Ive looked at a few catbacks like the atlp quad and the xlr8 and ive noticed that they take the 2.5 tube and split them into 2.25. Why is this? Wouldnt it be more beneficial to just keep 2.5 throughout the whole system? Im trying to find info on the CT exhaust is it 2.5 to 2.5 or 2.5 to 2.25?

 

Not having seen the systems in person, I'm assuming you mean why the J-pipe is 2.5" and after the muffler its 2.25". There needs to be a fine balance between the back pressure and exhaust scavenging effect. Bigger is not better.

Exhaust systems are in reality are very complicated performance parts to tune properly to extract the most power while keeping their legality, and in addition to that it has to sound good too. I'm no engineer, so maybe someone else can chime in with more detail.... but rest assured they did it for a reason. I wouldn't be surprised if they changed it after the muffler to 2.5" and it actually lost power vs. 2.25"

 

So will you find that most catbacks end up starting from 2.5 and ending at 2.25?

 

No need to keep it 2.5 per side once it splits. Remember its splitting in to two 2.25....whats 2.25 X 2..... last I remember should be 4.5 so its not really necessary to split it to 2.5 to both sides all the way back.

 

Makes sense.

 

My experience: I had the Greddy EVO2 along with Pro-cats, RV6 J-pipe and test pipe. I had mad power on top end, but very low end power (even less than stock). I changed the mufflers to 2.25 Borla's; everything balanced out very nicely.

So dropping from 2.5 to 2.25 in the piping does serve it's purpose.

 

when splitting in 2, 2 outlets of 2.25 outflow one 2.5" pipe. There is no need to keep it 2.5. When you go to 2.25 it helps with backpressure and helps keep some low end torque. It's not exactly 2x's but close. 2 2.25" will flow the same as about 1 4" roughly.

 

^ Best answer

 

Cross section of a 2.5" diameter pipe is 4.9sqin (1/2 diam)^2 x PI. Cross section of 2.25" diameter pipe is 3.9sqin, but remember there are of them, so combined cross section of 2 x 2.25" dia pipes is 7.8sqin, way more than the cross section of a single 2.5" pipe.

Two 2" diameter pipes, with combined cross section of 6.3sqin will still, in theory, flow more than a single 2.5" diameter pipe, at 4.9sqin.

 

so many numbers that the newbs would