Breathe Out: Flowmaster’s American Thunder Exhaust On A 2015 Tacoma

FLOWMASTERTACOMALEADART_2It’s an unfortunate fact of life that you can’t teach yoga to a truck. What are we talking about? We’re talking about the fact that a truck can only breathe one way from the factory. A truck’s “lungs” cannot be controlled by meditation or concentration, but there are other ways. ECU mapping, porting and polishing, intakes, exhaust, and other modifications open up a wealth of possibilities to take a giant metal air pump – the engine – to get it working harder, faster, and better.

IMG_7478When presented with this 2015 Toyota Tacoma, we saw a truck that had the basics nailed down. After all, it had the TRD Off Road package, which slapped on off-pavement goodies like Bilstein shocks and an electronically controlled locking rear differential. Dual-range four-wheel-drive and a set of BF Goodrich Rugged Trail T/A tires rounded the capabilities of this midsize. The owner was proud of his pickup, but found the pick-me-up to be a bit lacking and was game to try an exhaust upgrade and see what came of it.

We knew just the folks to see about this situation – Flowmaster. For over 30 years, the company has made great strides in the exhaust market as cars, whether meant for street or competitive use, have been fitted with Flowmaster’s kits. That’s saying nothing of the company’s efforts with trucks, which have been in production since the early 1990s. After all, racers need tow vehicles well-equipped to haul vehicles around to various events, which was how Flowmaster got invested in the truck market in the first place.

Where this concerns our Tacoma is the American Thunder cat-back exhaust system (PN 817614), a mid-level upgrade that we hope will produce not just additional horsepower and torque, but also an exhaust note that puts a grin on the owner’s face every time he goes for a joy ride. Before we got to the installation, we talked with Flowmaster’s Dale Dotson for a complete understanding of the company, the product, and the customers that pave the way for improvement.

Discussion With Dale Dotson


Part of what makes Flowmaster so appealing to upgrade-hungry customers is its catalog. Over 350 kits are available, split up across four distinct product lines that serve various markets. These lines include Outlaw, dBX, Force II, and American Thunder. The first two address mostly car applications in terms of racers and imports, while the last two concern those of us who love our trucks and Jeeps. As Dotson explained, exhaust systems are not a one-size-fits-all affair; most truck and Jeep applications have at least two to three choices to offer customers the sound level they think is right for them.

IMG_7530“Our Outlaw kits are all about sound,” said Dotson. “They use either our Outlaw or Super 10 series muffler. Whether inside or outside of the vehicle, you will feel how loud and aggressive the exhaust is once it’s installed. The dBX kits utilize our dBX series muffler and offer a deep, moderate tone inside and out. They’re usually for smaller-displacement motors like those found in imports.”

“Force II kits are for our customers that want a more mild tone in their exhaust systems while still maintaining the same power improvements as our series,” continued Dotson. “They often use a three-chambered style muffler like the Super 50 series, or a combination of a two-chamber and a resonator to help with additional sound control. Finally, the American Thunder series constitutes our most popular offering. It uses our two-chamber design like the Super 44 series, and it’s aggressive outside and noticeable inside.”

Having started research and development in the early 1990s, Flowmaster’s efforts in the truck market have come a long way. Dotson commented that coming in 2016, the company will release side exit “muscle truck” systems, but could not offer any additional details regarding makes or models. Custom-made kits are no longer offered, but a compromise can be reached by using Flowmaster’s U-Fit dual pipe kits to design a unique, mandrel-bent exhaust system specific to any application. “This allows users to choose the muffler that is right for them and their application,” he said.

IMG_7524For the purposes of this truck and its owner, the American Thunder kit should prove to be just what the doctor ordered. Coming from the factory, Toyota fits these trucks with a single-inlet, single-outlet exhaust system measuring 2.25 inches in diameter. This new aftermarket kit widens it to 2.5 inches, offering a more optimized and opened-up flow path for exhaust to escape.

As far as the muffler is concerned, it’s the Delta Flow factor that adds a dimension of performance to the overall kit. “Our Delta Flow technology comes from our race mufflers,” said Dotson. “We found that by adding additional smaller deflectors behind the initial deflector, it would help to maximize the scavenging effect and help to cancel some unnecessary sound both inside and outside the vehicle.”

