I really want to cut the stock exhaust off because I'm not ready to purchase what I want. I only use the truck on occasions and miss the sound of a true Exhaust. I was wanting to cut it before it hits the cat and the other thingy down. I was going to put a angled tip to blow it down. Besides being loud and making the 6.0 look bad. I'm also in the process of fixing rust issues and painting the undercarriage. I'm sure it's going to a very terrible droning and exhaust will be smelled, as the cut on the exhaust would be about 2ft after the exhaust levels out. what's the negatives? And does anyone know the diameter of the exhaust coming off the turbo?

 

Cutting it off before the cat is going make it drone, horribly I would dare bet. Not to mention the fact you run the risk of CO2 making its way into the cab and killing any other occupants.

I think that might be a negative

 

I would definitely not do that...


I've realized this myself and even after talking to some of the engineers behind the programming and design of the 6.0, there is some serious science behind the design of the exhaust system of your truck.


Contrary to what's been posted on the boards, the 6.0 does indeed need backpressure to run properly. How else are you going to properly spool the turbo?


If you cut the exhaust where you plan cutting it, you're going to disrupt the proper flow of exhaust and while the truck will sound cool, the turbo won't spool like it should and it will actually throw off sensors related to boost and exhaust like the EBPS, EGR valve, and MAP sensor, will be off to compensate for the change in exhaust flow.


If you were to simply cut off the muffler or remove the cat while keeping the stock exhaust, it wouldn't cause too much of a change other than the muffler being gone.

 

I just cut the cat and muffler replacing with straight pipes from riff raff. I thing it sounds great and increased my mileage. No problems so far.

 

Cutting the muffler and cat, help, hacking up the exhaust is what hurts,

 

Thanks for ruining a wonderful idea. I didn't think of the back pressure, but makes sense. Do you have any suggestions of how much I can cut off of the exhaust, because as my Ex is a work in progress, I would still like to drive it once in a while.

 

If I where you I'd just get a 4" back from the cat and get a cat delete pipe. It will be less headaches and you benefit from the open exhaust.

 

I just remember you talking about how your truck had immense Huevos and didn't want you to ruin that for yourself.

What Bill said^^^**

This is actually what I plan on doing with my current set up. I'm on the hunt for a stock down pipe as I type this. You can't beat the stock downpipe when it comes to spooling that turbo.

 

This is a 2 birds, one stone kind of deal. The exhaust needs to be out before I start that part of the rebuilt, but I need to work on the undercarriage before I buy the new exhaust. It's going to be alot easier to work on the undercarriage without a exhaust in the way.

 

Just take it off at the cat and down pipe. It will save you money in the long run.

 

If you're up for a civil debate, I completely disagree with this when we're talking about exhaust pipe, and will answer the question at the end.


Do you need exhaust pressure to spin the turbo? Yes absolutely, and that "back pressure" back to the engine is because the turbine offers resistance to the exhaust flowing through it, which increases as the compressor side is pushing more boost, which then requires more back pressure to spin the turbine.

Turbos work on Pressure Ratios....on both the compressor side and the turbine side. They flow X amount of air at a given efficiency at a Ratio of input pressure : discharge pressure somewhere on their map.


So how does that relate to why I disagree with the above that's bolded? Because you need "backpressure" before the turbo, but anything you can do to drop the backpressure after the turbo in your exhaust piping does nothing but help it to spool quicker and flow more by dropping the discharge pressure required for the exhaust to leave through the turbine. This helps the turbo, and in so your engine at every point in it's efficiency range.


The change in exhaust flow after the turbo doesn't do anything to hurt the EBPS, nor the EGR valve because those are all pre-turbo and the actual backpressure doesn't change, because EBP is the required value in the tuning. The tuning wants to see "X" EBP at a given RPM and throttle position/EGR position, etc. and moves the vanes to compensate, and boost is the byproduct.


As a final thought though, I agree with you guys on the rest of it.......don't cut your pipe......you undercarriage then becomes covered in soot, and there's the CO sickness to worry about. And the exhaust flange on the turbo is about 4", though many kits on the market only give you a 3.5" DP.

 

What exhaust mods reduce EGT?

 

Well I think your theory is wrong on back pressure,I've proven on my truck that it doesn't always ring true. I had a 4 in down pipe on my truck ,lost power and fuel economy,put the 3.5 down pipe on and gained all back plus. I know plenty of others that have had the same experience. Not all trucks react the same to mods. Sometimes it's trail and error.

 

The more efficiently and easily you can get air in and out of your engine, the lower your EGTs will be at the same fuel level. Some mods aren't that useful because the stock system is very good in it's form from the factory...but in general exhaust and intake are the two places everybody starts.

 

Can I ask did you test the power loss with a dyno and/or track times? Or just using the butt-dyno? Did you have a full 4" system and you were just changing the DP?