| With the engine dynamometer we will be able to construct a system analogous to what will be found in the final platform that the engine will be installed into. The engines themselves will be complete with what the customer will be installing into their vehicle so that part is identically covered. What I dont think a lot of people are aware of is the difference between mass-airflow based EFI systems and MAP (speed-density) EFI systems. The beauty of the Z32's EFI system, being mass-airflow based, is that any changes to the volumetric efficiency of the system are always accounted for by the control system. Example:
Lets take a stock TTZ and produce a tune for it. Based on the parts within the system it is going to yield a specific quantity of air mass passed through the engine over its range of operating RPM. The spoolup of the turbos is dependent on the breathe-ability of the system as a whole, which affects the quantity of air mass put through the engine at any given RPM. Lets say at 4000RPM this stock TTZ is producing 10psi of boost (0.69bar) which equates to 632CFM of air passing through the engine. That quantity of air at that RPM equates to a load value, calculated by the engine computer, which is then used by the computer to reference the fuel delivery map at load value "x" and 4000RPM. The cell within the fuel map at this position specifies an additional percentage of injector pulse time to the base calculated injection pulse required to produce a 14.7:1 fuel mixture. Now lets take that same vehicle and add a dual pop, upgraded exhaust manifolds, 2.5" inlet and charge piping, massive intercoolers, portwork, 500 series camshafts, and a full 3" exhaust. These changes to the setup are going to vastly improve the quantity of air the engine can consume at any RPM you wish to compare. So lets go back to the 4000RPM interval. At this point the setup is capable of producing 1.5bar by 4000RPM. At this boost pressure the engine is consuming 935CFM of air (vs the 632 @ 10psi). Because the engine is moving considerably more air, this will also affect the load value the ECU calculates and therefore will also cause the ECU to reference a different point in the fuel delivery map. As a tuner, because the combustion temperature at 21.75psi is considerably hotter than at 10psi of boost, you know that the fuel enrichment value in the fuel map must also be correspondingly greater to quench the combustion temperature so that you do not exceed the thermal limits of the hardparts in the engine. The difference between these two configurations have led to the engine's ability to move differing quantities of air at any given RPM interval. So, when tuning any mass-airflow based setup on an engine dynamometer it only makes sense to equip the engine with ancillary parts that will at least match the flow performance of what will actually be used in the car itself. This will allow you to configure areas of the fueling and timing maps that will cover all possible engine load conditions the engine will experience in its final configuration. The beauty of engine dynamometers is that you can produce a load that equals the engine output and hold the engine RPM static. This is a huge benefit from the tuning position as you can hold the engine's RPM, say, at 3800RPM and allow the turbos to reach full spool. This will cause the ECU to reference points in the maps that go beyond the scope of what it will actually experience in the final application. Being able to put the engine into a condition that exceeds the normal operating range it will experience when pushing the car is a huge benefit because tuning is more an art than science... the values in the maps that optimize safe performance have trends to them. Tuning right to the edge of the operating envelope, as what is done on inertial dynamometer tuning, will get the job done, if you will... But even then, inertial dynamometers dont actually load the powerplant the same as when the engine is pushing the full brunt of 3600# down the road... With an engine dynamometer we will be able to exceed the range of the real-world operating envelope within the maps to further ensure that the engine will not experience any mishaps. In essence, a brake-load engine dynamometer will allow us to even further refine the tunes for these engines as we will have full authority over RPM and load so as to accurately configure every single point in said maps..... MAP systems are entirely different.... You would have to 100% mimic the setup that the engine is going into in order to produce an accurate tune.... fortunately for us we have mass-airflow based EFI systems. =)
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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