This Instructable is for the DIY tinkerer with a fixation on HORSEPOWER!

Firstly, you should know why we want to change the exhaust to a high performance setup.. Every vehicle of any make/model that rolls off of the production line has an ill equipped air intake and exhaust system. Restrictions are put in place on both of those systems to limit the amount of noise a consumer will hear. I suppose auto manufacturers have to appeal to a very broad audience as far as buyers, so they make the vehicle as quiet as can be.. The problems with that is: IT REDUCES YOUR VEHICLES POWER AND GAS MILEAGE!

A simple understanding of VOLUMETRIC EFFICIENCY (VE) can help you understand why you can get better power and/or fuel economy by helping your engine breathe better. Volumetric efficiency is basically a ratio (or percentage) of what amount of fuel/air is being drawn into your engine as compared to the actual capacity that is possible. Think about breathing through a straw. Sure you can do it just fine while your sitting down on the couch vegging out, but if you decide to go jogging then its just not going to work out so great is it? 

When we eliminate the restrictions on the air intake system, we allow the engine to BREATHE much easier. We do this by putting a high flow performance air intake system on the vehicle. The amount of air that it will draw in naturally will be increased because there are no more intake resonators (restrictions used to quiet suction noise) or restriction stock paper air filters for the air to try to get through. By having more air entering easier than it used to you will not have to apply as much throttle to get up to speed. This is where your mileage can increase. Now when you want to have some fun and mash that pedal to the floor - you will have much more air available to create more power which is just plain fun. Gas mileage does not really increase when you drive like this though :(

Alright. Now, the engine can breathe in easier. Next order of business: HELP THE ENGINE EXHALE. The design of factory exhaust systems is horrible for the most part. All sorts of restrictions built in to keep that SUCK-PUSH-BANG-BLOW quiet. Mufflers are usually the most restrictive part of a stock exhaust system. The exhaust gasses basically have to maneuver its way through a series of walls, chambers, louvers, baffles, and other maze-like flippety-doo's.. This needs to be fixed! 

**A note on catalytic converters: Many people are under the mistaken impression that the converter is the 'bad-guy' that is restricting your power and want to remove it. DON'T! Converters on almost all late-model vehicles are designed with HIGH-FLOW catalyst biscuits. They offer just the right amount of back-pressure needed to maintain some bottom range torque, yet flow free enough to not hinder performance at the higher RPM range. Do your research and if you find that your converter is of a bad design then do the smart thing and upgrade - Not remove! I won't even get into EPA mandated laws and fines and violations etc...

There are lots of other factors that help with the power/mileage aspect of VE such as exhaust scavenging and valve overlap, but if you want to learn more you should do some surfing.

Step 1: Select the Right Performance Muffler. Do Some Research!


What we need now is a great muffler for our project. For the best performance I always choose Magnaflow mufflers because they are just plain awesome! They are stainless steel constructed inside and out and carry a lifetime warranty. They offer the same performance as straight-piping does, yet they have superior sound control and they are not going to get you pulled over..NO BACK-PRESSURE WHATSOEVER.  Another fantastic thing about them is that they do not sound like a "rice-burner" or a "bumble-bee in a coffee can". You know what I'm talking about.

When selecting a muffler for your project you need to probably take some measurements to find out what size to buy. You will also need to determine what "offset" you will need - meaning: Where does the muffler  inlet and outlet sit. Magnaflow mufflers are reversible so they are pretty easy, but note: NOT ALL MUFFLERS ARE REVERSIBLE.   About 80% of cars/truck have a side/center offset. The inlet is either in the center or the side and the same goes for the outlet... The mufflers I am using on this Challenger are "side-side" offsets meaning that the inlets/outlets are staggered opposites from each other.

Mufflers come in standard pipe sizes and are measure I.D. (inside diameter) while pipe sizes are measured O.D. (outside). A 2" muffler inlet is made to slip over a 2" pipe. The most common pipe/muffler sizes are: 1-1/2", 1-3/4", 2.00", 2-1/4", 2-1/2" and 3.00". Diesel trucks will usually have 3-1/2" to 4.00" stock sized pipe.

MUFFLER BODY SIZE: When it comes to Magnaflow mufflers and (most others too) the larger the body of the muffler the better sound control will be. There is usually a body length and body thickness measurement. Pick one that fits and also decide how loud (or not) you want your hotrod to be.

Step 2: Tools & Parts - Whatcha Need to Have (or Borrow)


* Hearing/Eyes Safety protection.
* Sawzall - Used for making quick work of muffler removal.  Use 14 tooth bi-metal blades
* MIG Welder - Unless you can clamp everything in place you will need one. Helmet too,
* Oxy/Acetylene torch - Used for heating exhaust hangers to 'wrap' them and for some cutting.


* Project car - I am using a 2010 Challenger R/T
* Properly selected muffler - See step 1
* Custom exhaust tips - If you are putting some on I'd recommend stainless not chrome.
* Hanger rod - Used for securing muffler where stock hangers were removed. Get some at an exhaust shop.

Step 3: DO-IT TO-IT! Commence the Chopping! Then Put It All Back Together.

