2013 Ford Focus ST Long-Term Road Test
Edmunds.com
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2013 Ford Focus ST Long-Term Road Test
Edmunds conducts a Long-Term Test of the 2013 Ford Focus ST and dyno-tests it.
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As commented in another thread, the variations are likely due to cooling and airflow across the intercooler and a small stock turbo that is being pushed up against its normal operating range efficiency limits. The larger for the family but still small BorgWarner K03 turbo produces pretty high discharge temps coming off the compressor.--------------
When the car is on a dyno, even the biggest shop fans can't replicate the real-world air flow the frontal area of the car will see at speed out on the street. So the intercooler heat soaks, the various T-MAP (temperature and manifold absolute pressure sensors, three of which used on the 2.0L EcoBoost at various points in the intake tract) show hotter, less dense air and pressure and the Bosch torque-based engine controller tries to keep engine output power the same by increasing boost further. Charge temps climb too high for the fuel octane and ignition timing, even with direct injection allow for cooler combustion temps and you still get knock/detonation and the controller pulling back on timing and altering boost downwards. .--------------
Other owners have seen similar things on the dyno although this particular dynamometer used by Edmunds does show a little more variation between pulls. Running some higher octane fuel and longer cool down periods between pulls might verify that it is a charge temp issue although data logging would tell for sure. Also since it wasn't mentioned, the dyno operator could have did the pull in fourth gear because they think it will give better torque readings from how it loads the engine, but the longer time to accelerate in the gear creates too much combustion heat. With a good dyno able to correct and measure correctly in a lower gear anyways, I would have tested the car in third gear to see if it was more consistent if they did do all the pulls in fourth.