Ramblings of an old tuner
Preface:
ITT: I am going to talk about general tuning based on my experience of building and tuning (Some of the fastest)
boosted 3800s, a boosted version of every 4cyl ecotec, boosted LS based v8s with every possible transmission
configuration including a boat jet drive, for the last 10 years, as well as my extensive experience building and
tuning standalone/piggy back systems (AEM,Haltec,MAPecu,Megasquirt,PowerFC,Apexi Piggybacks,Greddy Emanage).
These tuning situations are all based on expereince for every different motorsport you could imagine, recreational street
racing, serious drag racing, serious roll racing, autocross, racing track days, pro/am level drifing.
I am going to seperate information in this thread between "Fact / Science" type things you will commonly find out
there on the internet in BOLD and "3800 specific / Personal Opinion" in plain text. MANY of these things
will contridict what you may find on other forums, or not be excatly what your grandpa told you when you first put
a 3.4 pulley on your GTP. I'm not saying I hate your grandpa, I'm also not saying that he is wrong.. What I am
saying is things change when you look at problems in a larger frame of reference, one your grandpa may or may not
be familiar with.
Tuning in general:
What is tuning? Well first off let me say that tuning differs completely based on your frame of reference.
"Ideal" tuning can mean many things:
- Ideal emmissions?
- Ideal MPG?
- Ideal horsepower?
- Ideal duty cycle (how long can i make the power Im making)?
- Ideal noise/vibration/harmonics characateristics?
These are common metrics of what makes a "good tune" compared to a "bad tune". If you were to judge a tune these
would be the 5 catagories you could judge them on. It gets even more complicated that some judges will COMPLETELY
IGNORE some of these catagories based on personal preference.. there are NO RULES here, they are just some
guidelines to consider for later.
So you have a stock (yes if you have a hot air intake, headers, bigger rockers, whatever you are still stock) and
you want a tune? Ill tell you right now that GM was looking at everything on that list of "good tune" items and it
cared about 3 of the 5 items more than anything else.. Emmissions, Duty cycle, and NVH. MPG and horsepower were
the last things they cared about so it will be the most commonly sacrificed items in that tune. Knowing this is
THE ABSOLUTE KEY to making changes that YOU want inorder to fufill your desires.
Now the question is what do you want... You are going to have to make some trade offs here... Want your trans to
"shift better"? Going to be some increase in NVH there. Want more MPG? Well trade out some of your emmissions
tuning. Want more power? Well trade out some of your duty cycle. IMO the GTP comes with a very aggressive
horsepower tune on it from the factory, the AFR in PE and timing tables are good enough to set all the records you want in terms of horsepower. There is very little torque management for the trans, and what little bit you have is very functional!.
PCM/ECU/TCU
Lets look at some hardware. For the most part every car in existance has 1 ecu and one tcu. In the case of a
manual trans the TCU is your right arm and left foot.
--GM/Ford/Chrysler ~1996 and newer ECU/TCU:--
OEM ECU's are farmed out to teir1 developers, so really there is nothing similar between many of these ecus. Most
of the calibration and engineering on the software developed on these are done by different teams, with different
goals and usually different development enviornments. So that being said they are all the same, but completely
different... In some cases the TCU and ECU are combined into 1 "PCM" (powertrain control module). 3800s have a
PCM
In order to read and write from these ecu's you can use some basic commands to open up the read/write channel on
the obd2 serial bus. You can then read or write the entire or partial BIN (operating system) file off the ECU.
Once you have the operating system file, you can make changes to it and load it back onto the ECU. This requires
that you know how the oprating system file is structured. This structure can be reverse engineered, or extracted
from tier1's, or stolen from calibrators, or stolen from people that obtained it.... Most people buy it (HPTuners,
DHP powrtuner (tinytuner), EFI live, JET DST).
