**Engine tuning**
To put things in perspective:

If one had an ideal engiene the amount of air it would injest, normalized to 80F at 14.5psi is:

RPM/2 for 4-stroke * Displacement * Manifold prssure/14.5 * 80F/Manifold temperature * (normalized air density at 80F and 14.5psi)

Note: we need to change F to absolute scale i.e. Rankine

This is true if the engien was ideal, but most are not, we have poor breathing due to cam timing, intake manifold design, turbo blow-thorough, etc, etc. This is all hard to calculate compared to above, hence we throw in a fudge factor called Volumetric Efficeincy (VE) which is how well we are doing versus ideal. The final air formula becomes:

Real Air Flow (at RPM and MAP and IAT) = Ideal Flow (at RPM and MAP and IAT) * VE (At RPM and MAP and IAT)

Then we need to determine the fuel requirement. This is alos not constant as load confitions change, then we have the AFR fudge factor:

Ideal Fuel Flow = Ideal Air Flow /14.7, where 14.7 is ideal AFR for gasoline

Real Fuel Flow = Real Air Flow / Real AFR

We can now understand the tuning algorithms better:

1. One can input observed VE and desired AFR into an RPMxMAP table and have the ECU run all the calc for injector timing. This will require knowledge of the injector type, its flow characteristics and Fuel Pressure. However, all of that can be dupmed into VE or AFR fudge factors,m anyway...

2. One can input some injector pulse width directly into RPMxMAP table. This is what most ECU's do. This has the effect of applying Real Flow and AFR factors together all at once. The ECU needs to extrapolate between data points to calculate for actual conditions. Since, only one fudge factor is used some precision is lost....

3. One can observe that a MAF will give the Real Flow Measurement. Then ECU needs to adjust for Real AFR and some other things (blow-by, etc) that may happen that MAF cannot measure. Hence, Phil refers to a RPMxMAP mapping of AFR'ish fudge factors for MAF that is present in this type of system. MAF systems are simple to construct in this sense. Especially if O2 sensor is used for most cruising and idling to fine-tune the fuel delivery even more.

4. For natuarally aspirated motor, MAP and IAT will depend on the RPM and throttle opening (TPS) for a given ambient temperature. This makes for a very simple system that relies on TPS and RPM, only. It is called Alpha-N. It requires ambient and water temperature adjustment. Both of these change very slowly. TPS and RPM are very easy to measure very quickly. Hence, it makes for a very quick and precise system. It is ideal for drag racing.

1 and 2 are called speed-density, since the calculation is based on engine speed and air density (= MAP adjustment * IAT adjustment).

3 is MAF.

4 is Alpha-N. N stands for RPM or engine speed and Alpha is the TPS-based factor.

All of the above, have an electronic accelerator pump i.e. fuel enrichment when the throttle is opened quickly.

A carburator is an 'analog' version of MAF. It measures air-flow by measuring pressure drop across a venturi. The more air is flowing, the greater the pressure drop i.e. Bernoulli law.

None of this is very hard. What is difficult is the careful mapping of the engine to discover optimum 'fudge factors' (VE and AFR) without blowing it up.

The aim is to have a system that can react quickly and precisely to changing engine parameters i.e. RPM, pressure and load. Hence, it depends on how fast the sensors can measure those changes. MAP and RPM measure ment is pretty fast. MAF and IAT is not so fast. TPS is just a pot, so it is instantaneous.

Anton