Step 1)
Make sure your vehicle is in proper working condition. Fresh spark plugs with a good gap (and proper heat range). Proper octane fuel for the power level. No boost leaks (especially on a MAS based system), proper supporting mods for the intended power levels.
Do a boost leak test BEFORE you attempt to tune on a MAS based system.
In case you didn't catch that....
CHECK YOUR CAR OVER BEFORE YOU TRY TO TUNE IT. Mechanical problems will fester and destroy your tuning budget.
Now we all know here that an engine is just a giant air pump. Three things are required to make power. Oxygen, Octane, and Ignition. Compression comes naturally due to how the engine should be working, if you don't have compression, see step #1. With more oxygen, more octane is required. When they balance out correctly you get power. Ignition is used to control the burn and make sure you have equal burn across the cylinder. This isn't rocket science guys and the factory was pretty good for optimum ignition timing for a XX amount of air and XX amount of fuel molecules (aka power level), and the factories math holds fairly true for quite some power over stock.
Step 2) What fueling system are you using? MAS or Speed Density? (These are the two options everyone here should be using).
This post I will cover MAS based systems, the next post I will get into speed density and standalones.
Step 2a)
MAS: Mass Airflow Sensor
How a MAS sensor works is purely math. On most systems there is a wire there that physically counts air molecules that hit it. The sensor is programmed with its overall flow area and knows that xx air molecules over xx sq inches= xx flow rate. Until you reach the flow maximum of a sensor, this formula will remain the same. Now it isn't exponential, it is more of a curve that gradually tapers out at a certain HZ value, for arguments sake, lets call it 3000hz.
Now at idle most cars are low on airflow, typically between 10-100hz. Because of this you only need so many fuel molecules to maintain the 14.7molecules of air to: 1 molecule of fuel ratio.
Now there are two types of MAS sensors, hot wire and hot filament. The pretty much function the same.
The sensors in our cars are called Karmen Vortex MAS sensors. They are a bit more advanced as they measure pressure waves/turbulence changes. More airflow=more turbulence. Instead of a heated element/wire catching air molecules the sensor measures waves using a LED, mirror, and photo receptor. Pretty much it uses these together to measure fluctuations in pressure. I would concern myself with how the function differently from a MAS sensor because the principal is pretty much the same and they tune fairly similar.
Important MAF system facts:
A)If you decide to mess/move your MAS sensor remember a few things.
1)It is designed in a DRAW THRU environment only. I am sure people have put them in blow-thru (in fact I've seen it like that on a supercharged 3000gt, I won't name the kit as this isn't the purpose of this thread) but Mitsubishi designed it to pull thru.
2) MAS sensors are very sensitive to turbulence. Sharp bends before or after the MAS wires/pressure chambers will cause falsified readings. MAS sensor will double/triple/quadruple count air molecules and that will play hell for your fueling maps.
B) It is a calculated fuel system. This means if you tune with boost leaks, you are shooting yourself in the foot! XXXhertz measured by the MAS sensor should mean XXXhertz in the throttle body. When you loose air, your ecu is still expecting the air to be there and will inject the appropriate amount of fuel (pending you have enough injector left), this means you will run rich. On another side note, the factory knows the compressor maps for your compressor wheels. I knows where the efficiency island is and where the engine is running from the factory. They know how efficient the intercooler are. They understand what the intake air temperatures are going to be at the inlet valve under most conditions. This is why the karmen vortex meter has a intake air temperature sensor at the MAS as it uses this information to scale the fuel/timing maps slightly. When you change turbochargers, you change efficiency and need to tune appropriately for it. Intercooler changes changes can also throw off how a vehicle runs. Now most td04 setups are fairly close at lower boost levels (and mostly the same in cruising obviously), as long as you size your injectors properly, you will be fine.
Why can't I run huge injectors on my MAS system?
