Thinking about it from right angles.
The air pump would cool down the exhaust gases, most NOx reactions
occur at extremely high temperatures, that is not in the
cylinders, but at the top of the manifold. Having air injected in
might there for lower NOx gasses. Lower back pressure will allow
the gasses to pass through the system faster, this allows less
time for the reaction to occur before the gasses have cooled enough
to stop the reaction.
Lower back pressure may lead to high HC emissions, but at the same
time lower NO reactions. Maybe what you should do is to go with the
lower back pressure, then alter your system to lean out the mixture
in the first place. It means a hotter flame so more NO2 but the lower
back pressure takes Cairo of that???
Have a play.
What are the rules anyway, here I think it's 5% CO for older cars.
Not as strict anyway, becuse we still have leaded petrol.
Reminds me I must try and wean my car off that stuff, see what happens.
--
James Carpenter
Yellow '79 spit wired by a trained marmot
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