2.25 or 2.5" exhaust - bolt-on'ed 4.0

yossarian19 · May 19, 2013

I'm looking at cat-back systems for the '98 4.0 / aw4 / 231.
While "bigger is better" always has an appeal, my thinking is that while a larger exhaust is going to make better peak power that power will be way higher in RPM range than a slightly smaller exhaust would. So, with a 4.0 with just a handful of bolt-ons that rarely sees 3,500 RPM, I think the 2.25" cat back is going to get me the more noticeable gain & mileage increase, because it will keep gas velocity higher in the lower RPM range.
Sound correct?

Johnnie Walker · May 19, 2013

2.25 is what is factory after the cat. I would just go with that.

BADaXJ · May 19, 2013

I think 2.25" is the more functional choice, but in my opinion the gains are minimal and the 2.5" sounds better so I run a 2.5" on both of my XJ's.

cal · May 20, 2013

We asked this question to an industry leader as far as exhaust goes (Gale Banks). "Back pressure is BS, bigger is better.".

I ran 2.5 on my stock clapped out renix, and noticed better torque right away. Just do it.

adrenalinepirate · May 21, 2013

Made my own exhaust out of 2.5. Flowmaster with highflow cat. Go with the 2.5 sounds better, my old jeep was 2.25 dyno max muffler all the way out with new tubing. Way better sounding and performance with 2.5.

yossarian19 · May 22, 2013

I don't want any droning, at all. Which mufflers did you guys use & does it bug the piss out of you? My Flowmaster 40 @ 2.25 drives me crazy.

gradon · May 22, 2013

I recently put on the Borla Pro-XS 40358 2.5" muffler and it sounds pretty good when "on-the-pedal" and reasonable when not:
http://youtu.be/ZWnmSxmXqFw

raneil · May 22, 2013

yossarian19 said:
I don't want any droning, at all. Which mufflers did you guys use & does it bug the piss out of you? My Flowmaster 40 @ 2.25 drives me crazy.

I went with 2.5" all the way back and a Magnaflow cat. Started with the SpinTech Sportsman Street muffler (video), but decided it was too loud. Replaced it with a Magnaflow 11256 (video), and I like it better. Much smoother and more mellow.

gradon · May 22, 2013

I had a Magnaflow 13216 3-chamber before the Borla and it was a little louder and bassier than the Borla. I still have it if anyone's interested.

*89Laredo* · May 22, 2013

Where are you guys finding bolt on 2.5" mid pipes? Will they work on renix?

Johnnie Walker · May 22, 2013

yossarian19 said:
I don't want any droning, at all. Which mufflers did you guys use & does it bug the piss out of you? My Flowmaster 40 @ 2.25 drives me crazy.

Something that goes straight through.. Maggy, dynomax ultraflow, bullet proformance, etc. I have a 14" 4x9 maggy + turndown after it, and love how it sounds. If you want quieter, a longer/bigger body will be what you want.
I picked mine up a couple years ago on amazon for about 50$

2.25 or 2.5" exhaust - bolt-on'ed 4.0

yossarian19

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Johnnie Walker

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BADaXJ

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cal

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adrenalinepirate

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yossarian19

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gradon

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raneil

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gradon

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89Laredo

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Johnnie Walker

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