gilroy222

I haven't been able to find much on this topic because most people just do cat-back.

I had true dual (headers back) exhaust on my 5.3 sierra. I realise the downpipe on these cars makes it hard to do the same but I'm wondering if anyones done it? Is it possible to take out the downpipe and run the exhaust underneith in order to allow for true duals?

I'm going to talk to my exhaust guy next time i'm home but just thought i'd get some input. My truck had two highflow cats and two flowmasters so it was two pipes the entire way back so i'm wanting to do the same since he does all this for 800 bucks including the price of mufflers and cats. I'm also wondering about the resonator... leave it or remove it? I assume it's pretty restrictive but i've read that it helps with the car not sounding like sh*t in DOD mode. I would like to keep DOD mode and Lew has already said he can do two tunes for me... one with DOD and one without. If DOD is only going to be on during the highway or downhill I don't care... just can't have it turn to a fart cannon doing 20mph going through the small town that i'm from where v8's and trucks are much more popular than civics and things along those lines lol.

I should mention my exhaust guy does all custom stuff. So he can bend/make the tubes for any which way I need them to go. If I have to leave the downpipe does it matter if he makes a new better flowing one?

Jteske88

true duals seems hard to accomplish since we have the crossover pipe. unless you fabbed from that back, but then i think there will be space issues.

TheMonteMan

true duals have been done on a wbody before. ive only seen it once and it was a very very tight fit, and it wasnt an ls4 car. on the whole resonator thing i think dod sounds like **** the second the exhaust is any louder than the factory exhaust. it doesnt sound like a 4cylinder though it sounds like a helicopter. maybe the good ole boys will think thats cool(i dont).

91parkave

iTrader: (4)

you could make it happen im sure it would be similar to the 04 GTO exhaust which IMO is one of the best sounding factory exhausts ive ever heard. crossover pipe would be like any other v8 car that came with a y pipe, meaning one bank would have farther to go then the other. But after its all said and done we can up to 4' single which will support easily 800+WHP which im sure none of us will ever hit

Haulin_Ls4_GxP

iTrader: (1)

I would think in order to do it you would have to use some sort of x-pipe and install your front o2 sensor in it. I'm not to sure your going to be able to fit two cats in there also if a car comes from the factory with one cat I don't know that you can legally add another cat.

gilroy222

I've heard of this helicopter noise before in the truck forums. Anything that doesn't sound like a throaty v8 doesn't sound cool to me lol. And any video that anyone has ever done on DOD never turns out good enough to actually hear the DOD in action. How often does the DOD actually come on though? Too bad it wasn't like the Impalas that told you. Like I said if it's only on the highway I don't mind and if it does get that bad I'll put in Lew's NO DOD tune.

I should say though, i'm not only going for sound... the reason i'm so concerned with duals is for power. I want the exhaust to also flow the best I can get it to. Power is more important to me than sound so the mufflers are just an added bonus.

Resonators just seem like another restriction to me but this is the first vehicle I've owned with a resonator. I understand it's probably not the best to add a second cat. So I may just do the y-pipe thing then. Just so I can explain to my exhaust guy when I see him, where exactly is the resonator and cat located?

91parkave

iTrader: (4)

Full 3' split 2.5 rear and ull be good till about 375whp

lVloses

iTrader: (1)

^ This.

DavidGXP

iTrader: (14)

Well Dam!

91parkave

iTrader: (4)

Lol David this means you need dual 3' exhaust lol

gilroy222

So by this you mean 3' crossover/downpipe and then y-pipe to 2.5 the rest of the way back? I think that's what you mean so that just leaves me with Res/no Res?(If it will restrict airflow with that 3' or not)

He puts on custom universal highflow cats that are most comparible to the magnaflow ones. Then he does custom mufflers that are most comparible to Flowmaster 44's, if I remember correctly from when he did my truck.

Even though it's not true dual how much horse you figure i'd get realisticaly?

I need to have a cat, up here in Canada unless you have a truck and live on a farm you have to have one so I figure highflow is better than stock.

gilroy222

Oh and does anybody have a good quality sound clip of this "helicopter noise" with the DOD?

baltsk8er69

iTrader: (1)

No he means 3 inches from the header back then where it splits use 2.5 to the mufflers.

TheMonteMan

heres a video its not my car. crank up your volume. its not the greatest video of it, but you can hear it.


also i think these cars can sound plenty throaty with a resonator in place. i think either run a good resonator and no mufflers or no resonator and a nice pair of mufflers and the car sounds good.

to my knowledge dod only engages in 4th gear. at less than quarter pedal? not sure what speed thats at, but for the limited time i still ran it, it definitely would engage during city driving. below 40mph. im sure that the rpm or mph it engages at can be changed with a tune, but i would be concerned about oil consumption.

wow thats a big video!

91parkave

iTrader: (4)

Here's the sound clip And as other members clarified 3' downpipe and if I were u I would get a resonator they don't restrict flow generally but its better to have on a daily driver. Then mufflers of your choice and please just say no to flowmasters

gilroy222

Alright thanks guys. Ya I knew you meant a 3' downpipe but I must not of worded it correctly for clarification. To my understanding the down pipe is also the entire pipe that crosses over the engine bay from the front and down to where the exhaust splits right?

As for the resonator I guess i'll just see if he can cut the old one out of there and put it on the new exhaust.

Lastly, how come you don't like flowmasters? lol I love the sound of my truck with them but that is way different I guess. It's a lot older and no DOD or resonator. I'm afraid I may be limited as to what I can put on for mufflers because he'll give me a lot better price on his "flowmaster knock-offs" since he gets them at cost....same with the cats.

gilroy222

Did I read somewhere on here from another member that GM made a part to stop oil consumption and that the part was most likely already implemented into the 08's? If so mine is an 08 and although I haven't checked in a while the last time that I did the level looked fine.

baltsk8er69

iTrader: (1)

The downpipe only gos from the rear manifold to the resonator. Your including the crossover which is not part of the down pipe. And I've had flowmaster super44s for my last 3 SS' s and love them. Listen to all of them...everyone on this site hates flows for some reason I love them. Lets start the debate of how flows will cost you 1.7 horsepower. If that concerns you throw a type r sticker on your back window to off set the loss in power, And BAM your back in business.

GXP25

iTrader: (3)

No, the part was released in 2012.

gilroy222

lol it doesn't concern me a lot. I figure flow 40's or 44's are better flowing than stock. From the videos i've seen on youtube I don't mind the flowmasters really but if there's a better and cheaper muffler out there I'll get that instead to have the guy put on.