Backpressure — The Engine Killer No One Explains Properly

Saying back pressure is good for your engine is like saying air resistance is good for accelerating. It's just wrong. Let me tell you why. As your piston goes up in the exhaust stroke, it pushes exhaust out of the cylinder, and the less back pressure there is, the easier the piston goes up and the faster a new intake stroke can begin. That's just how it works. But people very commonly confuse back pressure with exhaust scavenging, which is when each exhaust pulse pulls a vacuum behind it to pull the next exhaust pulse out. You probably also heard the phrase, oh well, a little back pressure is good for low-end torque. This is also wrong. The only reason you'll notice a slight difference at the low end is because with more exhaust gases left in the combustion chamber due to that back pressure that you're talking about, the original charge of fuel and air burns cooler because exhaust is an inert gas. This uses the same principle as EGR, which is absolute garbage and destroys your engine. It all comes down to engine tuning. Instead of tricking your engine into making more power at the low end with back pressure, if you tune it properly to advance ignition timing at the low end and inject more fuel so it would be less prone to knock, then you would add plenty of low-end torque the proper and safe way. So why do people still believe back pressure is good? Because an old-school carbureted or poorly tuned engines opening up the exhaust sometimes produced low-end torque since the engine was tuned for a certain amount of exhaust reversion and scavenging, but that was due to incorrect tuning, not a need for back pressure itself. Most modern engines have small diameter exhausts to increase gas velocity, which can improve scavenging effect at low RPM, but this is a matter of wave tuning and cross-sectional area optimization, not static back pressure. And this benefits auto manufacturers since most people stay in the low RPMs for fuel efficiency and also lug their engine quite a bit. Good scavenging is from exhaust tuning, pulse timing, length, diameter, and absolutely not from restrictive static back pressure. So subscribe if you want the truth about engines and stay tuned for more data-driven info. Thanks for watching.