EFI info for turbo use

[captain chaos]

From Arttu:

All right, here we go. Feel free to add information or correct me. But please try to keep pointless debate at minimum to keep this thread clean and readable

Typical EFI system components for bike installation

Engine management unit / Engine Control Unit (ECU)
An ECU that provides all the required features for particular application. Preferably something that can be configured and tuned as widely as possible.

Fuel injectors
Typically one injector per cylinder. In some cases (high power) it could be beneficial to use two injectors per cylinder in staged mode. Meaning that the first set of the injectors works all the time and the second set comes up at higher rpm or power level. It's also possible to use only one injector for the whole engine (Throttle Body Injection, TBI) but this gives worse fuel distribution so it's seldom used when performance is significant factor.

Fuel pump
Typically electric pump, in-tank or external. Using a suitable mechanical pump is also possible. The pump must be capable to supply enough flow for maximum power of the engine and enough pressure for proper injection. Typical fuel pressure is 2.5-3.5 bars (38-53 PSI).

Fuel pressure regulator
The regulator keeps fuel pressure constant. The regulator is often referenced to the manifold air pressure. Purpose of this is to keep pressure over the injector constant at different load conditions (=different manifold pressure). However, this isn't absolutely necessary with normally aspirated engines since the manifold pressure variation is relatively small. Many OEM bike systems with in-tank pumps have also the pressure regulator integrated with the pump and therefore they don't use manifold pressure reference.

Throttle body/bodies
Regulates air flow to the engine. Individual throttles for each cylinder (ITB) or one common throttle plate with intake plenum.

Sensors
Required sensor setup depends on the ECU but typically the basic sensor set is very similar for most of them.

Manifold Air Pressure sensor (MAP)
Measures the air pressure in the intake port. Basically measures the engine load level. Can be replaced with throttle position sensor or air mass flow sensor.

Throttle Position Sensor
Measures the throttle position. It can be used for engine load measurement and in addition it can be used to trigger acceleration enrichment. So the TPS is often included in the setup even if some other sensor is used for engine load measurement.

Intake air flow sensor / Mass air flow sensor (MAF)
Gives engine load information by measuring intake air mass or volume flow. Quite common in car application but seldom used on bikes.

Intake Air Temp sensor (IAT)
Measures temperature of intake air. Required to compensate air density changes when air temperature changes.

Engine temperature sensor / Coolant Liquid Temperature sensor (CLT)
Measures engine temperature. Required for determining correct warm-up enrichment and startup fuel amount. In practice this should measure temperature of the cylinder head since that affects most to required warm-up enrichments.

Crank position / engine RPM
In all cases the ECU needs RPM information. If the ECU controls just fuel injection simple tacho pulse input can be enough. For ignition control crank angle information is also necessary. There are various arrangements for crank angle measurement and required setup depends on the ECU. Typically one or two sensors and toothed wheel on the crank. In addition cam sensor can be used too.

Lambda / O2 sensors
Measures remaining oxygen content from exhaust and provides mixture information. Usually not absolutely necessary but very useful for tuning.

[captain chaos]

Ok, let's take a closer look to the components. Again this all is based on my limited knowledge and some parts are just my opinions. So feel free add information, correct me or just tell your point of view.

ECU

Comparing different ECU brands and models on discussion forums is often a can of worms so I not going to mention any brands in this post. But let's take a look on general features.

Sometimes you see a manufacturers advertising their ECUs by telling that they have 8/16/32/64/whatever-bit processor running at xxxMHz. In practice this kind details have very little importance for normal user. If developers have done their work they have selected powerful enough processor for required features. And then extra processing power doesn't give any benefit for the user.

Unfortunately it seems that aftermarket ECUs aren't always very thoroughly tested. So if manufacturer claims that their ECU has some feature it doesn't necessarily mean that it works in practise on all possible engines. One quite common pitfall with bike engines is crank triggering. Bike engines rew higher and faster and in addition crank rotation is very uneven during cranking compared to typical car engine. These things may cause troubles with ECUs that are mainly developed and tested for car use. So it's always a good idea to try find out if somebody has used the same ECU in similar application before investing money.

One thing that comes up quite often when comparing different ECUs is sequential injection. This means ability to time injection events for each cylinder to some specific crank position. Alternative option is batch injection which means firing all the injectors simultaneously or in two different groups. Sequential injection may look superior since it allows to inject fuel only when intake valve is open. But in practise it usually provides quite little benefit for performance. It may give slight torque improvement at low rpm but at high rpm/load it makes very little difference since the injectors are open major part of engine cycle any ways. The main reason why sequential injection is widely used in modern cars and bikes is emission control. And fuel economy too.

But for regular gear head sequential injection typically gives one interesting side feature: usually it comes with individual cylinder fuel trims. This means that you can adjust fuelling for each cylinder. This can be used to compensate differences in injector flow rates, cylinder temps, inlet tracts and so on. But keep in mind that you need some way to monitor individual cylinders to get any benefit from this.

Then it's good to pay some attention what kind sensors the ECU can use. It's nice if it can be configured for many different temp sensors, MAP sensors, crank sensors and so on. Especially crank triggering can be important thing since there is usually limited space for trigger wheel and sensors on bike engines. Or it's otherwise difficult to adapt some specific trigger setup on the engine. So it's handy if the ECU accepts various trigger arrangements and you can select on that fits best for the engine. This can be also a cost factor, in the worst case you have to use proprietary sensors from the ECU manufacturer that cost arm an leg. Downside of flexibility is complexity. If the ECU can be configured to do anything it might be challenging for beginners to get it configured.

Some kind data logging is very useful feature. Basically this means that ECU can record sensor values and it's running parameters for later viewing. Some ECUs have internal memory to store the logged data while some others needs to be connected to the tuning PC for logging. And some, typically older ones, don't support any kind logging. Usually data logs are the most important tool for tuning, especially if tuning happens on the road. On the dyno you can tune pretty well without them. Importance of internal logging memory depends on intended use. I think it's very handy in racing you can get logs from every run without carrying any extra stuff logging. For road use it's not that important since usually you need logs only when you want to do some tuning and then you can carry a laptop. But of course it's more handy if you can do logging without extra stuff.

It's also good to check what kind tuning interface the ECU uses. Most of them use tuning software running on a PC but there are few that use their own hand-held tuning box. While a dedicated box might be handier to carry and more robust their user interface is usually more limited and cumbersome compared to a PC software. Nowadays most ECUs support tuning on-the-fly while the engine is running but some may require switching to programming mode for tuning changes.

Then a list of more basic features to check before purchase:
-How many injectors it can run? And how many individual injector channels?
-Can it drive low or high impedance injectors or both?
-How many ignition output channels?
-Does it have internal coil drivers? If yes, what kind coils it can use?
-Knock sensor input and knock control?
-Boost control?
-General purpose outputs? What they can drive and how they can be controlled?
-Additional inputs?
-Launch control?
-Alternative fuel and ignition maps?
-NOS support?
-and so on...

As bottom line: Try to figure out what features you really need and then check what ECUs suit for your requirements. It's pointless to pay for all kind fancy stuff that you won't use. And try to check if somebody has really used the ECU in similar configuration before.

More to come when I have time to write it...