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They alter the parameters in the ECU to make it seek a higher torque target which will of course lead to higher boost pressures. Nothing magic really, just altering the set points just as they alter the boost pressure set points with the T7.
The T7's use an air flow mass rate meter. The T5's don't. The C900's used the air mass flow meters (MAF). So the technology has come full circle. Note that if they wanted to, they could have built a torque target boost control from the T5 base if they wanted to. The T5 is aware of the air flows and fuel flows which are proportional to torque. From my point of view, the MAF system increases the cost of production over the T5's speed-density system. So there must have been a strong motivation to go with the MAF based design. The increased fuel efficiencies suggest to me that that was the reason to go back to the MAF based systems. That implies better control over the AF mixture and I can only assume that this produces less emissions, beyond the obvious reduction in CO2.
The ECU controls the torque by controlling the air mass flow rate, more air=more O2=more torque. The torque objective is reduced in the lower gears to prevent wheel speed or excessive grinning. The air mass flow is directly measured by the MAF sensor, so its quite simple. Nothing obscure with the DI is involved. However, if the fuel sucks, fouled injectors produce a poor spray pattern, plugs are worn or incorrect, fuel pressure is low... knocking conditions can occur and the ECU and DI will sense such conditions and produce less agressive ignition timing and will also reduce the boost pressure and air flows to avoid knocking. So the knock avoidance is quite independant of boost/torque control when the system and fuel is right.
It was reported by Dr. Boost that many of the octane booster products that you can buy can interfere with the ion behaviour in the spark gap, and the DI function can actually reduce power and boost when octane boosters are used or used excessively. So not all octane is octane as far as the T5 and T7's are concerned.
posted by 208.24.179...
, Tue, 14 Jan 2003 14:40:34
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