IMG_7518Add that to its stainless steel and mandrel-bent construction, and it’s a powerful combination for this midsize pickup. Then there’s the matter of adding an additional exit to the overall system, making the truck look far more aggressive and stylish when the install is complete. Dotson noted, “There is no real performance improvement when going to a dual exit kit. The additional tailpipe is more of a cosmetic thing. Because of emissions regulations, we cannot change to a true dual system on vehicles that came with a single exhaust. The main performance benefits in these types of kits comes from the muffler design.”

As a clean-cut, bolt-on system, our American Thunder kit should prove a worthwhile modification. Let’s get into how we made it happen on this particular Tacoma.



If you’ve ever done a cat-back installation before, this is not all that different in terms of ease despite having dual exits. The Flowmaster kit was actually well-designed to make its way around the axle, suspension, spare tire, and other parts of the undercarriage without issue.


Once it’s unattached from the vehicle, the stock exhaust system comes out and over the axle for complete removal.

The work began with the exhaust flange just behind the transfer case, where two bolts were removed. Rubber hangers suspending the exhaust tubing were taken down front to back, and the entire length of the exhaust system was removed in one fell swoop.

A comparison of the stock versus Flowmaster exhaust systems.

We laid the old system down next to our Flowmaster system to get a tit-for-tat comparison. We noticed a striking difference in the way that the over-axle tailpipe was shaped, as Flowmaster’s design stepped up and then down for a smooth flow rate, where Toyota’s stock system was a quick “V” shape that was hardly optimal.

A hanger was placed on the driver’s side of the truck, just aft of the leaf spring’s rear mount. This would be where the opposing tailpipe would mount once we were ready for that section of the install. We found that having the spare tire in the way just wasn’t helpful at all, so we removed it at once.

The tailpipes are attached to their hangers to wrap up the install.

We grabbed the new Flowmaster center section and bolted it to the flange, with the shock-absorbing springs once again surrounding the bolts as they did for the stock setup. The muffler was attached to the length of pipe, and the tailpipes were fitted to the muffler’s outlets. Once the hangers were reattached to the rubber grommets, we secured the slip-in joints with U-bolts (the kit comes with hose clamps, but these proved too weak as the bolt heads sheared off while tightening). And with that, our installation had wrapped up. Now it was off to the Dynojet dynamometer to see our results.

Dyno Testing


We did two runs prior to our Flowmaster install to see just how much horsepower and torque the Tacoma was making from its factory setup. Once it was safely strapped down, we hopped into the driver’s seat and got the rear wheels rolling.

The results showed us the truck (running on 87 octane) was making 188.0 horsepower and 225.4 pound-feet of torque, which was right around what we expected when factoring in a driveline loss of 20-25 percent. Compared to our new readings after the installation, we saw an interesting difference.

Tacomabeforeafterdyno_1The horsepower had jumped up to 193.6 for a gain of 5.6, but our torque had dropped to 218.6 for a loss of 6.8. This was likely attributed to the fact that a wider-diameter system tends to lose torque, since raising the torque amount relies on constricting the diameter to increase exhaust velocity. The Tacoma was still running on a stock intake, so this was the best we were going to get in terms of numbers.

We took the Tacoma out and about for a test drive before and after the installation. Where sheer dyno numbers may have been bittersweet, the noise change definitely perked us up. Our video above will give you a taste of what the acoustic difference was, but suffice it to say it couldn’t do justice to actually tearing around the backroads of Murrieta.

Mashing the gas off of the stop sign was a lot more fun, for one thing. Hearing the 4.0-liter V6 shriek through second gear was all the more amplified with two exhaust outlets instead of just one. Before, we had to strain to listen to the exhaust at idle, but now it was a more guttural, grumbling tone that could be heard whenever we rolled up to a stop sign and waited our turn to go. Cruising was a mild affair with the stock system, too; here, it was pushing toward aggressive by letting the V6 vocalize.IMG_20151202_163713

To have all this – plus some none-too-shabby polished exhaust tips – worked to make this truck have an extra edge over its former self, both in terms of horsepower, sound, and looks. You can learn more about Flowmaster’s products on its website or by phone using the provided contact information below. And to stay up on all the latest and greatest in off-road content, keep it locked here on Off Road Xtreme.

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About the author

David Chick

David Chick comes to us ready for adventure. With passions that span clean and fast Corvettes all the way to down and dirty off-road vehicles (just ask him about his dream Jurassic Park Explorer), David's eclectic tastes lend well to his multiple automotive writing passions.
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