While the principles of tuning a turbocharged engine are no different to a naturally
aspirated one, particularly for a novice tuner faced with tuning a high boost
turbo engine, this can be daunting.
In this free lesson, we're going to see some tricks and tips to let you dial
in your tune on a turbocharged engine quickly and easily while
most importantly, ensuring engine safety and reliability.
Now we've looked at the steady state tuning process and how we can apply
that on a turbocharged engine.
However we do need to be a little bit sensible about how we apply steady
state tuning and what we're hoping to achieve.
If we've got an engine that runs a relatively low boost pressure on the
wastegate spring setting, like our Toyota, turbocharged Toyota 86
that we're using for these examples, in that case there's no reason not to
tune all the way through to wide open throttle to our minimum wastegate
spring pressure level in steady state.
And there's a very good chance that we're going to use all of that range
of the engine's operation quite regularly when we're actually driving it.
This is going to give us the most accurate results in terms of air fuel ratio and
ignition timing when we're off the dyno and we're actually driving the car.
If on the other hand though we've got an engine that is equipped with a very
high boost pressure for its wastegate spring pressure, let's say for example that the
minimum boost pressure that we can achieve is somewhere in the region of
perhaps 20 or 22 psi, somewhere around about 240 to 250 kPa, then we may want
to adapt our tuning procedure in steady state slightly.
The reason for this is it's unlikely, first of all, that we're going to use all of
that range of operation in normal driving situations.
Let's have a look at our AFR target map and I've drawn in here, a red line
representing the likely sort of boost curve we'd expect to see relative to engine RPM.
Now in this sort of engine we're likely to still be using the vacuum area for our
cruise operation and we're also going to move up into positive boost pressure
as we've already seen during normal cruise operation.
However we're going to find that particularly at higher RPM, in this case let's look at
4000 RPM where the engine is capable of making almost its full 22 psi of boost
pressure, we're going to find that there's this area here at the higher range of
the boost pressure the engine can achieve which we're very unlikely to
be able to operate in under steady state operation.
And the reason for this is that as we open the throttle further, and the engine makes
more power and torque, what happens is the engine also produces more exhaust gas
energy which helps spool and drive the turbo faster.
So what we find is that there is a certain point whereby when we're actually driving
the car, we'll find that the engine will tend to transition very quickly through
this particular area here at higher RPM and higher boost pressure.
We're not going to be able to sit steady state in this sort of operating area.
In this instance I would normally concentrate on my steady state tuning up to around
about 200 kPa or one bar of positive boost pressure.
So I would be focusing my energy in this region that I'm just drawing here.
So again we're moving up to around about 4500 RPM or 2/3 of our engine rev limiter
but we're not going to be worrying about the very high boost areas down at these RPMs,
sort of 3000, 4000, 4500 RPM.
So we're going to be focusing our steady state tuning process up to around about
200 kPa.
Now that leaves us with an untuned area and how do we approach that?
Well the next step with these sorts of engines is to transition straight into
doing wide open throttle ramp runs.
Now that sounds on the face of it a little bit scary because obviously we don't have
an idea or a shape to our fuel and ignition tables at wide open throttle
at these higher RPM areas.
In this case from what I've drawn from probably about 3500 RPM and above.
So the process is to build up very slowly with our ramp runs.
So we would start by moving through the areas we have tuned in steady state,
up to around about 3000 RPM and we can see that we've tuned in steady state there
so we know just like our normal procedure that our fuel and ignition timing
will be correct.
Then we can start moving through into the untuned areas very slowly and building
up a picture of our fuel and ignition timing as we go.
Now once we've got the engine running all the way through under wide open
throttle conditions, we can start to look at this area that we've missed here,
so we can look at our sort of higher boost area between 3000, and 4500 RPM
and we can address these areas.
Now while the engine's only going to transition through these areas very
briefly, very quickly, we don't need to be quite as precise with the fuel and ignition
timing in these areas, we still can't obviously ignore them.
So the procedure for tuning these areas is to simply interpolate the values that
we've found under wide open throttle, down to the area that we've tuned in
steady state, so in this case, I've suggested around about 200 kPa.
We can also use the interpolation function to help us fill out the volumetric efficiency
or ignition table values in areas that we haven't tuned.
Now while I recommended that when we start increasing our boost pressure,
we do so in 20 kPa increments and this would allow us to completely fill
and accurately tune both our fuel and ignition tables, there's no strict
requirement that you must do this.
And particularly when you are a little bit more confident with your tuning,
we may choose to jump ahead slightly and perhaps jump in 45 kPa increments
of boost.
So in this case, let's have a look at our volumetric efficiency table and let's say
that we had accurately tuned our fuel at 140 kPa and our next increment
was 180 kPa.
Now this leaves us with a zone at 160 kPa that we haven't accessed and we haven't
tuned so in this case what we can do is highlight between those cells,
between the cells we have tuned, and using the interpolate function,
which is the i key here, what will happen is we just simply
fill the 160 kPa zone with the value halfway between the two sites we have tuned.
Now this might not be absolutely perfect, but it's going to be very very close,
and it's a quick way of helping fill in our fuel and ignition tables in areas
that we haven't tuned.
So by this point, hopefully you've got a better idea of the way we can approach
our tuning with a turbocharged engine.
Again I want to reiterate that really the way the engine responds to both fuel
and ignition timing is no different to a naturally aspirated engine.
The only real considerations we need to make are for controlling the heat that
the engine is producing and obviously we want to limit the amount of stress that
we are placing on the engine where possible.
If you do have any further questions, please ask them in the form below,
and I'll be happy to answer them in the forum.
That was just one module taken from our complete Practical Standalone ECU Tuning course
This course is designed to teach you how to tune any aftermarket standalone engine
management system from start to finish.
We know that particularly for novice tuners it can be daunting when faced with the
task of tuning a freshly installed ECU with absolutely no base map or start file.
In this course, we present you the HPA 10 step process and by breaking the entire
tuning process down into 10 bite sized steps, each of those individual steps
is relatively quick and easy to complete.
By following that process from start to finish, in no time you've got a completely
tuned engine that's offering optimal power, optimal torque and most importantly
ensuring great engine reliability.
By following this 10 step process through, you're also going to ensure that you
don't overlook any critical steps that could waste time and money or even result
in damage to your engine.
This course is applicable to any aftermarket standalone engine management system
and any combination of engine.
To find out more about this course, click the link in the description.