Most all OEM systems operate on a MAF system, which i will describe below. Some OEM calibrations work on a hybrid
of MAP and MAF THE 3800 SYSTEM DOES NOT USE A MAP SENSOR
Considering for now that the hardware inside of a OEM ecu is identical to what you would find in a standalone, I
will outline a basic list of hardware found inside any ECU in the next section.
--Standalones--
Standalones such as the Megasquirt function THE SAME as OEM ECU's do, except they are all based on one generic set
of code/hardware that is lightly tweaked to work on specific platforms. The advantage to a standalone over a
OEM ecu is the fact that the software AND the calibration software were written together and designed for amatures to do the tweaking. The disadvantage is the fact that the integration to your specific car is more or less your responsiblity, even if its a "proven" setup.
What makes a ECU:
Processor/memory- This holds the software program, and processes the electicial input and output signals of the
system. These signals are always in binary format 1 or 0, up or down, high or low.
Drivers - These are the outputs of the system. These are transistors that sit on the processors low
voltage/current switches and provide outputs to things like : injectors, idle control, fan relays, etc.
Inputs - There are a few main types of inputs processors in an ECU. Because the central processor can only read a
1 or a 0 the input will clean any type of input into a digital one. MAF sensors output a frequency wave that is converted into a stream of 1s and 0s and the processor can read the speed at which the 1 and 0s switch. Voltage inputs operate with a similar filter.
Most standalones you will find will work on whats called a speed density system, which I will describe below.
--Piggybacks--
Piggybacks are any loose definition of a system that modifies what goes in or out of a OEM ecu. Common piggybacks
include: AEM FIC, MAPecu, GreddyEmanage, Apexi SAFC, DSM Maf Translator Pro, ZZP AFC 2.x / ICCU. These all differ
completely. The key to making a piggyback work is understanding and controlling all the things that the stock
ecu is doing, and understanding why it does those things
----------------Fueling---------------------
This section is on fueling....
All of the information above on ECU's is the in's and out's on what determines how often your injectors come on.
The math behind that will be completed below.
Injectors: Injectors are designed a few ways(high/low impedance, peak and hold vs constant voltage, top feed vs side feed, Big/small), but they all operate with a few key characteristics, the main one is the fact that they are pintles that are operated by electro magnets. The ECU will create a ground charge the electro magnets via a constant 12v power source. When the Injector is charged it creates a magnetic field that moves the pintle off the base and allows fuel to flow. The amount of time it takes from the injector to be charged to the first instance of fuel flowing is called the injector dead time. The injector dead time is a measurement of time, fuel pressure and system voltage have a large effect on this time. Injector closing time is usually too small and consistant to be measured.
The amount of time the injector is open will determine how much fuel will flow through it. Injectors come in different sizes but for the most part they all flow as rated when they are open. The injectors will open for as long as the ecu keeps them energized. The ECU will have a few different straigies as to how they will open injectors:
Sequential Injection/Batch injection-
Sequential injection means that each cylinder gets an injector, and each cylinder will get a spray of fuel once per intake cycle (1 of 4 cycles of a 4cycle engine).
Batch injection implies that more than one injection event happens per power cycle. The most common batch fire systems will trigger injection once every exhaust stroke, and intake stroke.
For the most part, you dont care about sequential injection. In all (the ones I know about anyway) sequential injection systems it will go to a batch system at some unknown RPM, as the injectors become too small to keep up.
HOW LONG DO I OPEN THE INJECTORS?
This is where math comes in... How long do you open the injectors and when? Well actually the hard part is not figuring out anything with fuel... You know that xxx pressure and xxx injector size will move a specific amoutn of fuel. So all thats left to do is figure out how much air is coming into the motor. I am going to outline 3 different schools on this, along with some pseudo math. The math involved below has NOTHING to do with fuel, it is simply how to determine how much air is coming into the motor.
Alpha-n:
This is a function of RPM vs TPS. This is a simple injection system that looks at how much you move the throttle compared to how quickly the RPMs increase. This system functions on 2 lambda values.. AE lambda (tps vs time) x RPM Lambda (rpm vs time). Add 2 reference tables in to whatever design you want, and you get a functional volumetric efficency calculation out of it, which equals how much air you are sucking in.
