ECU/spark advance/MEP

[Mike Rolica]

Mike Rolica
Meridian Magnesium Products
Strathroy, Ont 
Ext. 260


	-----Original Message-----
	From:	digi [SMTP:digi at saturn.terahertz.net]
	Sent:	Tuesday, November 30, 1999 11:48 PM
	To:	gmecm at efi332.eng.ohio-state.edu
	Subject:	ECU/spark advance/MEP

	Hello,

	As everyone knows, I'm a newbie, and I'm trying to decipher how the
ECU operates exactly, perhaps not in a electrical sense but in a fundamental
sense.
	I hear talk about a spark table, I'm assuming this is a refrence
table for
	ignition timing. Is it a multidimensional table? What factors does
the
	ignition timing depend on? eg; rpm/maf/temp/map


	yep  although map/maf is calc value from ve or lv8 respetively, temp
is just usually a bias that influences the main spark table which is usualy
map (kpa) at rpm for deg adv  ie rpm on y map on x and adv is at specific
point of xy. Maf , map is replaced with lv a load value calculated from lv8


	What about injectors? Do they operate on a static crank event or do
they have variable timing as well? eg; give them a slight headstart at
higher rpms.

	Most p4's (730, 165's ect) use batch fire. Fire 2 per rev , not
realy timed when they fire

	This is not really ECU related - but, is there a way to measure the
MEP in a cylinder on the street? MEP being maximum effective pressure, the
peak pressure in the cylinder after ignition.

	Yep  I got a little gizmo that is basically a pressure sensitive
spark plug screw it in, put plug wire on end.  Has a gauge  with 2 needles 1
reads highest reached, other is actual.. is about 20 years old, works  but
not the safest thing in the world. Tried to reset the needle once or twice
with engine running..... ouch.  Good for getting a bang on adv curve if you
know how to work cyl presure vs timing of ignition.

	Also, what about coolant/oil/exhaust temp? This subject has been
beat to death before, I have refrenced the archives, but, have failed to
understand what each fluid and its temperature affects. I have refrenced the
archives already.
	Before I get beaten! " Law of conservation of energy.... Energy
cannot be created nor destroyed.. only altered"
	Heads, cyl hot as possible without damage so A/F mix does not use
all potential energy creating heat, but mech energy.
	Oil hot so that it is at it's slipperyest point (to reduce friction
which is parasite to mech energy)
	Exaust  below 1400 f at idle! But above 900f
	I realize that specifics are unique to each type of engine(eg;
cylinder temp affected more by oil or coolant), however, I am just looking
for a general/typical answer.
	What about EGT? I have heard that retaining heat in the
manifold/headers close to the exhaust port increases velocity requiring less
work by the engine.

	Myth...Cooler air takes up less space methinks then less temp= less
volume to push through port. Done no testing though... heads with better ex
ports is easier :-)  GM's ford's exaust ports all suck!  That is why you see
dual pattern cams, longer duration on exaust to make up for the crappy flow.
I can always tell when heads are crappy by which cam they are running to
make the most power



	Would a thermocouple close to the exhaust outlet on the
manifold/headers suffice for a quick-acting EGT sensor? Or must the
thermocouple be in the airflow for adaquate effectiveness?

	The latter is correct.


	What about nitrous on EFI applications? Can you just burn a new
prom? Do you measure the nitrous flow? Whats the ideal mixture of
nitrous/air/fuel? I have seen advertisements for nitrous on EFI applications
but have not seen any information on what changes the ECU takes.


	Burning is the easy part.  Getting it right is the hard part.  When
converted to 730.. burned about 100 proms..... still no wherz near perfect
yet.  Spent all day sat and Sunday.. bout 28 hours at it


	Last thing, I saw some mention of a cone-shaped heater that
converted the gasoline to a gas state prior to entering the engine, and was
patented but dramatically increased milage. It said there was a mention of
it in the archives but I've failed to find any information on it.

	Ummmm Talk to bruce Plecan, He has A closet full of these CSH
devices, Picked one up when I went down there to visit him, Went from 32mpg
to 65mpg!  Kinda expensive though.

				Thanks all,

				- Brian