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.



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.
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.
dpr4 years ago
Flowmaster super 44's are the way to go dude.
tato3124 years ago
woooow your car is really really cool man, I literally love that car x)
InnovativeMotorcycle (author) 5 years ago
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.
 im kinda a car noob. so magnaflows give you the same performance as open headers? 
yo man5 years ago
straight-pipe all the way! it's crazy cool! 
InnovativeMotorcycle (author) 5 years ago
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.
Holden_vy_s5 years ago
What about a high flow cat?

Also, go these Challengers come with extractors or manifolds?