Hello Paul-

Sent this to Tracy earlier today; thought I would pass it along in case
someone on the list has seen this before...

Had some peculiar behaviors in that latest tuning attempts.  Hopefully
you'll have some suggestions.

Background-

   - 13b, p-ported, with slide throttle design & "tuned" intakes
   - LS1 injectors
   - EC2 with latest p-port firmware
   - EM2
   - 6800 field altitude
   - 55F OAT
   - Known to be under propped (has a 72x72 160hp 2-bladed prop.  Needs a
   72x109 230hp 3-bladed prop)

Symptoms-

If we run the engine with the manifold pressure lines *DISCONNECTED *from
the EC2:

   - Engine starts very easily
   - The engine runs quite smoothly across a pretty wide rpm band after
   tweaking the manual mixture control.
   - Reasonably smooth running as low as 1500rpm engine (526rpm prop!)
   - Very smooth running 3000 - 4800 RPM.
   - Above 4800 rpm we seem to "run out of enrichen" on the manual mixture
   control & the engine stops.
   - MAP table view on the EM2 real-time shows the EC2 using map location 59
   or 91 (MP constant matching atmospheric pressure) depending on high/low
   throttle (as expected)


If we run the engine with the manifold pressure lines *CONNECTED *to the
EC2:

   - Engine noticeably harder to start
   - Engine will not run smoothly at any rpm
   - Significant surging pattern -- rpm increases rapidly, followed by
   engine stumble to low idle rpm, followed by next surge.
   - Engine often stops during the stumble / hard to restart
   - MP pressure varies rapidly based on engine rpm
   - Significant manual mixture changes can help ease the surges somewhat,
   but never enough to get the engine to smooth out enough to let us see if MAP
   values could be tweaked.


Looking at the MAP table with engine off, it seems like all map cells are at
0 -- as expected.  I did not check all 127 cells, only the top cells (say
100 - 127).

Mark (Rocky Mtn High)

That is good evidence the 555 system will work fine :)

We noticed this phenomena on the dyno test of your engine.

I am not privy to Tracy source code but the last time I talked to him
about it was a couple of years ago and he was taking only one sample
of the intake manifold pressure per e-shaft revolution.

Using a computer this takes only about 10 usec.
http://en.wikipedia.org/wiki/Microsecond
Light travels only one mile in FIVE microseconds.

That is 10 millionths of a second. 100 usec is one msec or one thousands
of a second. This is a very brief period of time so the manifold pressure
is jumping around a lot in a p-port tuned manifold. It could be anything
or even above atmospheric pressure at some times. That is what p-port tuned
manifolds do. See the enclosed chart. A lot depends on WHEN you sample
the pressure. It changes with RPM in unpredictable and mysterious ways.

IMHO this is confusing the heck out of Tracy's computer. IMHO you need
to feed the manifold pressure  from both intake tubes past the slide throttle
using very small hoses into a beer can and then tap out of the beer can with
one normal size hose going to the pressure sensor in the computer. Hopefully
this will damp the pulsations and average the intake manifold pressure.

Al Gietzen tried this as I recall and it did not seem
to change anything. I don't know what size hose Al used
but I think very small hose is essential. On the order of .030
inside diameter or smaller.

Paul Lamar