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Technical Info: 2nd Gen 24 VALVE DRIVETRAIN Technical discussion of second generation (1998 - 2002) 24-valve engine and drivetrain questions, solutions and upgrades.
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Old 04-25-2014
cali4niacoalroller cali4niacoalroller is offline
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Question Exhaust Diameter 4" or 5"

I remember when I was putting a 3" dual exhaust under my Mustang I had to increase the size according to the Hp I was hitting, but yet maintain a enough back pressure or start losing power. So I am guessing the same holds true for our Cummins exhaust. What's the max Hp that you should be pushing through a 4" exhaust before you should be considering stepping up to the 5"?

I was also thinking about running stacks, and was wondering if anyone had any pics of how they ran theirs under their beds with heat shields between the tank and tubing. I saw a system a while back that someone put on their rig that used square tubing under the bed and capped the ends 45* the bottom of those ends. The reason for this is because I just want the stacks up through the bed in the corners so I can put chromed expanded metal around them to keep things from melting. I don't want the one hole and this exhaust running across the inside of the front of my long box..... I know its done and just want to see if anyone else has done it...
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Old 04-25-2014
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Never did the stacks, so no help there.

But for the 4" exhaust max hp rating, 500 hp is about max., then go to 5".
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Old 04-26-2014
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You don't want back pressure on a diesel the more flow the better the turbo works.
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Old 04-26-2014
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An old mechanic once told me:

You get as much air in the front as you can ...
... and as much exhaust out the back !

The only bottle neck in that flow should only be the engine.
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Old 04-26-2014
cali4niacoalroller cali4niacoalroller is offline
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Ya, I heard that too..... I am leaning towards the 5" only because I like the deeper sound that it produces over the 4".... My parents motorhome has a cummins and it has a 5" exhaust and purr's like a kitten going down the road with a nice low drone..... But wasn't sure if that sound was because the exhaust tract is so short (diesel pusher) or because of the 5" and the muffler.....
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Old 04-26-2014
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I have the 5" with only a resonator and at certain speeds there is a slight low drone. Make sure it doesn't bother you before you invest. It doesn't bother me, but after having one, my friend said his was to much and went back to the 4".
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Old 04-26-2014
cali4niacoalroller cali4niacoalroller is offline
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Unfortunately none of my friends run Dodge's.... I know I do need new friends.... I would really like to hear the 4" vs 5", and Youtube is only helpful for so much.... Which is the main reason that I haven't even done a straight exhaust let alone the stacks that I like so much....
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Old 04-28-2014
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My 4" MBRP had a real drone at highway speeds with a muffler.
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Old 04-29-2014
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5" is very noisy and is complete overkill in my opinion. A good 4" turbo back will do just fine. Besides, unless you are running twins of a massive single you will need to consider adapter flanges and down pipes. Just my thoughts.
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Old 04-29-2014
cali4niacoalroller cali4niacoalroller is offline
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I will eventually get twins, but not sure if it will be this summer or not.... have to iron out a few things at the moment and if its a go, then its game on..... I am considering stacks on my dually, but want the crossover under the bed not through the front of it.... So still undecided.....
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