Jeep 4.0 1991-1999 down pipe Mod.

[streetxj]

I'm going to an exhaust shop tomorrow to replace my dynomax super turbo muffler with a Aero 2525 turbine muffler. My current one is too quiet for my taste. While I'm there, I'm thinking about replacing the smaller diameter section of the down pipe with a 2.25 inch diameter one. The pinch was removed, but I've noticed that the pipe around the first bend and o2 sensor looks very small. Looks like 2 inches or maybe less. Then it expands suddenly to 2.25 to 2.5 at the half way mark. Will it be worth spending extra $$$ to install a 2.25 inch pipe from the header to the point where the down pipe becomes 2.5 inches?

Thanks

It's a 1996 jeep cherokee 2x4. Mods are 2003 4.0 intake manifold with thermotec heat shield, 62mm throttle body, 180 degree thermostat, Accel cap and rotor with taylor thundervolt 8.2mm ignition wires, high flow cat, with high flow catback exhaust, and modified stock intake system with K&N panel filter.

 

[gradon]

I'm 2.25" to the muffler where it changes to 2.5". I think 2.5" from collector to tailpipe is a minimum for all modded 4.0s and strokers, and some might benefit from larger than 2.5".

 

[Dr. Dyno]

Will it be worth spending extra $$$ to install a 2.25 inch pipe from the header to the point where the down pipe becomes 2.5 inches?

Definitely yes. A 2.25" pipe would be good but a 2.5" pipe would be even better.

 

[O-Gauge Steamer]

I run 2.5". Works for me. You can find more info here: http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/

 

[streetxj]

Thanks guys! I left my stock 96' 4.0 down pipe alone. The pinch was removed the first time I had exhaust work done to my XJ. It sounds awesome with the aero turbine muffler. Sounds deep like a flowmaster. The down pipe diameter matches the outlet diameter of the stock header all the way to the mid point of the down pipe where it converts to a 2 1/2 inch pipe all the way to the cat. My high flow cat is 2 1/2 inch inlet/outlet and the aero turbine muffler is also 2 1/2 inch inlet/outlet. This muffler is much closer to the cat than the dynomax muffler was due to some modifications they had to make for it to work with the dynomax 2.25 inch tail pipe. The Aero was linear instead of offset like the super turbo muffler. The pipe that connects the outlet of the muffler to the tail pipe is 2.5 inches which smoothly reduces to 2.25 inch (tailpipe). The stainless exhaust tip is 2.5 inches.

 

[CobraMarty]

Ordered a 2.5" high flow cat and this week to the muffler shop for a 2.5" SS downpipe to cat and then to 2.5" Magnaflow muffler and tailpipe. Smashed and cracked stock downpipe last time out at Rausch. Finall to get rid of that restrictive stock downpipe.