibrating a mass air flow meter?

Wow that is interesting. Only one has the characteristic shape of

the

tuned runner and that

is the 30.5 inch version. I am a bit confused by your messages. Is

this

the total length from port to plenum? Perhaps you are getting

reflections

from the joints. These curves are very flat for a tuned runner.
Are all four runners the same internal diameters? Perhaps we have

some

sort of harmonics going on as well.

BTW how was the VE measured?

Perhaps your plenum is acting like a dynamic chamber. Try a really

big

one.

If yours is too small all of ours are also too small.

Paul Lamar

Paul - I realize this is an old posting, but your comment that only

the

30.5

inch
length looked like tuning. I felt that the other humps were equally

valid

so

I ploted them as a factor of engine rpm. Each turn of the E shaft has

an

inlet
pulse so the basic cycles per sec is rpm/60. The yellow line on the

plot

is

theo 1/4 wave at 1100fps sonic velo,The blue, with 8 inches added to

the

length
the 1/4 wave is close fit to the measured data (red). This could

indicate

that
some feature in the manifold was acting like an added 8 inches, or

possibly

we are seeing offset from Doppler effect of the average flow velocity.

the

peaks are not high (more like bumps) suggesting a rather low eff "Q".
In any case, it makes for interesting study, and suggests a possibly
rather simple resonance system - Vance

Interesting.

I, like Taylor, am now a bit skeptical of organ pipe theory as applied
to internal combustion engine intake systems. Taylor's old work, Heinz
Heislers
recent publications and Mazda's work on the Le Mans engine all correlate
rather well.

BTW  Piston engine tuning appears to require runner lengths several

times

as long as the rotary engine tuning.

The Mistral data suggest several different resonant systems
all tuned at different frequencies are working together. As such and as

you

say the Q looks rather low. One of the possibilities is a runner of
smaller diameter when combined with a runner of larger diameter, both
the same length, will be tuned at different frequencies. Combined
they will unnecessarily broaden the curve  and lower the peak HP.

That of course implies; if all these systems
got their act together (so to speak :)) at  the same frequency the Q and

HP

would be far higher and would be in a narrower and more useful HP band
centered around 6000 to 7000 RPM.

Francois promised me some torque curves so that should add a bit if
evidence.

Paul Lamar

Hi Vance, hi Paul,

As I said in my previous email on the subject, VE seemed to be

understated

in the data we shared.  We checked into it and indeed found out an

incorrect

constant in a spreadsheet formula.  Maximum observed VE is now 102%. I

send

in attachment the revised data.
Vance's calculation of the missing 8" is spot on.  These 8" are there:

it is

the spread between the outer runners (through which the majority of the

air

flows) as they attach to the manifold.  They were not counted in the
runners' length data.

However, I don't agree with the statement that the peaks are more like
bumps.  I believe it is an effect of the scale of the graph.  On the
attached graph, I used shaft RPM on the horitontal axis, and a scale

similar

to that of the literature chart provided by Paul.  The black curve is
transposed from Paul's chart.  Its peak is at a different RPM (normal,

it's

a curve from a different engine) but the curve looks very much like a

twin

sister from those we measured.  Don't you think?

One could argue that, as our inside runners are a bit shorter (1 3/4")

than

the outer ones, our curves are in fact a superposition of two resonance
curves (or possibly 4).    Fine!  So what?  Could we raise max power by

a

couple of hp by narrowing the curve and raising its peak a bit?  Yes,

but

that would be also narrow the range of RPM at which we get max power or

very

nearly so.  I don't think the trade-off is worth it.
Gordon built 2 new intake manifolds over the holidays and we are going

to

test them this week.  I'll come back with some new data shortly.

Oh, one more interesting thing.  Some people, me included, pretended

that

you could improve the rotary's BSFC by going to aggressively lean

mixtures

(some spoke of 21:1 air/fuel ratio...) Well, tests show clearly that

BSFC

decreases as you lean the mixture until you hit an optimum, then it
increases again as you lean further. This optimum is not too bad as we

are

down to 0.455 lb/hp.hr at 75% cruise power and believe we still have a

few

percent to gain.  Of course, fuel consumption decreases as you continue
leaning but, past this optimum, power drops faster. I want to do a few

more

tests before I release the optimum A/F ratio.  Let's say that it is
definitely on the lean side of peak, but much less lean than I

personally

anticipated.  I'll elaborate an other time on the two combustion

phenomena

(well.. at least two...) that seem to be at work.

Best regards,  Francois

Excellent!! Excellent!! EXCELLENT!! You were right I was fooled by the

plot.

Next question. What are the ID's of the runners?
We will then have the last piece of the puzzle.

First good data we have ever seen on a simple tuned side port engine.
We owe a huge debt of gratitude to you Francois for sharing this
crucial data with us.

Thank you very very much.

BTW are the ports 2nd gen turbo four port or third gen turbo four port?
If second gen 200 HP is well within your grasp by switching to third gen

porting.

I know the original Mecanair engine was 2nd gen.

It has always been known if you slow down MPG increases greatly as HP

required

also decrease much more greatly. The vaunted Thielert diesel  Diamond twin

crossed the

Atlantic at 40% power :) Diesels have much much better BSFC as percentage

of power

is reduced. Cagey of them to cross the Atlantic at 40% power. You might as
well go in a boat or a hot air balloon :)

Paul Lamar

I assumed that was a Newton Meter torque curve. If so I think there is
something wrong. 100 Newton Meters is about 73 foot pounds if my conversion
is correct. Normal torque for a side port is about double that.
In any event moving the peek torque up about 2000 RPM would put
you well over 200 HP at 7500 RPM IMHO.  150 foot pounds at 7000 RPM
is 200 HP. It does look like restricted breathing. Probably porting.

Paul Lamar

So far, we got max torque of 219 Nm (162 ft-lb) at 5650 shaft rpm (2000 prop
rpm).  Basically identical to the Renesis engine.  That is with the NORMALLY
ASPIRATED G-190 which is now on the bench. We get over 260 Nm (194 ft-lb)
with the turbo G-230TS.

The runners ID are:  42mm for the outside runners and 36mm for the inside
ones as we use a 3-port block and more air is going through the outside
runners.

We have done some porting job but, I agree with you, there is maybe a little
more to be done (not much though).  However, our objective is to come with a
common port design for both NA and turbo versions to keep our part number
and manufacturing costs down.

Gordon believes we may make it to 200hp with the new intake manifold he has
designed and built over the holidays and which we'll test later this week.
A tuned exhaust system should also contribute.  Stay tuned.

Francois

Good torque numbers.
OK so that was not the torque curve plotted on here.
42 mm is 1.65" ID a bit on the shy side IMHO for good porting.
36 mm is 1.42" ID also on the shy side for good porting.
That also explains the broad banding.

I don't understand what you mean by a "3 port block".
Blocks comes in two different kinds. Four port and six port.
Four port blocks came in 2nd gen, RX8 and third gen engines.
Second gen and RX8 four port blocks ports were/are rather small.
Third gen, Cosmo and 3 rotors blocks are all the same size ports. Big!

There are two different port sizes of six port blocks. 2nd gen and RX8.
The third gen six port never made it to the US if there was such
and animal. The RX8 six port has the largest total port area of the lot.
It is known as the high power version of the RX8 engine.

Paul Lamar
 
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