Some data from Mistral

ACRE wrote:

Fran�ois 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?

Another piece of data I can release:

- Injecting 100% of the fuel charge in the middle runners (those going into the intermediary housing) gives best BSFC (0.46 lb/hp.hr).  Injecting 100% in the outside runners gives second best BSFC
(0.485).  Any split of the fuel charge is suboptimal (50:50 gives 0.535).  Peak power is unaffected. So we use only the inside injectors, keeping the outside ones for redundancy purposes only.

This data can be released. hope it'll be useful.

Best regards,  Francois


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


Francois, nothing we have looks like those curves.
What do the torque curves look like?

Paul Lamar
 
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