Everything Exhaust - Midwest Aftermarket
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Everything Exhaust

The lungs of your engine, if you’re looking to pump out more power from your diesel or gasoline internal combustion engine, there are three areas of Midwest Aftermarket that you should be considering:

  • Performance Tuners & Programmers
  • Air Intake Systems (a.k.a. Cold Air Intakes & Turbos)
  • And Exhausts.

This final category includes numerous options and can often be intimidating for newer aftermarket enthusiasts to get into. Indeed, it is easier to plug in a programmer and everyone likely understands how Cold Air Intakes and Turbochargers work, but Exhausts somehow seem complicated and elusive. But this doesn’t mean you shouldn’t consider an exhaust upgrade.

Many people ignore or wait to upgrade their exhausts until they’ve got everything else suped up. I fear that this important system is overlooked often because of how complex it seems and perhaps fears of breaking the law. We’ll explain all of this in detail both here and in our Product Center series, Exhaustive Series on Exhausts.

Laws Around Exhaust Systems

First, let’s quickly tackle the legal concerns because I figure this is one of the bigger reasons why people neglect their exhausts. Many individuals think of so called “illegal” upgrades (or another way to put this would be “not street legal”), which include CAT Deletes and DPF Deletes. These straight pipe inserts which cut the Catalytic Converter or Diesel Particulate Filter out of your exhaust system technically remove your ability to legally drive your vehicle on the street for the most part. These products are still legal to sell for racing and off-road purposes and few limited industrial / commercial applications.

In other words, if you’re buying a CAT or DPF Delete, you are probably doing so for racing purposes. Now we would never tell you how to supe up your ride, but the Catalytic Converter and DPF both filter harmful chemicals out of your exhaust and keep them from mixing with the air. Seeing as we all need air to breathe, it is kinda important.

Back in the day before CAT’s were invented, air pollution from automobiles was a really big deal. People living in the big cities around the US would often be hit with toxic fumes from Interstate highways on the daily. This lead to the formation of the EPA and mandatory inclusion of Catalytic converters on all vehicles, and later DPF’s too. So if your vehicle has to pass EPA Emissions Tests on the reg, like mine do, then you should probably keep your CAT and/or DPF intact.

Now none of this means we’re judging anyone for considering or purchasing a DPF or CAT Delete. Each their own. It’s your vehicle, after all. And if you’re racing, off-road or on the track, yeah, you’d be silly not to consider this aspect of your exhaust as ripe for upgrade. Which leads me into the main point of why individuals should consider updating their exhausts in the first place.

The Importance of Air Flow

I always harken back to shop class, all those years ago. My mechanically inclined teacher posed us with a question that we should have known only appeared to be really easy. He asked, “What fuel source does your standard internal combustion engine run on?”

The answer was so obvious to us, that we obviously should have hesitated and double checked before blurting out: gas! Of course, we meant gasoline, or diesel, petrol if you’re British. Yo, Brits! What up? We weren’t completely wrong. But Teach just shook his head. He was looking for an answer that did indeed involve something gaseous--air. Or more specifically, Oxygen.

Now again we were only “wrong” on a technicality. I mean, obviously an ICE (Internal Combustion Engine) won’t run without petroleum fuel. But what our shop teacher was trying to emphasize was the importance of the air, specifically the Oxygen component of the air, in that cycle. He had us on a technicality though because the fuel (gas or diesel) is really more of a catalyst. What really makes the explosion occur is the Oxygen in the air.

If you had a vacuum, completely devoid of any air, we could demonstrate this function quite easily. Unfortunately, not too simple to come up with a vacuum filled with gas. But if you had one, and you tried to light it on fire, to ignite it (don’t try this one at home, kiddos), first you couldn’t get get a spark. In order to have fire, after all, you have to have air. And what’s the important element (molecule, really, but who’s counting)? O2, biotches!

The Bourne Propane Explosion

Here’s a great example: every seen the iconic film Bourne Identity, the first in the epic series following that crazy but lovable spy, Matt Damon--er… Jason Bourne, I mean. Anyway, there’s a scene near the end of the film when Borne is trying to get a propane tank to explode. First time I saw it with a date, and afterwards I was all hyped up and excited about it. I mean, it’s a pretty cool flick--a guy movie, perhaps, but some nice spy noir stuff.

So this gal says to me after the movie that the propane scene was silly or at least confusing. I’ll give her the benefit of the doubt. I wouldn’t have understood it either without shop class and my father teaching me everything I know about cars and such. My date explained that she thought it was odd that Jason Bourne had to shot the propane tank twice to get it to explode. She found this very confusing. And I can understand. I mean, we are trained from watching various action flicks that the second you pump a few rounds into any car or truck, the whole thing will explode in a fireball of epic death. Of course, in real life there are things called physics. But in movies, stuff just magically explodes.

