A question often asked is: Which muffler is better, Magnaflow or Flowmaster? Both exhaust brands have been around since the early 1980s, both have the word "flow" in their names, and both brands have a huge following within the ranks of enthusiasts. Their profiles are so similar that the casual observer may not even know that Magnaflow and Flowmaster are different. The confusion is understandable, the stakes are high, and the brand loyalties are deep on both sides, so why hasn't a responsible third party stepped up to declare a winner? After all, it's a question on the minds of enough people that it keeps coming up year after year without a real answer. The answer is: both.
From a technical standpoint, it's a pointless question to ask if Magnaflow or Flowmaster is better because most people don't know what they should really be asking. Does "best" mean the most pleasing sound or the most power? Is price also a factor? Are you comparing every muffler lineup or series in each brand, or only the style du jour on your favorite web forum or Facebook page? Both Magnaflow and Flowmaster have many muffler lines (16 for Magnaflow and 26 for Flowmaster) and this has made it mathematically impossible to declare one or the other superior even if that were feasible. Adding to the confusion, both companies have endeavored to make near-copies of each other's products (Rumble Exhaust is Magnaflow's de facto Flowmaster-style product and the FlowFX series is Flowmaster's Magnaflow-style product). And yet, you still want to know what's empirically impossible to know. We get it, and we want to drill deeper into the subject so that you can start asking the intelligent questions.
Dyno testing has revealed a lot of snake oil and mirrors over the years and we've discovered that on any given day, either a Magnaflow or a Flowmaster muffler (or another brand of muffler) can win. We aren't surprised that no brand has a statistical advantage on the dyno and that's because no muffler can add power—only take it away. There are, however, qualitative differences between Magnaflow and Flowmaster mufflers that we'll get into shortly, but first we're going to cover the other attributes of exhaust systems that are recognized by experts as being way more important.
Components of a high-performance exhaust system. (Image by David Vizard)
We hear this all the time, sometimes from supposedly smart people, and it's never true: "you need some backpressure to build torque in a street car." Backpressure never builds torque, an integral element of power. Backpressure only takes away flow and the more backpressure you have the more power it costs. The diabolical thing about backpressure that makes people think they're getting more low-end torque by their butt-o-meter is that backpressure robs torque more as rpm gets higher, leading people to think their low-end torque is magnificent when in fact their mid-range and top-end torque has evaporated. Hard as it is to believe, in the year 2021 you can still find thousands of YouTube videos, forum posts, and stories that state that you need to have a muffler with some backpressure to build torque. If backpressure really added torque, the names Flowmaster and Magnaflow would instead be Chokemaster and Magnachoke.
When folks start digging on the web for info about Magnaflow vs. Flowmaster mufflers, especially hard dyno numbers, they are ultimately looking for actionable information about making power through exhaust mods. Here, the thing that separates the women from the girls is headers versus stock exhaust manifolds. Headers, however, aren't always practical for a daily driver, but when they can be employed do offer the biggest power boost, used in conjunction with an upsized diameter system throughout. The header discussion is beyond the scope of this article, but h-pipes and x-pipes certainly are not, and once again these offer gains of a higher magnitude relative to fussing over which proprietary muffler design is best. Let's look at what's going on here.
Whether you choose a Flowmaster or Magnaflow muffler, either will benefit from some type of crossover pipe, and here's why. In a V-8 engine, the firing order from bank to bank does not always alternate, but repeats. This is to help compensate for crankshaft/bearing loads and balance concerns, and it means that cylinders on the same bank often fire consecutively. For example, in a small-block Chevy, cylinders five and seven are consecutive, as are four and eight. With all Ford V-8s, it's cylinders four and two, and seven and eight. Classic Mopars are eight and four, and five and seven. The Gen III Hemi fires four and two, and six and five consecutively, and even an LS (the engine with the least to gain from an exhaust crossover) fires cylinders two and six consecutively. At higher rpm, the behavior of these events acts as one longer pulse—a single slug of exhaust twice the normal size that can pile up and cause a restriction. Moreover, as the camshaft's overlap of the exhaust and intake lobe increases, the greater the positive effect exhaust scavenging—and a crossover pipe—has (see this Engine Masters dyno test of crossovers vs. straight pipes on a mild 5.3-liter LS with a 2.5-inch exhaust and a small cam).
