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Originally Posted by wrsbmw
Like I said, it's all the moving parts, particularly the pistons and flywheel that would be affected in the engine. More work is being done by the engine in the acceleration phases than if it was just at a constant speed. Getting the energy of the car up to the requirement for a given velocity requires work to accelerate the mass of the car. After it has gained speed, it only requires additional energy to counteract friction and air resistance. The cornering requires the car slow down and speed up, repeatedly. This stresses the moving components much more than if they were just moving at a constant fixed rate.
Of course you know that city driving you get less mileage than highway and this is the same principle. More work is done by the engine in stop start or speed up and slow down than just running at constant speed. It is this additional work that dissipates the greater power and also subjects the components to dynamic stress.
Higher RPM in the lower gears are required to accelerate the car to a given velocity. You don't run the car at the top of the power band in the stretches nor would you on the highway even at 120mph. In order to get the car to the high speed, the engine must rev higher in the powerband and it must do it repeatedly when tracking the car. This puts more stress on the engine than if you were just running it up to say 120mph and leaving it at 3500 RPM in 7th gear for 30 minutes or an hour.
So yes, the engine is subject to much greater stress due to tracking because I am sure the average RPM is much higher. That is reflected in the lower gas mileage due to the greater amount of power dissipation/consumption.
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What you are saying is of course basic knowledge for any mechanically trained/skilled/knowledgeable person. Running on the autobahn and doing repeated braking and accelerations requires more energy than running at a steady 65MPH, running on a track even more than on the Autobahn (depending on track layout). But remember that the M5 engine is designed to go at maximum speed for a long time on the Autobahn, longer than you can on a race track.
My question wasn't whether a engine is more stressed on a track than it is cruising at 65MPH. The answer to that is quite obvious
My question is still if you still believe that the ///M5 engine isn't suited for extended track driving (as that was what you implied in your first post)?
And what in the engine design makes it unsuited for tracking (taking into consideration that the engine is designed to be driven extensively at 300+km/h on the Autobahn, with heavy braking and accelerations in between)?
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Of course this is also why you will wear out your car quickly by tracking it. Same thing happens in the engine. All of the moving components are affected similarly and the energy is mostly dissipated as heat. This is also why you shouldn't really race a stock car. It's not built or designed to handle the kinds of prolonged heat that the constant changing from high to low speed on a track will produce.
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If so, someone should tell BMW to reconsider ///M Driving School, ///M Track Days and the 'Ring Taxi
