Originally posted by Cate&Rob
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As a powertrain engineer I can concur with these statements. We must calibrate to meet emissions but also to allow for peak performance while being able to allow the powertrain to live well beyond the warranty period. Engines by all makers are calibrated to the same limits which are.
1) Fuel to stoichiometric fueling. This is the perfect air/fuel ratio to allow for complete and clean combustion.
2) Spark to MBT (minimum spark for best torque) spark or knock limited spark at high loads. Adding spark in the MBT region of the table adds no torque and if in excess can reduce torque. Adding spark in the knock limited region will result in spark advance being pulled back by the knock system.
3) Increase fueling at WOT or heavy loads to increase torque and power but to also cool engine components as well as the catalyst system. The higher the airflow, the higher the cylinder pressure and at some point, more fuel is needed to keep components cool and within their design parameters. Yes everyone will cool components at some point with enrichment.
4) On boosted applications, optimum boost is delivered to allow for maximum longevity of the powertrain. Believe it or not, analysis is done where the life of an engine can be determined by how many WOT events take place at each firing event and what cyclic stresses are placed on components such as pistons, rods, bearings and so on. The calibration engineer will use combustion analysis tools to ensure these peak limits are not reached. So add that tuner, to increase boost on gas or diesel? Better sell it before the warranty is up and a smart buyer should have the vehicle inspected to see if an aftermarket calibration was ever used.
I should also add...this is a gas engine topic. Diesels require a different approach but also should not be tampered with by using power adders as listed in 4).
Jim
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