The key to reducing backpressure from these consecutive bank firings is to merge the cylinder banks with a balance pipe—what we call an h-pipe or x-pipe. When an exhaust pulse encounters the crossover, the flow capacity of the alternate bank is shared, and a well-designed balance tube can act like an extra highway lane to relieve backpressure. Here, the type of crossover matters somewhat; a simple h-pipe crossover pays a smaller dividend due to the sharp right angles the exhaust must follow (the larger the crossover diameter, the better), while an x-pipe is better than an h-pipe at higher engine speed because it's like a traffic intersection where no turns are needed. So which muffler is best on an engine with serious power, Flowmaster or Magnaflow? Chances are, it's the one that's attached to a three-inch diameter dual system with an unfettered three-inch x-pipe.
After headers and some sort of balance pipe, the next most important thing—that's way more important than having a Flowmaster or a Magnaflow muffler—is keeping the heat inside the exhaust system. Doing this keeps the exhaust velocity high which in turn promotes good combustion chamber scavenging and power. Why? As the exhaust sheds heat the physical volume of the exhaust pulse—the slug from each firing event—decreases. (See Charles's law.) When the pulse's volume decreases from cooling, it's velocity and inertia also decreases, reducing the effect it has on cylinder scavenging—and power.
So while some dudes clack away at keyboards on message forums arguing about whether a Flowmaster or a Magnaflow muffler is best, you can spend that time pondering what kind of thermal barrier product you want to use on your headers, collectors, and x-pipe. These products can be wraps like those offered by DEI and Thermotec, or a ceramic thermal barrier coating from Jet-Hot or ZyCoat. Either way, power is headed in the up direction whether you've got a Flowmaster, a Magnaflow, or an ordinary $40 cheapo muffler. As a convenient byproduct, underhood temps and induction inlet temps will be less, further improving horsepower.
If power is way less of an issue between these types, why would it matter if you chose a Flowmaster or a Magnaflow muffler? It's all about the sound. Like a lot of people, I fell in love with the sound of Dynomax Super Turbo mufflers [Note: this is a personal preference, not an official position of HOT ROD], a class of muffler called a turbo muffler because its design was originally chosen by GM for turbocharged versions of the Corvair. Chevy bean counters liked the cost, engineers liked the minimal backpressure, and they didn't kill as much of the cool sound as the typical muffler of the day. Today, virtually every exhaust maker offers a version of the turbo muffler, including Magnaflow's BRExhaust line and Flowmaster's sister brand Raptor. They are generally inexpensive, have great flow when up-sized properly, and have a throaty burble that I like. As for the sound of Flowmaster's and Magnaflow's trademark muffler lines, I've used them over the years with success and can tell you these classic muffler designs work great and sound so different and distinctive that you can easily tell them apart blindfolded. We promise that when you hear 'em, you'll know which one you like best.
Flowmaster mufflers weren't the first line of high-performance mufflers out there, but they were the ones that aggressively went after the hot street car market, most famously in the 1990s with sponsorship of the HOT ROD Fastest Street Car Shootout, the precursor to today's HOT ROD Drag Week (fun Flowmaster trivia: Guy Fieri of The Food Network was a TV spokesperson for Flowmaster in 2008 and 2009 well before reaching foodie fame). Full-page ads featuring record-setting wheel-standing street cars wearing Flowmaster mufflers were a thing. The cars wearing Flowmaster mufflers were scienced-out in the exhaust department, with all the things we mentioned earlier, like properly-sized headers, thermal barrier coatings, thermal wraps, x-pipes, and short, sewer drain-sized pipes to dump the spent gases. Flowmaster mufflers rely on reflective baffles that create destructive interference at the most annoying drone frequencies—a tactic that cuts sound output, but that leaves significant sound energy in the "raspy" upper-midrange frequencies. And you would be correct to guess that the aesthetics of this are not always appreciated, even by some car guys.
While the Flowmaster muffler is essentially an empty box with metal baffles welded inside, the Magnaflow is packed with stainless steel wool. A perforated pipe of the same diameter as the inlet and outlet runs straight through the muffler case unimpeded, and the stainless steel wool surrounding the perforations soaks up the annoying frequencies like a sponge, turning the kinetic energy into heat, while passing the flow straight through the muffler. This design does a really good job of absorbing acoustic energy across a wide band of frequencies—especially midrange and upper-midrange frequencies. This type of acoustic dampening takes the edge off the sound while preserving the lower frequencies—the "rumble." From a flow perspective, Magnaflow mufflers are hard to beat (a straight pipe or a bullet muffler would be a good flow analog) and the Magnaflow sound is preferred by many.