Get the vehicle onto a safe four post lift or roll over pit. You do NOT want to hve the wheels/suspension hanging while you do this job.The exhaust will not sit exactly where it should if you try to do the exhaust while suspension is hanging.

Now the fun part. I just love cutting into brand new cars exhaust systems! Its fun. Make sure you check and double-check your cut before you make it. Hold the new muffler up under the stock one and get a good idea where its going to fit and where you should make your cuts. Use a new sawzall blade for the cleanest and straightest cuts. 

Once the exhaust is cut down its already time to start going back together. On this project I am doing 2 mufflers that have to fit the exact same on both sides. While I am fitting parts together I am going to put just a few very small tack welds on them. By doing this I can easily break the tacks if I need to reposition something. Check and check and check your positioning several times before the finish welds are made.

** You will want to view the job from ALL angles before finish welds as well. Just viewing from the bottom can give you a very messed up position when you actually look at it from above. I will often lower the car (or whatever I'm doing) in order to view it as I would when I am standing above it as I normally will.

At this point  I am still just tacked up. I had to make a couple minor tweaks, but I was very close on everything with the first tack welds. Make sure that you give the hanger rod a good strong tack before finish welds begin to ensure that the small tacks don't break and distort your positioning.

Step 4: Finish Up.

Ok. Everything is tacked and positioned perfect. My friend that owns this Challenger has decided to use the stock tips on this system for now. I will ALWAYS make sure to position and tack the tips on before the final welds are made on the muffler. You really don't want to have ruined the tip positioning on accident cuz its not fun. Do it in the right order and it is very hard to mess up.

* Mufflers are tacked
* Tips are tacked
* Exhaust hangers are wrapped. This is done by using te torch to heat the rod and then bending or    hammering the rod to match the curve of the muffler or pipe. It looks good when done like this and it also is MUCH stronger.
* Finish welds are done.
* Light coating of 'aluminum' colored high temp exhaust/block paint. This prevents ugly surface rust from  showing up and it looks nice. Only on welds/pipes though - Don't paint the mufflers. It will flake off.
*Tips are cleaned and polished - make sure to do this before firing up the engine. This will prevent any grease or fingerprints from getting burned into the nice shiny tips.

And the very best part = start it up -> rev it up ->rock it down the road to feel da power -> ENJOY!

Thanks for reading my first instructables!

Be the First to Share


    • Digital Fabrication Student Design Challenge

      Digital Fabrication Student Design Challenge
    • Colors of the Rainbow Contest

      Colors of the Rainbow Contest
    • Tinkercad to Fusion 360 Challenge

      Tinkercad to Fusion 360 Challenge


    Hmm, how come I cant cut and paste from above comments (I'm using Google Chrome)...Anyway, I am pretty sure, the claimed "improvements" only happen at high RPM's when you want maximum HP.  If the air filter/intake is rated for 150cubic feet per minute at 6000 RPM's, and at 1500 rpms when cruising you are only using 38 cfm....there will be no increase in HP or MPG at 1500 rpm.  I've looked at the "charts" for my ford focus 2l duratec, and the HP gains only happen way up there, down around, 1000 and 2000 rpms, the data is the same.  IF I am wrong, please let me know.  Bill.


    Reply 10 years ago on Introduction

    That is because there aren't any. At low RPM the HP boost is near undetectable. In some cases just replacing pieces and parts on your exchaust with performance parts without re-tuning the vehical is a bad idea.

    I have seen more than 100 late model dodge owner throw their low end torque in the trash just to gain 6 to 15 HP at the high end. Yes the new setup is less restrictive but without that restriction then you aren't generating torque.
    Now this is rarely an issue because most that would do these mods are looking for a meaner sound rather than over health of the car.


    11 years ago on Introduction

    Flowmaster super 44's are the way to go dude.


    11 years ago on Step 3

    woooow your car is really really cool man, I literally love that car x)

    Magnaflow mufflers are great because they give you the same PERFORMANCE as a straight-pipe exhaust because they are straight through. You can literally see through the muffler when you look in the inlet/outlet tubes. No restrictions whatsoever - BUT - You get GREAT TUNED EXHAUST SOUND. I've installed over a thousand Magnaflow mufflers and always have happy customers. Trust me - I am not paid to say that. Any straight through style muffler (Borla for example )will give you the same performance, but my preference is and will be Magnaflow just because of the experience I have had with them. Flowmaster is only good for making lotsa noise and gaining a slight bit more performance over stock. If you look inside of a Flowmaster (or flowmaster syle: MAC, High Output, Thrush, ect..) you will see why they are way restrictive compared to straight through style mufflers.


    Reply 12 years ago on Introduction

     im kinda a car noob. so magnaflows give you the same performance as open headers? 

    yo man
    yo man

    12 years ago on Introduction

    straight-pipe all the way! it's crazy cool! 

    They come with a 'manifold' rather than header. Most OEM catalytic converters these day are actually a "high-flow" style so you will not gain much if any by changing them.


    12 years ago on Introduction

    What about a high flow cat?

    Also, go these Challengers come with extractors or manifolds?