An engine makes power by filling the cylinder with fresh air and clearing out spent exhaust with as little resistance as possible. Backpressure does the opposite. It forces the piston to waste crankshaft power on the exhaust stroke, leaves more hot inert gas in the cylinder, cuts room for oxygen-rich air, and drives up combustion temperature. On a turbo engine, that problem gets bigger because turbine drive pressure is already high. Lowering pressure after the turbine improves the pressure differential across it, which can also reduce drive pressure at the inlet and take load off the piston. That is exactly why we build the Banks Monster Exhaust System as a DPF-back exhaust system focused on reducing restriction after the emissions equipment. In the Ram test shown here, lowering turbine outlet pressure with our 5-inch system also reduced pressure upstream at the turbine inlet. Less wasted work, better engine breathing, and less heat load is the whole point. The old claim that engines need a little backpressure comes from people confusing restriction with exhaust scavenging. Scavenging is a pulse effect created by properly designed runners and collectors. It is not the same thing as making the exhaust harder to push through. Restriction never helps. Good exhaust design helps the engine exhale without paying for it in parasitic loss.
The video challenges the common claim that engines need some exhaust back pressure to make power.
Exhaust back pressure is the resistance the engine must overcome to push exhaust gases through the system. That resistance can come from mufflers, emissions equipment, tubing diameter, bends, transitions, and even the air surrounding the tailpipe.
Because the engine must spend crankshaft power pushing exhaust out, back pressure represents a parasitic loss. The greater the resistance, the more power is consumed during the exhaust stroke instead of reaching the wheels.
Higher exhaust pressure forces the piston to work harder during the exhaust stroke. It can also leave more spent exhaust gas trapped inside the cylinder.
That residual exhaust occupies space that could otherwise contain fresh, oxygen-rich intake air during the next cycle. Gale Banks describes this effect as a form of “poor man’s EGR.”
The result can be reduced power and efficiency along with increased heat. From this perspective, back pressure itself is not beneficial. It is resistance the engine must overcome.
Back pressure can be created throughout the exhaust system, not just by the muffler.
Pipe diameter, bends, transitions, emissions equipment, and outlet conditions can all contribute. Through a bend, exhaust flow tends to crowd toward one side of the tubing rather than using the entire cross-sectional area evenly. This effectively reduces available flow area and increases resistance.
The entire exhaust path therefore contributes to how much work the engine must perform to evacuate the cylinders.
On a turbocharged engine, one of the largest restrictions is the turbine itself.
The pressure immediately upstream of the turbine is commonly called drive pressure. Eric distinguishes this from the broader term back pressure, which can describe resistance elsewhere in the exhaust system.
The pressure difference between the turbine inlet and outlet drives the turbine wheel. Reducing pressure after the turbine increases the available pressure differential while also helping reduce pressure upstream.
Excessive turbine inlet pressure is undesirable because the piston must work against that pressure during the exhaust stroke.
Banks demonstrates the effect using a late-model 6.7L Ram equipped with a 5-inch Monster Exhaust.
On the 2020 Ram, turbine outlet pressure measured 9.2 PSI with the stock exhaust and 8.5 PSI with the Monster Exhaust, a reduction of 0.7 PSI.
More significantly, turbine inlet pressure dropped from 49.5 PSI to 45 PSI.
That means a relatively small reduction downstream corresponded with approximately 4.5 PSI less pressure at the turbine inlet, reducing the pressure the engine had to overcome during the exhaust stroke.
Eric traces part of the “engines need back pressure” myth to restrictive aftermarket mufflers sold decades ago.
When certain exhaust modifications hurt performance, the explanation sometimes became that engines required a little back pressure. Repetition allowed that idea to persist even though restriction itself was not providing the performance benefit.
If changing an exhaust system hurts power, the actual cause may instead involve factors such as exhaust velocity, pulse behavior, runner dimensions, or scavenging.
Scavenging and back pressure are not the same thing.
Exhaust leaves each cylinder in pulses. With properly designed headers, those pulses and their associated pressure waves can help evacuate another cylinder.
Production log-style manifolds generally prioritize packaging, durability, and manufacturing simplicity rather than optimized pulse behavior. A properly designed header can instead use runner dimensions and collector geometry to take advantage of those pulses.
When changing exhaust dimensions moves the scavenging effect outside the engine’s useful RPM range, performance can suffer. That does not mean the engine needed restriction. It means the exhaust system was no longer properly tuned for the application.
Eric compares a stock-style Jeep 4.0L header arrangement with a Banks design.
The Banks header brings the runners together at a common collector to better manage exhaust pulses and promote scavenging. Runner length and diameter influence where that scavenging effect occurs within the RPM range.
Banks also applies scavenging principles farther downstream. Its exhaust-tip design is described as generating a low-pressure region at the outlet that helps draw exhaust from the pipe rather than adding restriction.
The central message is simple: back pressure is not the goal.
Reducing unnecessary exhaust restriction decreases the work required during the exhaust stroke and reduces parasitic losses. Where scavenging is possible, performance comes from properly managing exhaust pulses, runner dimensions, collectors, and flow behavior.
The distinction is critical: restriction creates back pressure; properly engineered exhaust geometry creates scavenging.