Watch a Preview of ENGINE MASTERS Episode 49: $40 Muffler Shootout
We discovered from a comprehensive dyno test of 11 low-buck mufflers on MotorTrend's Engine Masters series (season 4, episode 49) that, categorically, mufflers with a straight-through design are measurably better power-wise than mufflers with any kind of baffle (the typical Flowmaster) or turbo-style mufflers similar to the Dynomax Super Turbo that I like. The comically simple litmus test for this kind of muffler is if you can see through the muffler from one end to the other. Where it gets tricky is Engine Masters only tested mufflers that at the time were under $40, leaving out the genuine trademark Flowmaster and Magnaflow products that everybody asks about. Engine Masters also kept x-pipes and h-pipes out of its test, a factor that would make a difference at the power level tested. Nevertheless, if we make the leap to accept empirically that all straight-through mufflers are better for power, then the Magnaflows would win over the Flowmasters had they been included. Instead, the low-dollar knock-offs of each were tested. How did they do, and what engine did they test with?
In Engine Masters episode 49, the guys used a 408 cu-in Ford Cleveland small-block dialed down to around 600 hp, and rpm was limited to 6,500; the important thing to remember is that the engine was chosen to lean hard on each muffler's ability to flow unfettered, magnifying any flow deficiencies in the muffler design. Each set of test mufflers had a three-inch inlet and outlet, an offset inlet, a centered exit, and an oval case with a length between 13 and 14 inches long. Long-tube headers were used and the baseline test was a three-inch straight pipe in place of a muffler. In short, relative to a straight pipe and no muffler, the Magnaflow-style mufflers (the ones you could see through from end to end) fared the best, the turbo mufflers fared the worst, and the chambered Flowmaster-style mufflers did only slightly better than turbo mufflers.
Cherry Bomb's Salute Magnaflow-copy muffler.
In an interesting twist, Engine Masters host David Freiburger deduced that the three 409 stainless steel Magnaflow-style straight-through mufflers under $40 were so similar that they must've been built at the same factory, so only the cheapest one, a Cherry Bomb Salute muffler, was tested (the others being a Jones Exhaust MAX Flow and a Flowmaster FlowFX) and it turned out to be nearly identical in power output to the straight pipe.
We still don't know whether Magnaflow or Flowmaster is best but based on the Engine Masters test series it looks like the Magnaflow would be the predicted winner between the two. Or is it? Like we said, both companies build knock-offs of each other's products, so the real winner between the two might be the stainless steel Flowmaster FlowFX, otherwise nearly identical to the Magnaflow, but at a price of $45.42 (each) instead of the Magnaflow's $115.
But what if, in a real Magnaflow vs. Flowmaster shootout, the Flowmaster were to turn out better than the Magnaflow? Then might Magnaflow's budget Rumble model (a Flowmaster replica, below) beat the original Flowmaster? These questions, however, are overshadowed by more important ones like do you have a two-inch diameter, 2.5-inch diameter, or three-inch diameter system? Are your headers coated or wrapped? Do you have an x-pipe or an h-pipe, or just straight pipes like in the Engine Masters test? Do you have a proper set of headers or stock exhaust manifolds? And most important of all, is your engine making enough power for any of this to make a difference on power?
In the end, the difference in power on a less powerful car may be so minimal that you may just want to choose mufflers with the sound you prefer. It's the choice this author made when selecting Dynomax Super Turbo mufflers for a 650hp 1968 Plymouth Valiant (below), a car whose traction woes far outstrip the need for more power. Like we said up front, the questions you ask are important; your car's power may benefit zero from a $115 muffler if the engine only makes 350 hp, and on the opposite end of the spectrum, you may already have too much power for the car's chassis, in which case you'd be better off spending the $115 (times two) on something else to get it to hook up, like a set of drag radials, a rear antisway bar, or some adjustable shocks.
For this author, the key to going faster lies not in which muffler to choose but in gaining more traction. Your issues may be in other areas still. On the other hand, if debating mufflers is your raison d'etre, then please carry on!