2003 Excursion 6.0

Ok, so I still have my cat on, did a muffler delete about a year and half ago, sounds better! I dont want it to loud since it is a SUV. Will removing the cat make it that much louder? We dont have testing here in Columbus Ohio.

secondly, I have 280k on the odometer. My old Expeditions cats went bad around 220k, one got loose inside and turned sideways which clogged the pipe... are diesel cats the same as gas ones? I dont want to have to worry about it clogging or having issues with it, especially when towing! That would be very bad!

I've thought about taking the cat off and putting a muffler back on it, so it isnt to loud/resonating inside the cab of it. Thoughts? What have you guys done?

yes I know I only have one O2 sensor before the cat... nothing after.

 

What on earth would a diesel be using an O2 sensor for?

Diesel's don't control fueling based on oxygen content or lean/rich fuel mixture ratios.
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Exactly.

And, no, it's not likely you'll know a difference in sound if you have a muffler. It is entirely possible that the cat is plugging up the flow a bit.

I ran a 4" straight pipe on mine for a long time before the Cummins Swap, and it was certainly loud. The whistle would hurt my ears under a bridge or close to a wall. But, I liked it so no worries on my part.

 

Oh, as far as sound goes, I knew a guy that had a cat delete pipe on his 6.0 (ebay piece if I remember correctly), with the stock muffler behind it. His truck didn't sound or smell any different before or after that I recall.
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The exhaust should smell different. That's why the cat is there. The cat also serves other purposes:

-It creates back pressure to spool the turbo

-It also a sound deadener for the turbo up front. Without it there, you can hear the turbo whining as it spoils. On some of the early 2003 trucks, there's an another type of sound deadener in addition to the cat. It's either built into the downpipe or near it.

So aside from omissions, this is the purpose it serves.

 

Back pressure is the enemy of spool up. Saying "it creates back pressure to spool the turbo", is a gross conceptual error and just a plane silly statement to make.

The ONLY purpose the cat serves is emissions (not omissions), the sound quieting is a side effect.
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I was trying to find where this was mentioned, but it may have been when I spoke with one of the engineers who were there during the development of the 6.0. JMaksew mentioned it somewhere.

Regardless, I've driven and built plenty of stock and even non-stock trucks and the stock ones run hard even with the cat in place. I'm working on one now that I have to stud and reseal. He wants the cat deleted and the muffler cut out for a straight through. I'll see how it runs stock.

Maybe you could explain why even with hot tunes and a healthy engine there is turbo lag with a 4 inch down pipe.

 

Now I'm very curious? With or without the cat, what's better? I dont want it to loud, dont want to **** my wife off its to loud, we pull our camper alot with the Excursion. What's the loudness between just having the muffler or just having the cat? Does anyone know? I can hear my turbo alot without my muffler. Just sitting in the driveway I can hear it spool when warming up.

 

​​​​​​​Sure, turbo lag is caused by the resistance of mass to acceleration.
Hence the reason small turbos spoil faster.

The driving force for the turbo is the differential pressure between the exhaust gas flow and atmosphere.

If you hold back pressure in the exhaust ( via a cat, baffled muffler, small pipe , etc) you lose some of that DP.

There a few other factors besides back pressure that can affect spool up ( pre boost fueling, turbine size, turbo housing ratio, variable vane position if so equipped, inlet air restriction, injection event timing,etc) but exhaust back pressure IS NEVER A GOOD THING FOR TURBO SPOOL

The biggest reason “ big” tunes can increase turbo lag is injection timing. The farther before TDC you set injection timing ( to a point ) the longer the fuel stays in the cylinder and the less energy it has coming out of the exhaust port so it spools the turbo slower. Putting an exhaust restriction behind that would make it even worse.

A good common rail tune would have lower injection timing at low RPM, (something like 15 degrees) and advance the injection timing in the upper RPM band ( to something like 24 degrees). Then you wouldn’t have as much lag running the “ big “ tune but you still be able to make the higher RPM power.
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Better is a personal preference. Loud to you may be different from what someone else considers loud, diesel smell may be intolerable to your wife, but not bother you, so "better" is a personal decision.

If you're driving on the street, the federal government say to have-to-have a cat to be legal.

From a performance standpoint (offroad use only of course), then there's no question, no cat is the way to go for engine performance. The downsides of not having a cat are being illegal for road use, smell, and noise.
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Now explain it with stock power and a 4 inch exhaust and then a mild tow tune with a 4 inch exhaust.

 

Explain what?

Are you still trying to justify / defend the ridiculous statement that exhaust back pressure helps with turbo spool? Basic (and I mean real basic) physics state otherwise. If you'll think about objectively for just a few seconds, I'm sure it'd make sense.

I get it that you read that statement somewhere and accepted it, but its simply not true. The only way you could say a given cat helps turbo spool is by comparing it to another, even more restrictive one. So if cat X was less restrictive than cat Y, then one could spin the dialog to say that cat X helps spool, but cat X would still be worse (and spool slower ) compared to no cat at all.
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For me it's about a different perspective. If I'm wrong, I'm wrong and willing to learn from it. This is why I asked you to explain the other two variables. If you don't know, you don't know but just because you argued my point and gave a lengthy matter of fact explanation, doesn't mean that I nor anyone else accept it as fact. It's your opinion and you're entitled to it.

You may or may not be right, but your cocky and arrogant attitude will guarantee that nobody listens to you.

Here on FTE, we learn from each other and treat each other with respect. If there's a difference of opinion, people compare notes and sort out their differences in a respectful manner. They don't impose their opinion just because they feel they're right.

So if I were you, I'd scale back the attitude and play nice like everybody else. Maybe we can learn something from each other.

 

I was/ am playing nice, even using nice words like "silly" vice words that have a better description but might be considered rude. And I disagree with one of your points, nothing I stated was opinion ( entitled to one or not) it is/ was physics fact. Take the facts as you choose to. If you still feel that a restrictive exhaust will help turbo spool, try doing an experiment of some kind to confirm your theory.
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See above, that's exactly what I planned on doing.

I'll also see how it runs with the 40 hp Tow tune.