So she thought it was really odd that the propane tank in the film doesn’t explode after the first shot. And I had to explain to her that the propane is really just a catalyst. Inside that compressed tank of fuel, there’s no oxygen or air of any kind. The tank is sealed. And as I said before about sparks, you can’t get any without oxygen present in the air around you. There be no oxygen inside the tank, hence no spark, so no ignition.

But once Bourne puts a hole in the tank, air starts rushing in and propane starts pushing out. Whether it is the oxygen no presumed to be squeezing into the tank filling the pressure void or the propane outside mixing with the air that ignites on the second shot, beats me. But I can tell you this either way, that explosion only happens because of the oxygen. Without it, you don’t get no boom! That or I suppose they may have used fancy movie magic and CGI. What do I know?

Back to Shop Class

So our shop teacher had us… on a technicality. And it turns out he had done so deliberately. Sneaky teachers! Because the unit we were moving into was all about Exhaust Systems. And Exhaust Systems and Intake Systems, working hand in hand, keep your cylinders (whether you have a humble four banger or an epic 30 cylinder Sherman tank--look it up! You can’t make this sh!t up!) firing. Or as the shop teacher might have put it, “If you ain’t got no airflow, you ain’t got no get up and go.” Man, I miss that class.

So the point of these anecdotes is to emphasize the importance of airflow to your engine. And while a lot of customers focus on Turbochargers and Air Intakes, which is a great place to focus on, don’t get me wrong, we often neglect the other end: the Exhaust. 

Alright, so Exhaust systems are important. And it has something to do with air flow. We get it, right? Wrong! You haven’t heard the half of it just yet. Cause at this point you might think that Turbo’s and Air Intake are the most important cause they pump the air into your cylinders. And you’d be partially right. But the Exhaust is also important because of two very important terms I’m about to edu-ma-cate you about: backpressure and scavenging.

What is Backpressure?

What does exhaust backpressure mean?

Backpressure is the amount of air pressure holding back or restricting the flow of an exhaust system. Backpressure is caused by any restricting elements in your exhaust which might slow down the flow of exhaust gases through the system and out the back of your vehicle.

Why is this a big deal? Any restriction or backpressure means that your engine will have to work hard to push new air and fuel mixtures into your cylinders and pull exhaust fumes out. That process (related to scavenging, see below) if done poorly, costs you power or work. In other words, your engine doesn’t function at top efficiency and some of the power (work) that should be used to make your tires spin has to be used to pull in the air and push out the fumes. This makes your engine perform below optimal levels. And we simply cannot abide that!

What are the main causes of backpressure in an Exhaust system?

What causes backpressure?

Any airflow restriction in an exhaust will cause backpressure, but specifically the main causes are:

  • Exhaust Pipes that are Too Small
  • CAT & / or DPF Restriction
  • Inefficient Stock Mufflers

As stated before, we really can’t do much about the CAT or DPF issue, at least not legally. But you can certainly replace your stock CAT or filter with an aftermarket one to improve your air flow. Beyond that, you’re either rocking an illegal ride or stuck with some kind of CAT / DPF restriction.

So we’ll focus on the other two.

Optimal Exhaust Pipe Diameter

So here’s the thing. Many of us, especially aftermarket people, not unlike myself, often jump to the conclusion that when it comes to exhaust pipes, bigger is always better. While that isn’t totally wrong, we do need to slow down a bit. First, it really isn’t necessary. In fact, putting a 5 or 6 inch exhaust pipe on anything street legal is probably a waste of money, time, and space beneath your vehicle.

But why, you might ask. Didn’t you just say that pipe restriction is a big deal, that backpressure is bad for your engine?

Yes. Yes, I did. But slow down partner, cause that’s only half the story. You do want to cut down on backpressure, but you also don’t want to over do it either. It would be silly and actually incorrect to say that a 5 inch pipe is what’s best for every vehicle. Not only is that much airflow unnecessary for your engine, but it actually--drum roll please--is bad for your engine, at least when it come to optimization. And here’s where we come upon that other term I promised to explain: scavenging.

What does scavenging do for your engine and exhaust?

What is engine scavenging?

Engine scavenging is when your exhaust fumes accelerate at the optimal velocity such that a miniature vacuum is created, pulling exhaust fumes from the next cylinders as they open, aiding in sucking fresh air in. This process increases horsepower and improves overall performance of your engine. But in order to achieve it, you need to be in that optimal zone a.k.a. the hot zone.

So we want to lessen the restriction of airflow, yes. But we also don’t want there to be so much room in that exhaust pipe that the fumes don’t fill it. Because we need a tight vacuum to form if we want our engine exhaust to properly scavenge. This means that each and every stroke of the engine after the first aids the next and so on.

