I have been thinking about adding an exhaust system to my 04. I was wondering how much a new system helps the truck versus the stock system.

I guess my main question is how bad is the LLY exhaust in the first place? I thought I remembered they made some improvements to the exhaust (larger or mandrel bent or something) to the LLY that the LB7 did not have...am I correct?

There have been no significant changes to the exhaust system from the 4 bolt mounting flange back, between LB7 and LLY trucks.
So there is room for improvement in flow.
Although there have been several changes from the turbo to the same flange, some have a pre cat and and Cat.
We have torn off a host of the cat back sections already and replace them with the Banks stainless.
Removing the cat for on road use is a federal offense, and when removed for off road use it has been causing check engine lites to pop on, setting 0401 and 0404 egr codes.

Gettin all the emissions crap off(kitty,muffler) not only helps em breathe, the sound is a heck of a lot better. I think its worth it.

Definite gain on my truck. 15RWHP solid. Posted dyno plot in thread titled "where's the torque" or something like that...

Like Ted said, cat removal can cause codes on some trucks. It's also illegal;)

Ok, that answers a lot of questions. For some reason I though the exhaust was improved on the LLY.

Are most systems pretty much the same as far as power gains, with the main differences being in design, install, and sound? Or is there a wide variance in the actual power gains?

Also what is the difference in 409 and 304 stainless steel? I assume one is less likely to rust? What is the factory system made of?

Cat back, I didnt think it made a bit of a difference. Sounds dang close to stock (with the exception of startup). Mileage is the same, performace is the same, etc. The stock system is 3.5 inches and most aftermarkets are 4 inhces. Looking at them side by side, the ammount of difference in size is not much. I was pretty disappointed when I got mine installed.

May I assume these numbers are sans kitty (for testing purposes only, of course ;) ).



Definite gain on my truck. 15RWHP solid. Posted dyno plot in thread titled "where's the torque" or something like that...

Like Ted said, cat removal can cause codes on some trucks. It's also illegal;)

Materials of the OE systems are: 400 grade stainless up to muffler, then aluminized. The 400 grade SS will rust. Aluminized willremain silver for a LONG time. 300 grade SS is like a kitchen sink or stainless appliance.

My dyno testing was w/o cat...

only if you do the whole pipe. IE cat gone

I got about a 100 degree temp drop on my EGT's at 70 MPH on the Freeway with a CAT back 4 inch system and the Juice on level 3, or at least that's what the Attitude says. It will also run further into the fourth/fifth shift point before temp limiting on level four with the Juice. I don't run mine in level 5 so I can't say anything about that. Bear in mind that this is not a scientific comparison, but the bigger exhaust seems to have helped mine in the EGT area.

If you research this you will find the results will be very little improvement if any in performance with stock trucks. EGTs are reported to be about 100° lower though, so if you pull with a power box I would consider the whole exaust.
Not worth the money untill you are adding some high horspower boxes IMO.
For the record, I gained no ETs by adding my Flowmaster muffler while using a 125 hot juice. ETs the same before and after the muffler. Sounds great though.

Its worth it IMO , sounds better , spools alittle quicker, and egt temp drop. 4" turbo back though if your gonna do it !

How are you guys dealing with the P0404 and P0401 codes (if you get them) when removing the CAT?

VERY nice difference to drive on my 2005! The difference seemed more subtle on my 2002, but I drove it very little with the stock exhaust as was the case with my 2005. I have a 2004 LB7 due in for exhaust soon and we'll see how that one does...

BMDMAX had a post with sound clips here as well...

You will see better results on an LLY than someone with a LB7 would.
Getting rid of the cat was by far the biggest reason for me to do the exhaust.
I don't have flow tests, But I would imagine that the Cat is more restrictive than the muffler. With that in mind I wouldn't spend the money for a cat back, while leaving the bigger restriction in place.

I have my Cat pipe ready to go back in anytime I need an emissions test. (Once every 2 years) It really looks best right there on the garage floor where it belongs.:D
No check engine light because my truck has "Federal emissions".

BTW My dealership service department doesn't care weather the Cat is in or out. They also don't care that I unplugged the EGR. It may be a good Idea to talk with your service advisor and make sure they are cool.

Dont look at exhaust/intakes for power. Look at it to lower EGT's so you add more power.......you get the power/milage (Not in all cases) as a side effect.

DGM

Afternoon,

We see the same HP and TQ gains and EGT losses as we always have on the LB7 or LLY with the MBRP exhaust we sell and our customers installs report the same as well.

Mark @ DPPI

Mark, I saw a 90ftlb increase on one dyno run on an LLY with an exhaust change. Can you confirm this. Thanx Geo.

I started with the AFE stage 2, Then I went with the Banks exhaust 4", I purchased the Banks Six-Gun and Speed loader-hasn't been delivered yet. So far improvements are noticeable. I feel like the truck has better response, and I am sure the temps have been reduced.

With a 4" straight pipe, I dyno'd 271rwhp on a Mustang. No intake mods, stock tune, no harness box. There is zero doubt in my mind that the exhaust is worth a sizeable gain, nearly 10%.