Motorcycle speed density systems

[robert dingli]

SBrady replied in refernce to Eds CCi article(s),

> I was supprised at Eds choice of a speed denisty system for a motorcycle
> engine.  Motorcycles almost always use independent runner intake systems (one
> throttle bore and carb venturi per cylinder).  If you've ever tried to
> synchronize one of these systems, it is obvious that manifold pressure varies
> so much as a function of crank position that I would think that it would be
> useless as an indicator of engine load or cylinder filling.  I also don't see
> how the fuel pressure regulator could have the frequency response to track
> these manifold pressure variations.  This is less severe at full throttle,
> but still present.

Mazda rotaries have a similar problem, especially when ported.  One option
is to place the MAP line into one of the runners and exploit the venturi
effect to give a measure of load.

Fuel pressure regulators have a suprisingly fast response time.  Connection
to only one runner would be a problem though.

> It would seem to me that an N-alpha system would be more applicable.

This is a more common solution.  Most of our rotary or motorcycle applications
use a speed-throttle position system except when turbocharged.

> It would be possible to provide some averaging of the manifold pressurer by
> using a long tube between the sensor and the manifold or manifolding the
> sensor to all the cylinders. This discussion dosn't apply if Ed used
> independent injectors and a single throttle point.

A simple method of mechanical filtering is to either have a restriction
in the line or a relatively large chamber in series to absorb cyclic 
fluctuations as an automotive muffler does.  Electronic filtering and
smart anti aliasing digital sampling can also be used.

> Once again, I really got alot out of the articles, but I'm curious about some
> of the choices that were made on the mechanical side of things.

I haven't been able to get hold of a copy in Australia.  Has anyone locally
found a source?

Robert Dingli
-- 
----------------------------------------------------------------------
             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 9344 7966                          (+613) 9344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
----------------------------------------------------------------------