Tracy Crook wrote:

Subject: Dynamic chamber.

I thought about this for a couple of years off and on and I now
think I understand it. Basically what the dynamic chamber does is
double the length of the runners at low RPM and works like
a shorter runner at high RPM when the airflow is much higher.

Note the hump in the HP curve at 3000 RPM. Also Mazda does not say what
this is compared to but I suspect it is the old short four barrel carb
four port and six port manifold set up as on my 74 RX4 and my 76 Cosmo.

This is not really needed in an aircraft as we don't need more
torque at 3000 RPM. Now if you wanted to make it half the length
Mazda made it to enhance the power at 6000 RPM that might be
something to try on the dyno.

The sketch (Fig 4) is not really a simple dynamic chamber.
It is best described as a compound dynamic chamber. Or a two
speed dynamic chamber. It is something Mazda implemented on the
93 and later turbo engines. Second gen engines had a one stage
simple dynamic chamber I think. I don't have a HP curve for this
engine scanned in and the effect would be masked by the turbo anyway.
This is all discussed in Mazda SAE paper 900036.

Note also the low speed and high speed labels
are reversed in error on the sketch (Fig.4).

It is downright amazing that Mazda has continually increased the
power of the NA 13B rotary since 1974 without increasing the displacement.

Paul Lamar

My take on the data is a bit different.  When I look at the charts you sent,
I see a significant HP gain all across the rpm range, ESPECIALLY at 6000
RPM.  Also, the two stage dynamic chamber setup was used on the 89 - 91 2nd.
gen 13B, not the 93 and up 3rd Gen.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

But a gain at 6000 RPM compared to what Tracy?. An untuned six port 
four barrel manifold? Any tuned manifold would show a gain over that.
Mazda did not specifically say. They merely labeled the old curve
"Standard". They did have a diagram  of that 
manifold and carb on the same page the HP curve came from. 
Mazda SAE paper 841017.  I suspect it is not a gain at 6000 RPM 
over a simple tuned manifold tuned for 6000 RPM.

Paul Lamar
 
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