Al Gietzen wrote:

For those of us that are using TWM throttle bodies, or similar configuration
with individual throttle plates for each runner and MAP ports downstream;
MAP sensing is a different ball game.  For both the ECU and MP referenced
fuel pressure regulators, pulse filtering is required for proper operation,
especially toward the low end of rpm and power.  If you don?t have this
configuration, you can stop here.

We have already determined that some means of pulse damping was necessary
with Tracy?s ECU for smooth running below about 2000 rpm.  I had initially
just added some volume using a section of bigger hose, which helped
considerable, but wanted to do some further work to try and decide how best
to set it up.

Regarding FP regulator; this week I installed a dial type fuel pressure
gauge to use to calibrate the EM2.  With engine off, running one fuel pump
gave a nice steady reading of 42 psi, and both pumps gave 43.5; which is the
3-bar setting that TWM said to expect.  What surprised me was that with the
engine running at 2000, the pointer was swinging very rapidly over a range
of over a pretty wide range; from about 27 to 37 psi.  It is an undamped
bourdon-tube gauge, responding to a lot of pulsing.  I had no pulse
filtering between the manifold and the fuel pressure regulator.

I also was noting that at a fixed throttle setting the MAP pressure readout
on EM2 was varying over about 1? with the different samplings.  Long story
short; after some modeling, I started on the side of too much damping.  I
now have a bit over 2 cu. in. of volume in the line from the MAP ports (the
ports from each of the three runners connected together), then a 0.025?
orifice restrictor, and then a T that goes to the EC2 and back to the FP
regulator (about 1 cu. in. volume).  The fuel pressure gauge is now quite
steady at about 32 psi for those same conditions; and the MAP readout is
steady.

The volume downstream from the orifice (to the EC2 and the FP regulator) is
now a bit too large making the response too slow.  Its fine for the normal
slow power changes, but I noted that pulling the throttle rapidly back to
idle results in a dead spot while the mixture is too rich (MAP decaying too
slowly).  The response can be varied by varying the volume downstream from
the orifice, or changing the orifice diameter.  I intend to reduce the
volume I have in the line to the EC2.

If you want to think about it, consider the volume in the line as a spring
(linear with force, more volume = weaker spring), and the restrictor as a
hydraulic damper (flow varying with about the cube root of the force; I
think; smaller diameter = more damping).  Best not to think about it too
hard, cuz it?s not that critical.

Al

The Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2004 All world wide rights reserved.