exhaust under load

Sorry, been gone for a couple of days. On a naturally aspirated engine, of which there are almost none in trucks, as the engine speed increases, the amount of airflow also increases because as the engine turns faster, the amount of vacuum in the intake manifold increases. At a higher level of vacuum, more air is pulled through. This increases wth rpm, until it stabilizes because the airflow has reached the maximum it can pass through the intake passages, or some other factor limits it. Remember helping dad as a kid and having to hold your hand over a carb to help choke the engine? Remember the amount of suction? With rpm, that suction increases until it reaches it's maximum flow.

And again, you have increased flow through the exhaust pipe at higher rpm, resulting in the gases exiting faster, and more shear between the moving flow and the stationary air surrounding it.

 

Residual-Leftover. Aint nuttin leftover in my pipes!

 

my thoughts would be that at 1500 rpm the engine is pumping in just enough fuel to run smoothe and safe while in neutral,under load at the samme rpm i would think the engine has to draw in more fuel and more air to keep running at that rpm meaning more fuel and larger explosions during the power stroke being louder.that's like hammering a brad into balsa wood then hammering a railroad spike into a tree with a 16oz hammer.you may swing every 3 seconds on each but you really have to work harder to drive that rail spike into the tree making a lot more noise for the same basic result.That's all I can come up with ya'll