Originally Posted By: eljefino
Why bring exhaust pipes into this? They have no throttles.
I know you are intentionally being an [censored] for whatever reason, but there is a HUGE difference between the column of air flowing through the intake tubing, which is being REGULATED by the throttle body before it is able to go inside the plenum and the engine's exhaust system.
The TB, in conjunction with load, controls the amount of VACUUM that exists within that body (plenum) that the cylinders draw from. This is why I feel that the pipe sizing in FRONT of the TB (remember, I am NOT downplaying the role of ANY of the components BEHIND the TB), unless imposing a significant restriction, is not instrumental in whether the engine makes decent low-end power or not. On the other hand, plenum FILL is controlled by the TB, which is why I agree with the point mechanix made about TB sizing.
The exhaust SYSTEM, if properly designed will help an engine make MORE power. This is why long-tubed headers exist, tri-Y's, H and X pipes. Scavenging, collector diameter and length... these are all things that racers play with in order to get more power out of their combo. And I'm not talking some one-run K&N 5HP gain, I'm talking 20+HP through much of the engine's power band verifiable via multiple runs and reduced ET and increased MPH.
Look at it this way: The more air you can move through an engine, the more power it is going to make. The intake tract is REGULATED by the throttle body. It has to be for reasons I should not have to explain. Everything BEHIND the throttle body has to be tuned and optimized for the engine's intended use. This includes the exhaust system. Camshaft design plays a key role here too. The throttle body is the gateway to this entire system.
If you could control low-end torque by simply changing the airflow through the piping in FRONT of the throttle body, do you not think OEM's would do that? Rather than implementing much more complex systems like IMRC to control runner length and modulate low-end torque production and high-end output?
Instead of making sarcastic jabs at me, perhaps try to enlighten me as to why you disagree with my logic?
I have spent a lot of time researching and thinking about this stuff because I am into drag racing. But the cars we drive are also driven on the street regularly, hence the term street/strip. The goal is always to retain good streetability while getting the most out of a given combo.
Having a camshaft optimized for a given setup in conjunction with a good tune ultimately yields the best of both worlds. This is one of the topics we have beat to death on SBFTech.