Quote:
Originally Posted by nick3753
Other than stepping on the toes of another more expensive model in the lineup (the M8 in this case), why would manufacturers under report power figures? Wouldn't it help sell/market to advertise the true higher values? Is there some Euro emissions or tax laws that benefit reporting a lower value? Badass looking car OP.
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That's the thing, BMW is not "underrating" anything.
Official manufacturer power rating are highly controlled and regulated by strict standards. In the past, the testing standards required manufacturers to test in steady state (constant RPM) to obtain power ratings. The engine would be run at max load at a given RPM for a few minutes to let it stabilize, take the power reading and then set at the next RPM point. This process repeated for the entire powerband. This is the most accurate and repeatable manner to rate an engine.
An engine can make different power in transient state (while accelersting) than in steady state (at constant RPM). Turbo engines, particularly ones with modern control systems, tend to make more power in transient in the mid to high RPM while making less in the lower RPM. To allow manufacturers to take advantage of these characteristics, the testing standards have been amended to allow manufacturers to chose to test in either transient or steady state. BMW has simply chosen to keep testing using the traditional steady state method for their power ratings. Since most chassis dyno tests are done in transient state, it is normal for them to show higher values than expected from the official ratings.
Further, modern engines, particularly forced induction ones, can compensate for atmospheric conditions and dyno results should therefore not be corrected, as specified by the testing standards. Shops testing on chassis dyno often still correct the numbers for atmospheric conditions, which cam falsify the results.