Took it to my exhaust guru with the initial plans to go 3" all the way from the down pipe. But according to him not worth it, with the restrictions out of the system the factory madrel bends flow equialent to a custom bent 2 and 3/4. One of the biggest restrictions is right before the factory flex pipe where it necks down to nearly 2", then the cat and of course the fridge sized muffler. I went with a true 2.5 inch flex pipe and a magnaflow muffler and love the turbo whistle now, and just a slight edge to the exhaust note to remind you of the $400 you spent.

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2006 Jeep Liberty Limited CRD - DRL's activated, Moab wheels and 215/85/16 Goodyear Duratracs, Frankenlifted, Cummins Lift pump, Magnaflow 2.5" all the way back, no cat , suncoast, Viper command start, Valentine One.
1967 Jeep M725 - a real cream puff

Wow, that's a chunk of change! I paid $120 for the Flowmaster and $15 for the extra 2 1/2 exhaust pipe. Total of $135 and that includes the "Free" hollowed out cat that I picked up at a muffler shop.
I have all the original stuff ready to go back in if I have to (or when I get done "Testing").

I think the point is that getting the exhaust flowing is better than stock does help about 8% from what I have seen.

the true 2.5inch flex pipe was 100 bucks, you did the install yourself, and I live in Canada we get hosed on everything.

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2006 Jeep Liberty Limited CRD - DRL's activated, Moab wheels and 215/85/16 Goodyear Duratracs, Frankenlifted, Cummins Lift pump, Magnaflow 2.5" all the way back, no cat , suncoast, Viper command start, Valentine One.
1967 Jeep M725 - a real cream puff

2.5" custom install for $100, not so bad.

The Cummins diesel with 5.9 liters and a 5" pipe has an area of pi x radius x radius = 16.25 sq inch
A VM 2.8 liter and a 3" pipe with an area of pi x radius x radius = 7 sq inch.
A VM with 2.5" = 4.9 sq in
The 2.8/5.9 = .47, 7sq inch/16.25 sq inch = .43 Or 2.5/3" is 4.9/7= .7 or 70% of the area of a 3" pipe to blow through!
Therefore my idea of a 3" pipe is not quite what a Cummins 5.9 with a 5" pipe is blowing through.
If I did not have such competition for the mods with my wife's money I would have a 3" all the way now!!!

R

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'06 Jeep Liberty Sport CRD with: GDE Hot Flash and Tranny Flash, ehm, Cummins fuel pump, 3" Magnaflow muff, Moog K3199's, Skids, 225-75-16 10 ply, OME springs, Euro T/C, Shift kit, Trans cooler w/thermal bypass, Bigboy bkt, Samco CAC, Brake controller, Trans temp gauge, Al's Upper Arms

So after reading this thread I still am unsure of which setup is best? Ideal setup, which should I do?

Thanks!

It depends.
Some have 3" like me and I am going to tow. Looking to go 3" all the way.
Some say 2 1/2" is all you need, maybe so.
There are sections of pipe 2 1/4."
The key to lack of performance is the cat. Somehow the innards fall out with a 1/2-3/4" rod driven into the core, 2-3 mpg gain some say.
Some would go with a 3" cat, some would hollow it out.
My 18" Magnaflow is a little loud for my liking, might have gone a little longer though.

R

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'06 Jeep Liberty Sport CRD with: GDE Hot Flash and Tranny Flash, ehm, Cummins fuel pump, 3" Magnaflow muff, Moog K3199's, Skids, 225-75-16 10 ply, OME springs, Euro T/C, Shift kit, Trans cooler w/thermal bypass, Bigboy bkt, Samco CAC, Brake controller, Trans temp gauge, Al's Upper Arms

I just installed a 2525xl. I immediatly noticed less turbo lag. It takes off like the MAF is unplugged. It has a deeper rumble to it, no drone on the highway but a little more vibration in the seat and pedal. It wasn't easy to weld either. I used 308l wire. I think my milage went up too. I'm happy.

Well i have been reading all the articles and I went with the straight pipe no muffler. I sure like the sound and the coasting when the foot is removed from the throttle its a fuel saver.

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2005 CRD Sport 4x4
EHM,ORM,Straight pipe exhaust,Facet 40109 lift pump