Cat Back Exhausts

[gargantua]

Your car sounds cool munkeyboy, I want mine to sound like that.

[scathing]

i agree with scathing on this one.

its not about backpressure, backpressure by definition is a restriction and causes a loss of power.

Here's a response I prepared earlier.

And the "pulse tuning reversion" is also called "scavenging".

[Rolls]

What bout NA rota's,

NA rotors actually hate backpressure, you will see the most power running no exhaust at all. They commonly use full 3" systems on big ported NA rotors.

[mokompri]

Here's a response I prepared earlier.

And the "pulse tuning reversion" is also called "scavenging".

i have some disagreements with what you have written in that post.

you have noted that narrower pipes have less turbulent airflow then a larger one for low amounts of airflow. while this is true, and it has to do with gas velocities, more turbulent airflow doesnt necessarily mean more backpressure as you have stated.

another member in that post also noted that a high velocity exhaust system is desirable. the misconception here is that gas speed is desirable, where it is infact a side affect of other factors. laminar flow occurs when there is enough gas speed in a given pipe. for example 100cfm through a 2" pipe might give turbulent flow, but when we reach say 200cfm flow for the same 2" pipe it may give us laminar flow. this increase in mass of gas (keeping temp variable constant) going through the same pipe increases the gas velocities, and the reason for the increase of velocities is because of pressure buildup within the pipe, and this pressure buildup is back pressure.

if we increase the pipe to 3" and pump the same 200cfm through the pipe, gas velocities will decrease, which means less pressure build up, and less backpressure - and at the same time the flow may be turbulent again as its slower moving. this is why the bigger is better applies to turbo cars for less backpressure and if you want minimum backpressure for NA's - gas dynamics dont change, you still go for bigger. but of course if your not getting any backpressure at 2.5", increasing to 3" wont do anything for you.

that instance of turbulent flow is not an issue, its mearly a side affect. turbulence becomes a problem when it exists in parts of a laminar flowing system. for example you have a 2" pipe flowing 200cfm in a laminar fashion, the pipe has a flap inside it half way down the pipe. this flap is an obstruction to flow and causes turbulence around that area. the introduction of turbulence in laminar flow is what causes a loss of flow, not when the flow is turbulent simply because of a lack of gas speed.

[Eug]

volumetic vacuum