Speed Density:
This is a function of MAP and RPM. There is a table that determines your volumentric effiency based on how much engine vacuum or positive pressure you have inbside the intake manifold. This system is the most basic and common EFI stratigies out there.
Mass Flow sensor:
This is a function of a mass air sensor. Mass air sensors are built many ways (flappy door, hot wire, and Karmon Vortex are common), but they all function the same... They will output a frequency or voltage based on how much air is flowing through them... more air more voltage/frequency. The ecu holds a reference table for this sensor.
MODIFIERS
Now the ECU knows how much air is coming in (most systems use the IAT or Engine coolant temperature as a modifier to help make that calculation more accurate in various ways), it wants to make some changes to it depending on how far from stoich (the perfect air fuel ratio) for some conditions:
Acceleration enrichment - add more fuel on large throttle changes
Power Enrichment - add more fuel at wide open or in boost
Deceleration Enleanment - cut fuel during deceleration
Cold start Enrichment - add fuel for starting.
lean cruise - remove fuel for crusing.
o2 sensor/closed loop - How far off am I on my math via the o2 sensor systems feedback
--Closed loop --
GM closed loop systems are VERY accurate. They use Narrowband o2 sensors that detect 1.0 lambda with very high accuracy. Unfortunatly if you have an exhaust leak or a misfire that lets fresh air/oxygen into the system it will detect more air and the assumption that no unburned air in the system will render the system usless. The amount of air in the exhaust can be changed by cam profile as well, so all closed loop systems are designed to monitor the amount of expected air in the system. Adding a large cam to any motor will throw off this value by a constant ammount, so it will have less of an effect at higher airflow areas.
-Injector configuration-
Injector data in a PCM will typically include a "offset" table, and a "flow table".
The flow table will take a flow value in, and convert it to pulsewidth, and calculate the batch/sequential math for us. This is typically not adjustable information beyond the input value.
Offset tables come in many different appearances, most common ones are voltage and pressure... lower voltage = higher injector offsets required
--Power Enrichment
This is a section I believe alot of people will take interest to, I will try to put in some of my ramblings based on e85 and pump gas here later.
3800s/most things: For e85, your ideal AFR in power enrichment is between 10.8 and 13.0. For 93 octane ideal AFR is between 11.2 and 12.2. For leaded race gas ideal AFR is between 11.8 and 12.5.
When you are looking at air intake temps that exceed the limits of your heads/octane you can add fuel between .5-1.0 points to cool your air charge and effectively increase octane.
---Timing / ignition----
I am not going to go into ignition here. If you want to understand how spark happens google around a bit.
To make things easy, the ECM drives spark based on RPM and crank position. The spark happens BEFORE the piston is at top dead center (BTDC). All motors have an "ideal spark" called MBT Mean Best Torque spark that happens at any given time, ideal power is around this number. The timing of the spark happening is measured in degrees. As the engine spins faster or slower, and depending on how much air is being compressed in the cylinder this degree changes.
Blowing up fuel in the cylinder happens 3 ways.
Ideal: Spark ignights and it begins to burn and by the time the piston has reached the top of the cylinder it has built a flame front to the end of the fuel cloud and is ready to start expanding creating power on the piston.
Knock: Spark happens too early, and it causes alot of pressure to be put on the piston due to the fuel explosion expanding before the piston has reached the top of the cylidner.
Detonation: Spark has not happened, and the fuel has ignighted due to pressure and hot spots in the cylinder.
On most all OEM tunes spark advance is always near MBT, which gives it ideal performance in most all situations. Modifications to this spark will produce better results when running non stoich AFR. Determining how much better or worse changes to timing make is not an excat science, and can be done many ways. On 3800's I suggest that stock timing is good for both 93 octane and E85. For race gas I suggest more than stock timing and for high power pump gas I suggest a few degrees less.
Originally Posted by Sven The Sexman
