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So I was wondering, when taking the car on a straight in 5th gear at 3000RPM (~108km/h) or in first gear at 3000RPM (low speed), what are the differences experienced by the engine ?

Apart from airflow being better at high speed I guess, the engine still runs at the same pace. Is the fuel/air mixture different/very different ? Is it harder for the engine or are the transmission/driveshaft getting all the real hard work ?

Thanks!

  • (My underlying question being, when I go to high speeds, am I damaging the engine more than when going to low speed, even at the same RPM) – P1kachu Jul 3 '18 at 2:49
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Car engines are definitely made better today, but transmissions aren't. Stick your arm out the window as you drive and feel the wind resistance at different speeds. That's the best clue to what your transmission endures. As for the high rev operation...your computer helps the engine, but not the transmission in most cars. If your car isn't climbing up mountains or pulling trailers, it's better to shift at lower RPMS...simple as that. Most engines have torque max at the lower RPM's and Horsepower Max at higher RPM's. Transmissions need torque, not Horsepower.

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What @Old-School Engineer says is correct. Wind resistance (aka drag) increases exponentially with speed. The (simplified) formula is drag = (constant)*(velocity^2). So for example, going from 30kmh to 100kmh, the drag is 11 TIMES HIGHER. As a result, even though the engine is spinning at the same speed, it is consuming more fuel and air to maintain that RPM speed.

It sounds like you have a manual transmission. Next time you are on the road in 1st gear at an RPM of 2000, press the clutch pedal to the floor, but do not take your foot off the gas pedal. The RPMs will increase, because there is no longer a load on the engine. Next, when you are in 3rd gear at an RPM of 2000, do the same thing. This time, the RPMs will increase much higher, possibly evening getting close to red-lining. This is because even though the engine is spinning at the same speed in both cases, it is "working harder" in 3rd gear.

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