Modern passenger car engines have been “down-sized” for improved fueludconsumption, resulting in high speeds to obtain good performance. Consumers,udhowever, are demanding improved low-end torque for improved drivability. Theudtarget engine; a 4 valve per cylinder, 1.6L engine with two intake cam profiles and 2udintake runner lengths, was modeled and correlated with measured engineudperformance characteristics (power, torque, etc.); and pressure traces fromudcombustion chamber, intake and exhaust manifolds to establish the confidence leveludin the model's prediction. The model was then optimised for low-end torque byudmanipulating exhaust manifold configuration, exhaust runner length, intake diameterudand intake runner length. It was found that the original exhaust system is too shortudand gives uneven exhaust cross-charging among the cylinders. Simulation resultudindicated that a 2.7-5.6% improvement in torque could be realised with an evenlyudcross-charged and longer exhaust runner. A 2% torque improvement was predictedudby changing the intake manifold geometry to smaller diameter. The target engineudwas subsequently modified with new set of exhaust manifold and intake runner.udResult showed a torque improvement of 2.7-4.5% at lower engine speed over theudbase design by exhaust tuning. Effect of intake tuning was not significant but itudshowed a similar trend as indicated by simulation.
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