I am bringing my 06' 5.7 in tommorow morning to have the exhaust done. I have the Magnaflow Y Pipe and my plan is to run 3" from the Y Pipe to a single 3" Inlet, Dual 2.5" Outlet turbo muffler and then run the tips out the passenger side before the rear wheel. I do not have headers and have no plans to ever add them. And i will never be removing my cats.

This is a shop that does only exhaust and the manager was concerned that having a 3" exhaust with MDS may cause back pressure issues. In other words, the exhaust will have too little back pressure. But if MDS is only operating on the highway and at low RPM's, he thinks maybe it will be OK. He is basing this off the issues with putting a 3" exhaust on a 4 cylinder car. He says that causes major problems.

Will i be OK with a set up like this?

Lastly, due to the annoying sounds associated with MDS on the highway some people have complained about, he suggested going with a Turbo type muffler as opposed to one of the more free flowing types. Anybody agree?

I actually prefer an exhaust that only gets super loud when i get on it. At idle and driving around town, i prefer a more quiet exhaust.

 

Your running a 3" stock system now!
I left the resonator just after the y pipe in and have an 18" Magnaflow 3" center in 3" offset out duel chrome tips out before the right rear.
Sounds nice at idle and around town very little MDS drone. It may be worse without at least one resonator in
Back pressure shouldn't be an issue if you have it done this way.

 

I agree with the shop, you will have back pressure issues. Dynomax has a muffler with a damper installed to controll the drone, and you'd be just fine with 2.5" exhaust.

 

So you are saying put the Magnaflow Y Pipe in but keep one of the stock resonators?

I would think a turbo muffler would have more then enough back pressure to make up for the loss of the resonators.

I would really like to have everything new from the cats back.

 

What I'm saying is the resonators are there to offset the drone when in MDS. Take both of them off and I don't care what Muffler you put in you will get that annoying "helicopter flyin under water" drone. I would leave it in cuz you can always take it out later if you get a tuner and disable the MDS.
Also make sure to save your tail pipe w/resonator they are worth $ to someone who wants to go back to stock.

 

Your stock exhaust is 2.25 at the front of the y going into a 3 inch pipe you will be fine with the set up you are planning on running. If your worried about the mds my not get a programmer and disable it alot of people claims the get better mileage with it off plus with the programmer you gain some performance

 

I know you can shut the MDS off, but the issue is i don't want to. More then 80% of my driving is highway where the MDS makes a difference. And what little performance you gain with MDS off is (in my opinion) not worth it vs the fuel savings. My truck has more power then i would ever need as it is. So i have no desire to do any mods that hurt fuel economy.

I guess my issue now is just deciding whether i NEED to keep a resonator pre muffler or not. If it's a noise issue thats one thing. My concern is causing issues with fuel economy and/or actually causing harm to my engine/emissions system by having too little backpressure.

 

Well i just got off the phone with an Engine builder (builds race engines) who is a friend of a friend and he put my fears of too little back pressure to rest.

With a modern engine with O2 sensors and MAP/MAF EFI control you will not cause any sort of engine damage with too little backpressure. That issue was when you ran carbs which had no way to compensate automatically for a decrease in back pressure. If you put a super high flow exhaust in a car with a carb that was jetted to work with a certain amount of backpressure you could end up with a lean condition that could damage exhaust valves over time.

He pointed out that with stock exhaust manifolds AND cats, their will still be plenty of backpressure anyhow.

An article he refered me to as well was pretty interesting:

http://www.uucmotorwerks.com/html_pr...torquemyth.htm

 

Exhaust is done.

Left the front Resonator in place and went with a stainless free flow type muffler 3" Inlet, dual 2.5" outlet, tips out the side before the rear wheel.

You can hear the MDS when it kicks in, but it's not loud and with the radio at even a low volume you cannot hear it at all. Even though i brought the Magnaflow Y pipe to the shop, we opted to not use it as the shop said with stock manifolds and no other performance mods, it would be a waste of time to even bother installing it.