new to forum, need help

Hello, I'm totally new to this forum and don't know where else to post to find help. I just bouggt my first truck, an 04 hemi 5.7L 4x4. I need to get a muffler put on it for safety. It is currently true duel and straight piped. I'm young and don't have a lot of money, so I just want a muffler as cheap as possible without loosing any power. I was considering buying a magnaflow duel in/duel out muffler and putting two tailpipes side by side straight out the back, or joining the two pipes into a 4" or 5" output, probably from a diesel exhaust from the auto wreckers with a muffler. Dont want to buy two seperate mufflers for each pipe because i would have to put in too many joints in one pipe which would be more costly than the magnaflow. Not an expert on trucks either. Located in Canada, what do you recommend? Thanks!

your on the right track..I would just do the duel in/duel out magnaflow so that it would be minimal work for installer...

I did some pricing today and it seems that it would be a cheaper route to pipe the duels into a single but bigger pipe such as 4 or 5 inches in diamiter and putting a cheap thrush glasspack on, instead of the magnaflow and two pipes of smaller diamiter. Would this effect power and sound in any major negative way vs the magnaflow with two exit pipes?

yes...unless you've dome major mods, I wouldn't go bigger than a single 3" pipe on the exhaust side...you will lose so much low end torque..

I did the duel to single set up...my motor is stroked but I made sure the rear was no bigger than 3.5"..

Mostly stock truck don't go bigger than 3in, it's not a diesel. A gas engine needs smaller pipe to keep the velocity up. If you go to big your exhaust will have more room to flow but it won't have the velocity to help scavenging. Think water hose open it full bore you have a lot of water coming out now cover half the end, the same amount of water comes out faster. That will help scavenging witch will increase your tq. On a stock hemi or close to, you need single 3in or dual 2.25.

Edit: if you are trying to keep cost down check mbrp or jones full boar muffler they are both perforated stright through designs (like Magnaflow) but a lot cheeper you can get a 409ss for the $60-$70 range. Just check case length the shorter the louder common are 14,18,20,24 the 14 will be loud the 18 moderate and the 20-24 and not much louder than stock at all.

Thanks everyone your input has helped a ton. So on a gasoline engine, some amount of back pressure will increase torque? So if I did the idea of joining the two duel mufflers into one pipe, it would be wise to run anything between 2.25 to 3 inches in diamiter for output? And this increase of back pressure and torque won't have any negative effect on overall horsepower or fuel economy? Because fuel efficiency is also key.

I just read a few awesome articles on exhaust velocity, scavenging, back pressure, etc. And now I understand the concept. It seems the trick is finding the perfect restriction and exhaust diamiter to produce the proper velocity at a desired rpm for the peak of the power band. With the dual pipes joined, how could I figure out the perfect diamiter of pipe with a simple glass pack muffler for best efficiency at around highway cruizing rpm, but still have lots of torque to achieve good acceleration? So much more complicated than I imagined.

Yeah there is a lot that goes into it but basically you want the smallest pipe that doesn't cause back pressure. Back preasure is a miss used term in the exhaust world. "Back pressure" is actually pressure going back into the engine witch would cause all kinds of issues. I will be the first to admit I use to call it back pressure till I was corrected one day and did all kinds of research on it. But to simplify things on a stock hemi you want dual 2.25 or single 3in and a stright through muffler, the perforated core mufflers are stright through but will quite down the exhaust quite a bit. Glass pack will be super loud.

I'm aiming for a loud exhaust, and the one glass pack I'm looking at is a long one, somewhere around the 20" range and says it's a straight through design so that with a single 3" at the end should be perfect. I just hope switching from dual to single won't have any negative effect on power or fuel efficiency outside of the powerband

Hi Thebear,

You will find more low end torque and power down low where it is usable in normal driving. Duel exhaust, true duels, allow for more gas flow at higher rpm. They are great for drag cars, race vehicles because at max rpm they flow good exhaust. The principle being that two pipes can move more air because they offer a larger flow path. But the caveat is that you pay for that flow in low rpm torque and power. The 3" single will give you good low end power and torque and might improve your gas mileage because you have power where you use it most of the time. As for the glass pack what ever floats your boat. The idea behind any kind of tuning, be it intake gas charge, timing, exhaust is to make the most power where you will use it most of the time.
have fun and Merry Christmas

preachp

preachp said:

Hi Thebear,

You will find more low end torque and power down low where it is usable in normal driving. Duel exhaust, true duels, allow for more gas flow at higher rpm. They are great for drag cars, race vehicles because at max rpm they flow good exhaust. The principle being that two pipes can move more air because they offer a larger flow path. But the caveat is that you pay for that flow in low rpm torque and power. The 3" single will give you good low end power and torque and might improve your gas mileage because you have power where you use it most of the time. As for the glass pack what ever floats your boat. The idea behind any kind of tuning, be it intake gas charge, timing, exhaust is to make the most power where you will use it most of the time.
have fun and Merry Christmas

preachp

Click to expand...

Yeah single 3in on a stock hemi is perfect and that is what comes on the trucks and engineers put alot of time into exhaust design to make sure the have the proper exhaust system. The reason there is room for improvement is they have 2 goals in mind when building a system cost and being quiet. There are couple restrictive parts in the hemi's factory system and that is the y pipe and the muffler. The y pipe is crushed pipe and it just doesn't flow very well.( that's the cost part it's cheep To build them This way) The muffler is restrictive by design as it needs to be quiet. So imo the best you can do for exhaust is replace the factory y pipe with a Magnaflow and replace the muffler with a stright through design and leave the rest of the factory pipe it's ss so no need to change it.

Thanks for your help everyone