1)Why bother? Again, you can use math to determine how much fuel is required for xxxawhp. Size your injectors correctly and you will save headaches. Since you are using a piggyback, all you are able to do (most of the time) is to scale your larger injectors to match your desired Air/Fuel ratio on the factory maps. If your injectors are 20% larger than stock, then odds are you will need to remove roughly 20% fuel at WOT/open loop fueling to make it roughly the same.
I guess I should get into how an injector works. Injectors are rated in flow rate and duty cycle. Most modern injectors are not recommended to run over 90% duty cycle, I shoot for 85% duty cycle to be safe. Duty cycle is defined as how many Milliseconds the injector is open for.[Duty cycle= (pulsewidth)/ (total time between ignition events)] You must remember that injectors are "charged" like a coil and there is a specific amount of dead time required for the injector to open.
Also on another side note, injectors are linear in flow until under 1ms of flow. There is a certain slope aka flow rate an injector follows. XX increase in psi = xx increase in flow increase. Now at very low duty cycles the slope is actually higher (aka your injector is larger) because the injector rams open so quickly it creates a vacuum on the other side of the pintel and fuel is forced out quicker than normal. Typically injectors are slightly larger at very low pulse widths compared to normal operations, figure a few percentage. See below. Time is MS pulse width, the breakpoint is where the injector is controlled smoothly/predictably (you can actually calculate both slopes using dead-time, injector flow rates, injector type, voltage @ the fuel injector).
Offset=dead time, aka the time it take to charge the coil inside of the injector to fire it open.
not my picture but one I found on google that is pretty good!
Why does this matter? Well remember that you need the least amount of fuel at idle. So good luck getting your 880cc injectors to idle with a MAS setup without seriously tweaking the system.
Finally the last bit on injectors. Injector drivers play a huge role on how much of that injector you are actually getting (see dead time). If the drivers aren't very good/universal/sloppy (aka AEM), you will need to compensate for this and run a slightly larger injector. We have found out that +100cc injector will usually put you roughly to what you should calculate using a factory ECU. So for all of you piggyback guys, follow the advise of the old school senior members on here, use the math. The factory ecu is VERY GOOD at controlling the stock style injectors. Also remember that there is also a small amount of close deadtime but it is nothing compared to opening deadtime. Lower battery voltage also increases injector deadtime as it takes longer to charge.
Now that we have some basics covered, lets get into it.
Step 2b) Speed Density systems
FACTS:
Speed density tuning is not as accurate as MAS based systems.
Speed density tuning supports more power capabilities than MAS based systems.
I figured we would start with that. Since we are merely calculating air density, instead of measuring, air density, we can not get it as perfect as a MAS based system. Fortunately most speed density cars are for more power than stock and most owners don't care about 100% perfect reliability in all weather conditions. Sacrifices are made for power potential.
How a speed density system calculates required fuel is different from a MAS based system. The system relies heavily on a few items.
1) an accurate MAP (Manifold Absolute Pressure) sensor
2) an accurate IAT (Intake Air Temperature) sensor
3) an accurate engine rpm pickup
4) known engine VE (Volumetric Efficiency)
The first 3 are really easy to work with. Fortunally for this community AEM (for those so inclined) as a pretty decent "base map" for number 4. I believe Grayson as posted a few great basemaps for the e-manage crowd. I know Trevor has also posted some great MAP ECU data files as well.
Now a Map sensor needs to be mounted in a location where it will get a CLEAN pressure signal and vacuum signal.
AIT sensors need to be mounted as close to valve inlet air temperatures as possible. I usually recommend the "y" pipe or upper intercooler pipe before the throttle body.
Some helpful tips:
The neat thing about speed density tuning is it is very fast to tune, much faster than MAS based systems. If you use features like "boost comp tuning" in the AEM EMS, you can get fueling maps dialed in pretty good/perfect in under 2 hours.
Your fuel demand should follow your torque curve, which should follow your engine VE. Does that make sense? As RPM goes up, fueling demands increase until peak torque is obtained (assuming airflow numbers stay the same, aka boost pressure). As you pass peak torque your engine VE will decrease and thus your demand for fuel while obtaining the same A/F ratio.
continued here:
How to tune a car, step by step.