Just like a water hose, you will use your thumb to suppress the water hose to let the water spray out in a higher pressure. This is the same case as the "back-pressure" acted on the exhaust and engine. You suppress the exhaust air-flow, so that you gain low-end torque.
If you have a low-pressure water supply, but the water hose is so big that the water just flow out of it, rather than a rushing-spray motion. So, you loss your low-end torque.
If you have a high-pressure water pressure, you definitely wouldn't a small hose that will block the water flow. Because the "back-pressure" acted on your engine will cause loss of high-end torque and damage your engine in a long run. Thats why turbo engine needs a straight flow muffler with bigger diameter to gain the high-end torque and to achieve a higher boost from the exhaust.
Just my 2 cents and if theres any mistake in my theory, please correct me :)
If you have a low-pressure water supply, but the water hose is so big that the water just flow out of it, rather than a rushing-spray motion. So, you loss your low-end torque.
If you have a high-pressure water pressure, you definitely wouldn't a small hose that will block the water flow. Because the "back-pressure" acted on your engine will cause loss of high-end torque and damage your engine in a long run. Thats why turbo engine needs a straight flow muffler with bigger diameter to gain the high-end torque and to achieve a higher boost from the exhaust.
Just my 2 cents and if theres any mistake in my theory, please correct me :)