3" catbacks compared to "true" 3" catbacks. How much hp difference is there?

[-DSM2NR-]

There are some catbacks that go from 2.5" (testpipe) to 3" and then end at 2.5" at the muffler.

My question is. How much hp gain is there with these catbacks compared to stock catbacks? And how much more hp does a true 3" all the way through catback give compared to these "fake???" 3" catabacks?

 

[Acinonyx]

Depends on the application.. Honestly I didn't notice much of a difference between a 2.5 inch/3 with bottlenecks and a true 3 inch system... And my customers cars were running from 16-19 psi boost... the true 3 inch system seems to have a different sound, that's about all I notice. Bottom line - I have yet to see Dyno Proven results with a 3 inch, I'd think it'd only be useful on insane applications. Unless you are running one huge turbo, don't waste the dough.

 

[JrRelic]

Your flow rate with that set up won't be all that different that 3" the whole length.

That 3" section is creating a low preasure area in the tail pipe. Drawing gas from the cat and into a cross sectional area of more than 30% greater. If the 3" dia section of pipe if of proper length it may generate a pulse that minimizes the 2.5" reduction at the end of the pipe. Creating a free flowing exhaust without the full 3" tail pipe.

 

[-DSM2NR-]

Your flow rate with that set up won't be all that different that 3" the whole length.

That 3" section is creating a low preasure area in the tail pipe. Drawing gas from the cat and into a cross sectional area of more than 30% greater. If the 3" dia section of pipe if of proper length it may generate a pulse that minimizes the 2.5" reduction at the end of the pipe. Creating a free flowing exhaust without the full 3" tail pipe.

Ummmm..........could you explain that in english please?

 

[kidwiththelaser]

Ummmm..........could you explain that in english please?

Im not positive, since I am not JrRelic.

But hes saying that it will be just as good.

 

[JrRelic]

That is what I am saying. If I remember correctly DSM's start to free flow with their exhaust between 2.5" - 3". Now, using the same principles as runner design. You have a mild restriction at the down stream end of the 3" DIA piping. The difference in pressure is enough to slow down the flow of exhaust. However, every time the valves open and close a pulse is generated. That pulse increases the pressure in the larger pipe and helps to push through the 2.5" pipe, to achieve a free flowing rate. Much the same way that the pulse helps to fill the cylinder in a N/A engine, when the intake runners are the proper length.