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Do You Want A Lean OR Rich AFR? | Fuel VS Power! - YouTube
Channel: High Performance Academy
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Air fuel ratio is undoubtedly one of the most
misunderstood topics when it comes
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to the world of EFI tuning.
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We only need to ask on any forum what
air fuel ratio should I run my car at,
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and you're likely to get as many different
answers as you have people
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contributing to this thread.
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In this free lesson, we're going to find
out how the air fuel ratio affects
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the engine's performance, specifically
with the amount of power
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the engine makes.
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While the amount of power an engine
produces is related to the chosen
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air fuel ratio, it's not as critical as many
people think.
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The amount of power the engine can produce
is actually defined by the amount of air
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that the engine can consume during the
intake stroke.
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What we need to do is supply sufficient fuel
to make sure that we properly combust
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all of the available oxygen.
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To do this under full load, we'll be running
the engine richer than stoichiometric
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and there are a couple of reasons for this.
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Firstly we want to add additional fuel
to make sure all of the oxygen is
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mixed with fuel.
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This ensures we're releasing all of the
available power from the engine.
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Secondly we're using the extra fuel to
quench or cool the combustion charge
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and hence control the combustion
temperature.
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This is critical to the safety and
reliability of any engine,
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and should always take precedence
over outright power.
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There's a widespread belief that to make
the absolute maximum power,
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any engine must be run at the absolute
lean limit which consequently can be
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a very dangerous way to tune.
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There is some truth to this belief,
but the reality is that engine power
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actually varies a very small amount over
quite a wide range of air fuel ratio.
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As an experiment we ran our Nissan
350z to show how the power was
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affected by different air fuel ratios.
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For this practical demonstration we're
going to have a look at how the lambda
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or AFR target affects torque using the
torque optimisation function on our
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Mainline chassis dyno.
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For this demonstration we're going to be
using our Nissan 350z, fitted with the
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Haltech Elitre 2500 ECU.
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Of course it's the concept that's important
here, and this is applicable to any engine
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and any engine management system.
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Let's start by having a quick look at the
Haltech laptop software so you can
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understand what I'm doing.
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So here in front of us we have our lambda
target table.
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And these are the lambda targets we
want the engine to be running.
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On the horizontal or x axis we have our
engine load measured in kPa,
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and on the vertical axis we have our engine
RPM.
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For this test we're going to be operating
at 2000 RPM and wide open throttle,
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so we're going to be operating in these
zones out here on the right hand side
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of our graph.
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Now on the right hand side of the ECU
software you can see we have our lambda
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target displayed along with the actual
measured air fuel ratio from a wideband
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sensor in the exhaust.
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You'll be able to monitor those while
we're running the engine.
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Now we'll jump across to our dyno
software and we'll have a look at what
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we've got here.
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So this is our torque optimisation screen
and on the horizontal axis we have
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our measured lambda which is coming
from the Haltech ECU.
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And on the vertical axis we've got our
engine torque which is being measured
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obviously by our dyno.
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And what's going to happen is while
we're running the engine,
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the dyno will plot the torque in real
time so we'll be able to see a curve,
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we'll be able to see that torque curve
of how it's affected by our lambda target.
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The top right hand corner of this screen
we have some live data,
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we've got our lambda value coming from
our ECU, we have our torque value,
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our engine RPM and our throttle position.
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OK so what we're going to do is start by
going to our laptop software and we're
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going to highlight the entire wide open
throttle area that the engine's going
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to be running in and I'm going to start by
targeting a very lean air fuel ratio.
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We're going to enter a target of 1.15
lambda.
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Now this is much leaner than we'd ever
expect to run a naturally aspirated engine
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at wide open throttle.
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And what I'm going to do is we'll start
at 1.15 lambda and then I'll gradually
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richen the air fuel ratio all the way
through to 0.75 lambda.
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And we'll see how those lambda values
affect our torque.
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So let's get started now, we'll go to 2000
RPM we're in fourth geat and I'll go to
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wide open throttle.
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And once the engine's stable, I'll begin
our test.
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Now the dyno's going to plot the torque,
and what I'm going to do is just drop
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our lambda target by about 0.01 lambda
every second,
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and you can see what's happening now
is that the dyno is plotting the torque
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on the screen and we're down to 0.97
lambda now.
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What you can see is as we've moved from
our very lean starting point, 1.15 lambda,
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you can see that our torque has increased,
it's hit a plateau though, now we're getting
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down to 0.88 lambda and you can see
that our torque again is starting to
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fall away.
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We're down to 0.84 now and you can
see that the torque is continuing to drop off.
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But we're going to go all the way down to
0.75 which again for a naturally aspirated
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engine running on pump fuel like this
is much richer than we'd likely run.
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Alright out test's finished now so I'll
just back off the throttle and we can
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talk about those results.
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So on our dyno screen you can see our
red line which is our torque plot.
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And you can see that there is a cross
hairs showing the point where we made
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peak torque.
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It's also being shown up here so what it's
saying is that at an air fuel ratio of 0.92
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we made our peak torque which was
342 newton metres.
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So for this particular operating point,
the peak power or peak torque was
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being produced at 0.92 lambda.
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The important point though to take
away from this is that over what is
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a relatively wide range of lambda
values, probably everything from around
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about 0.86, 0.87, through to about lambda
1.0, you can see that we've seen
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almost no change in torque across those
lambda targets.
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We've reached a plateau.
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However if we look at the very rich side
and also conversely at the very lean side
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of our graph, we can see that at both sides
of that spectrum the torque drops off
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quite sharply.
