Formula 1 cars run with as little back pressure as possible. Why? Back pressure is not needed to make power. Proper scavenging of exhaust gases is. Why doesn't F1 use exhaust valves? Rules. But there is more to it. Look at the intricate piping for exhaust:
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For street and motorcycle use, the exup or SET valve (suzuki) is used to modulate scavenging on exhaust that are limited by space to simple design. They don't create backpressure, they shorten header length with the sonic feedback in the flowing gases. These valves also help in cutting down noise and passing strict EU noise laws.
Back pressure does not create power. Period. It moves the torque curve around. Yes, this can be optimized to a specific engine's needs, but the scavenging aspect of a properly designed exhaust is FAR more important.
Now remember power is torque per second. So if you make the same torque but just in a different spot, you make no extra power. Unless some magical valve (impossible) can push the peak torque to 14000 rpm.
So an engine with no exhaust valve has a static torque curve that must be optimized with exhaust cam timing. This CAN affect scavenging and must be carefully designed to maximize both with no hinderences. If you have a valve, you can free the camshaft to exploit the scavenging to it's fullest.
Watch CART, NASCAR, F1, Moto Gp and if you hear of a retirement from a broken exhaust header it's due to no power from no scavenging and exiting hot gases most likely somewhere it will cause fire.
Scavenging?
It empties the exhaust chamber as much as possibly to increase the vacuum for more intake charge. It runs cooler so denser more powerful air can be exploded in the compression stroke. This is needed since most engines have a small exhaust valve to balance exhaust gas speed and reducing temps from the pressure drop across the valve.
For street and motorcycle use, the exup or SET valve (suzuki) is used to modulate scavenging on exhaust that are limited by space to simple design. They don't create backpressure, they shorten header length with the sonic feedback in the flowing gases. These valves also help in cutting down noise and passing strict EU noise laws.
Back pressure does not create power. Period. It moves the torque curve around. Yes, this can be optimized to a specific engine's needs, but the scavenging aspect of a properly designed exhaust is FAR more important.
Now remember power is torque per second. So if you make the same torque but just in a different spot, you make no extra power. Unless some magical valve (impossible) can push the peak torque to 14000 rpm.
So an engine with no exhaust valve has a static torque curve that must be optimized with exhaust cam timing. This CAN affect scavenging and must be carefully designed to maximize both with no hinderences. If you have a valve, you can free the camshaft to exploit the scavenging to it's fullest.
Watch CART, NASCAR, F1, Moto Gp and if you hear of a retirement from a broken exhaust header it's due to no power from no scavenging and exiting hot gases most likely somewhere it will cause fire.
Scavenging?
It empties the exhaust chamber as much as possibly to increase the vacuum for more intake charge. It runs cooler so denser more powerful air can be exploded in the compression stroke. This is needed since most engines have a small exhaust valve to balance exhaust gas speed and reducing temps from the pressure drop across the valve.
