hi I'm Chris from Dynojet today we're going to talk about pressure based
tuning or manifold absolute pressure (MAP) based tuning for years at Dynojet we've
been using the power commander to make adjustments based off of two inputs rpm
and throttle position for those two inputs we would output a fuel change
with the popularity of forced induction vehicles ie turbocharged or supercharged
engines it's now more appropriate for us to tune based off of manifold absolute
pressure as throttle position and manifold pressure might not be
necessarily linear we need a way to adjust the fueling based off of the
airflow going into the engine and we do this by measuring the manifold absolute
pressure and we use that for our fuel table adjustments in this video we're
going to cover some of the various units of measure for pressure how to convert
them we're also going to discuss absolute versus relative pressure I'm
going to show you how to input and configure your pressure signal into a
Power Commander PTI or CMD marine and we're also going to show you how to
create a fuel table that is based off of your pressure signal now there are
several different units of measure used for pressure predominantly what we see
is pounds per square inch Pascal's or kilo Pascal's bars and milli bars are
inches of mercury here at Dynojet we predominantly use
kilopascal and psi pounds per square inch
we can convert any unit of measure to any other unit of measure for example
fourteen point seven pounds per square inch is equal to a hundred kilo Pascal's
which is also equal to one bar which is also equal to a thousand milliliters
Furyk air at sea level also one pound per square inch is equal to six point
nine kilo Pascal's which is equal to sixty nine millibars one PSI is also
equal to two point zero three six inches of mercury now we have two ways to look
at pressure we have relative pressure which is in relation to our atmospheric
pressure and we have absolute pressure which is the same at all altitudes all
elevations all atmospheric pressures when we're looking at a boost gauge
we're used to seeing a positive value when the intake plenum is boosted and a
negative value when the intake plenum is under vacuum if we were looking at that
same pressure as absolute it would always be positive zero absolute
pressure would be a total vacuum which is only achievable in outer space here
in this chart we can see the relationship of elevation to atmospheric
absolute pressure in psi for example at sea level our atmospheric absolute
pressure is fourteen point seven pounds per square inch if we happen to be at
the top of a mountain where the elevation was six thousand feet above
sea level our atmospheric absolute pressure would be eleven point seven
eight pounds per square inch for watercraft we offer the Dynojet cmd'
marine if the watercraft happens to be originally equipped with a turbocharger
or supercharger we actually have connections to the stock manifold
absolute pressure sensor on that watercraft for the power commander all
power commanders will have an optional analog input that can be used for boost
pressure on the wire terminal strip at the top of the module we also offer the
power commander PTI PTI stands for pressure temperature input and we make
PTI power coming for vehicles that are commonly getting
equipped with turbochargers or superchargers the PTI power commander
comes with a Bosch 3 bar map sensor that also happens to have intake air
temperature referenced in the unit's we look at pressure pre-configured in the
units as absolute psi if you want to convert that to relative psi it's quite
simple so here we are in our power commander 5 software and we're currently
connected to the power commander 5 PTI unit if we want to see our current
pressure configuration we'll go to power commander tools configure pressure input
here in the PTI unit we can see that we already have configurations present this
configuration is showing absolute PSI in other words a quarter of a volt equals
one point five nine absolute psi four point seven five volts from the map
sensor equals forty four point five two absolute psi if we wanted to convert our
pressure configuration to say relative pressure in relation to our current
atmospheric pressure we would simply subtract the atmospheric pressure
quantity from these current values so let's say for example I am at sea level
and my current absolute pressure is 14.7 PSI I would simply subtract fourteen
point seven from these values so forty four point five two minus fourteen point
seven is equal to twenty nine point eight two psi so I'll type that in one
point five nine minus fourteen point seven is equal to negative thirteen
point one one so I'll type that in
now I have my pressure input configured to show relative psi at sea level click
OK now if we want to add pressure based fuel tables or ignition tables to our
tune we can go to map tools pressure tables add fuel table that's going to
automatically bring up the pressure table set up in the pressure table setup
window we can select how many columns we want inside of our pressure based fuel
table and what we want those columns to be keep in mind I've now changed the
pressure to relative so if I want to see a table that shows negative pressure and
positive pressure in relation to my atmospheric pressure I might want to
have a we'll say and we'll say a table size of 11 I want my
rightmost column to show I will say 20 psi
our leftmost column perhaps negative 20 psi we can interpolate everything in
between and now we have a pressure table that shows negative 20 minus 16 minus 12
minus 8 minus 4 0 4 8 12 16 20 click OK and now we have a pressure based fuel
table in our map file with those specified columns I can also do the same
for ignition tables
now I have an ignition table that will advance and retard the timing at various
pressures if I were setting up auto-tune I can add auto-tune tables now it's
going to ask me if I want my auto-tune style to be based off of throttle
position or pressure I really want a different air fuel ratio at any given
pressure so I'm gonna select to tune to auto tune based off of pressure so here
I have my target AFR table and my trim table for auto tune if I have this
vehicle running under vacuum or atmospheric pressure I might want to
adjust to an air fuel ratio of say 13-point O but as I increase the boost I
actually want my air fuel ratio to be richer and richer so at 4 pounds of
boost I might target 12.7 under 8 pounds we'll
go 12 point 412 pounds 12 point O and then anything over that will shoot for
11 and a half now I have a desired or a target air fuel ratio table that is
based off of manifold pressure as my manifold pressure increases my desired
air fuel ratio gets richer now that we understand manifold absolute pressure
and how to configure and set it up in your power commander V or CMD marine you
should be able to tune your forced induction engine