You blip the throttle and your engine revs rise. It’s a fun game that can put a smile on your face as you wait for a red light to change to green. It doesn’t matter if it’s a lumbering diesel in a pickup or a muscular V-8 in a pony car, you’re likely to crack a smile when you tap that throttle. In some cars, you might just find a maniacal Joker-esque smile though, if you have an engine at the ready and it’s packing a red line of 9,000 rpm or greater. How is that possible when the average car revs to just 6,000 or 7,000 rpm? Jason Fenske from Engineering Explained is here with some answers.
First you want to figure out why an automaker might want one of its engines to rev so high. The answer is typically for power purposes. As torque remains fairly consistent across a given powerband, horsepower will rise as the revs do. So when an engine can rev higher then it will also make more power.
Jason takes a moment in the video to delve into average piston speeds. Here you find that at a certain point, an engine speeding up doesn’t have a positive effect on the power output. That’s why an AP1 Honda S2000 revs a bit higher than the later AP2 Honda S2000. The engineers discovered that they didn’t need the engine spinning as quickly, and the older 2.0-liter engine gets a higher redline compared to the later 2.2-liter unit.
After that, the engineering discussion moves to talk of reciprocating vs rotational mass and the induction of air. For example, Mazda was able to produce a high-revving engine for its RX-8 because the rotational mass of a rotary engine could spin more effectively than the reciprocating parts of a piston engine. On the air front, Honda utilized VTEC to make sure its cars were breathing properly as the revs rose. The famed VTEC crossover highlights the point when the cam profile changes, thus allowing for a greater intake valve duration and more air flowing into the engine.
Finally, Jason also brings up lower revving engines. While we enjoy the high-revving machines, it doesn’t mean that a low-revving engine is necessarily bad. It’s a different strategy employed to provide the appropriate power, be it horsepower at the high end or loads of torque at the low end.
Click play on the video above and prepare to learn a whole lot more about how an engine revs.