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And if we continue to go richer or
continue to go leaner,
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our torque would have dropped off
further.
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The point of the demonstration though
is that over a relatively wide range of
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lambda values, in this case around about
0.87 through to about lambda 1.00
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or 0.98, we've seen almost no change in
our engine power.
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So we can actually choose a safely rich
air fuel ratio in this case without
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sacrificing torque or power.
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For the second part of our demonstration
we're going to look at the effect of
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air fuel ratio on power during a ramp
run.
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Now we shouldn't really be expecting
anything different than what we saw
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during the torque optimisation test but
this is just another way of visualising
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exactly what's going on.
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So we're using the same car, this time
we've swapped to a Link G4 Plus ECU.
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But again the actual ECU and the engine
don't really matter.
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It's the concept that I want you to
understand.
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Let's have a look at the laptop software
and we'll see exactly what we've got in here.
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So the table that we're going to be
interested in here is our AFR lambda
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target table, this is really the only
place I'm going to be making changes.
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Now for our first run, we're going to be
targeting lambda 0.90 and you can
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see that I've filled out the entire wide
open throttle running area of that
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table with this target.
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So in this case we've got our load
manifold gauge pressure, or manifold
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pressure on the vertical axis and again
we've got RPM on the horizontal axis.
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And this lower area of the table is where
we're going to be running at
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wide open throttle.
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So let's do our first ramp run now
on the dyno and we'll see what
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result we get.
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OK so there's our first ramp run
complete there and the engine's made
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149.7 kilowatts or 200.7 horsepower
at the rear wheels.
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Now you can see that at the bottom of
the screen we have our power graph
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in kilowatts and the red line above is
our lambda target.
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And you can see our red line is running
pretty close to our target of 0.90.
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There's always going to be a little bit
of a discrepancy as we go through that run.
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So when I talk about a target of
0.90, I'm generally meaning 0.90
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plus or minus around about 0.01
lambda, that's what I would consider
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to be on target.
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OK so we've got our first run done
there.
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What I'm going to do is save that and
we will call that lambda 0.90.
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It's just so we can reference that a little
bit later on when we want to overlay
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it with our other runs.
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And for the sake of simplicity we'll show
that live on the dyno while we're doing
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our next run.
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OK let's jump back into our laptop
software and what I'm going to do now
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is highlight again that entire wide
open throttle running area.
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And this time we're going to target
0.86.
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Now remember from our torque
optimisation test we saw that our
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power was reasonably, or our torque was
reasonably consistent down to about 0.86
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lambda, so obviously I'm not expecting a
huge difference in the power during
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a ramp run.
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So let's do our second run now and we'll
see what result we get.
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So that's our second run complete there
and we've got almost exactly the same
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result, we're down around about a
kilowatt there.
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But you can see because we overlaid
those runs during that test,
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the green run which is our current
run overlays almost exactly
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with the previous run we did.
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If we look at our lambda at the top
here you can see referenced against
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our previous run, you can see that our
red line is a little bit richer as we'd
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expect and you can see that for the most
part of that run we're sitting at
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our target or very close to 0.86 lambda.
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So what we'll do is save that one now,
we'll call that 0.86 so we can
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reference it again.
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And this time we'll drop back into
our laptop software and this time I'm
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going to target 0.95 lambda.
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Again from our torque optimisation
test we saw up to at least 0.95,
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perhaps even 0.97 lambda that our
power wasn't massively influenced,
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or our torque wasn't massively
influenced.
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So again I'm not expecting a huge
difference from our ramp run power test.
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Let's do that ramp run now and we'll
see how that works out.
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So there's our third ramp run done and
you can see that our results are almost
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identical to our first run, less than half
a percent difference between those runs.
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So we've got 149.9 kilowatts or 201
horsepower at the rear wheels.
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Again because we've overlaid that with
our last graph, you can see the green run,
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our power is almost identical throughout
that entire run compared to our last
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run at 0.86 lambda.
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And again our air fuel ratio, our lambda
numbers at the top of the graph there,
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you can see that we were sitting on
our target at 0.95 plus or minus
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about 0.01 lambda.
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So the purpose of this test is simply
to show you that the power is not actually
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influenced that dramatically by our air
fuel ratio target.
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We don't need to be tuning for the
leanest possible air fuel ratio in order
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to make good power and tuning with
a richer air fuel ratio also means we've
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got extra fuel there to help control and
cool that combustion chamber temperature.
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To highlight these differences we can also
analyse the three runs overlaid with
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each other which we can see now on our
dyno screen.
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And again throughout those runs you
can see that the variation in power
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that we've got is negligible.
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We've got almost no difference.
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At the bottom of the screen here you can
see our three lambda plots,
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our purple run which was our first run
with our target of 0.90,
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the red run which was our second run
with a 0.86 lambda target,
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and then finally our light blue run which
was targeting 0.95.
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So hopefully this demonstration has gone
further to help cement and reinforce
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the concept of how our power and torque
is influenced by air fuel ratio.
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That was just one module that's been taken
out of our EFI Tuning Fundamentals Course.
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This is a complete theory based course
that will teach you the core tuning
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principles and techniques that you need
to understand in order to be able to
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correctly tune any engine, ensuring you
achieve maximum power and torque
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while most importantly ensuring engine
reliability.
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Within this course, you're going to find out
how the engine operates, how the ECU
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works, you'll learn about fuel and
ignition tables and find out what we're
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trying to achieve when we're optimising
these.
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If you want to learn more about this
course, click the link in the description.
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