The optimal size of your exhaust pipes does vary depending on how much displacement and horsepower (HP) your engine has. There’s a lot of math that goes into this, and while I have links to several great sources in our article over in the Product Center, I’ll just leave this handy little chart here to help you.

If you have a dual exhaust, then you actually want roughly half the diameter because--duh--now you have twice the exhaust pipe, double the volume of fumes that can pass through it. Check the chart and use the 2017 stock examples or if you know roughly how much Horsepower you engine puts out, use that to find the right pipe size for your vehicle.

Optimized Exhaust Diameter Chart

So what does this all amount to really if you want to optimize engine performance? The best way to do so is to ensure you have the proper pipe size all the way down, starting with your headers on down to that Muffler Tip. And the best way to do that is to pick up a full Header Back Aftermarket Exhaust System. They are the most expensive, but they are also the most efficient. So if you’ve got to have the best, this is really the only way to go.

Don’t want to mess with an aftermarket CAT or DPF? Then try a CAT-Back or DPF / Filter-Back System.

Just looking for sound? See below.

Now that we’ve got that pipe diameter stuff and exhaust terminology out of the way, let’s talk about what we really want to talk about: Mufflers!

Mufflers & That Rumble

I get it. I’m all about that science and gearhead knowledge. But I understand that most of us really just want a sick sound. No worries. You need either an Axle Back Exhaust system or just a new Muffler.

When it comes to mufflers, the sound is really personal. The most aggressive sounds come from “Straight Through” Mufflers, which look more like slightly thicker sections of downpipe. Often referred to as “glasspacks,” you know ‘em when you hear them.

If you want more of a nuanced purr, a split tailpipe muffler can be a great option. These are those mufflers that have two tip pipes coming out of them. While they aren’t true dual exhausts, people often think of them as such. And in my opinion, they have a nice sound to them, even though they aren’t the creme-de-la-creme or as popular as glasspacks.

True Dual Exhaust Mufflers are where it is at for true exhaust aficionados. If you want an optimal exhaust system, you’ll need the right pipe diameter all the way back from headers on down, a Turbo, true dual exhaust, an X-pipe, and dual mufflers to boot. Not only do dual exhausts sound great, but they also offer a range of decibels, including the maximum street legal sound from the Borla ATAK dual mufflers. Baby, that’s aggressive sound!

Again, muffler rumble really comes down to the individual ear. So don’t let me tell you what you like. You make sure muffler wise you get what you want. As far as backpressure goes, any aftermarket muffler is pretty much guaranteed to be better than your stock muffler. While many swear by “straight through” mufflers as the least restrictive, remember that you need some scavenging too. In other words, the other muffler types should not be ignored by your true exhaust experts either. So don’t leave this guide thinking glasspacks are the only way to go. I actually like dual exhausts with more standard mufflers myself than straight throughs.

The Numbers

Believe it or not, we’ve really just scraped the surface of all the important aspects of aftermarket exhaust systems. If you want a more exhaustive explanation, see the article series in our Product Center that I’ve been mentioning throughout this quick guide.

But if you just want quick numbers on how many horses you can add to your engine by upgrading piecemeal, I’ll tack those on here. Keep in mind that these are rough estimates only, and each provides a pretty huge range of possible gain. So your mileage may vary.

How much Horsepower does any one aftermarket exhaust or performance part add to your engine?

How much HP gain can I expect on average for any single aftermarket performance or exhaust part?

If you were to have a stock engine and upgrade just the listed part, this is an average range of what kinds of horsepower gains you should expect to see:

  • Just Headers: 20-30 HP
  • Header-Back: 15-20 HP
  • Cat-Back: 5-10 HP
  • Aftermarket Cat: 10-20 HP
  • Performance Tuner: 10-50 HP
  • Large Diameter Throttle Body: 25 HP
  • Turbo Charger: 25-60% Gain (or 1.25 to 1.6 times your stock HP rating)

Math done. I hope this quick guide to exhaust systems helps you understand both the importance of your exhaust system and where you might start your upgrade journey.

When you’re ready to pickup that Header-Back Exhaust System or just a Muffler and some new Tips, we hope you’ll do your shopping here at Midwest Aftermarket.

Our collection of exhaust systems, mufflers, exhaust pipes, and much more includes all the leading styles and brands. Midwest Aftermarket is the #1 online retailer for aftermarket truck and Jeep accessories, selling products at the lowest prices and providing the best customer service in the industry. With the goal to provide the highest quality product with the fastest shipping at affordable prices, look no further for your vehicle’s aftermarket accessories. From UTV’s to Jeep-fanatics to F150’s or Chevy Silverado’s, Midwest Aftermarket will give you the customer support you deserve.