Flowmaster has released three new performance exhaust kits for the 2024 to 2025 GM 1500 pickups with 6.2-liter V8 engines. They are the first aftermarket exhaust kits for the newest Chevrolet Silverados and GMC Sierras that seamlessly replicate the factory active-valve functionality.

GM’s active-valve exhaust system became optional on factory 6.2-liter trucks for the 2024 model year. Because buyers reacted enthusiastically to its introduction, the active valve is now standard equipment.

Flowmaster’s new active-valve exhaust kits work just like the factory systems: the driver can switch the exhaust note from mild to wild depending on the drive mode, rather than requiring an additional remote fob. Unlike with the stock mufflers, however, the louder mode in the Flowmaster setup is achieved by opening a dump pipe exit, before the exhaust gases reach the muffler, rather than opening a bypass in the muffler itself.

The three new active-valve kit options are as follows:

“When the customer puts the standard truck in sport or off-road mode, it gets a little louder,” explains Mark Emerson, Holley’s exhaust business leader. “These new kits retain that Jekyll-and-Hyde experience but are a two-in-one upgrade: you get a better, more aggressive performance tone in general running, but the exhaust note also gets a lot louder when you switch the truck into sport or off-road mode.”

Currently, most of Flowmaster’s aftermarket competitors do not retain the active-valve functionality in their performance exhaust systems. Instead, they use a valve simulator so that the customer does not get a check engine light when they swap the exhaust.

Flowmaster’s new kits are manufactured and welded in Bowling Green, Kentucky. They were developed from the existing cat-back systems for the 2019 to 2023, 6.2-liter GM 1500s, which have very similar engines and platforms to the current models. Engineers then tapped into their experience of active-valve systems previously developed for the Camaro, Mustang, and other vehicles, to add an active-valve assembly to the truck setup. Finally, they hit the road to thoroughly test the new kits.

“We already had the muffler designs for this engine, so the focus was on incorporating the active valve into the system and making sure we could retain the factory control and mechanism,” adds Emerson. “In our setup, the customer simply takes the factory actuator off the stock exhaust system and then bolts it onto the replacement. Everything works like stock from the dash. Mechanically, the truck doesn’t know there’s a difference. There are no changes needed to the powertrain control module and there is no impact on the factory warranty. But you’ll know the exhaust has been changed because of the sound.”

Shop Flowmaster American Thunder GM Active-Valve Systems here.

Shop Flowmaster Signature Series GM Active-Valve Systems here.

Shop Flowmaster Flow FX GM Active-Valve Systems here.

The three new systems are all cat-back replacements for the stock exhaust with a switchable dump pipe ahead of the muffler. All three come with a limited lifetime warranty, too. But they have different muffler designs to offer different sound characteristics, and are made from different materials, in line with their market positioning.

All three setups are designed specifically for the 6.2-liter GM trucks. But where the American Thunder system (above, left) uses a chambered muffler for a more aggressive exhaust tone, the Signature Series (above, middle) and the FlowFX (above, right) both use a packed, straight-through sound muffler.

Another difference lies in the tailpipe tips: the Signature Series and Flow FX both retain the factory bezels in the bumper, but for the American Thunder (below, right), you remove the bezels and use larger, dual-exit, black tips.

Finally, there is a difference in materials between the Signature Series and the other two kits: while the American Thunder and Flow FX systems are made from 409-grade stainless steel, the Signature Series kit – like every other kit in that line – is made from 304-grade stainless steel, for even better corrosion resistance. A brushed-metal finish and TIG welding add to the premium look of the Signature Series kit.

Despite the differences in construction and exhaust tone, all three kits offer the same performance benefit to 6.2-liter GM truck drivers. Flowmaster’s dyno testing shows that the upgrades bring a 15-horsepower increase

over stock as well as 13 lb-ft more torque. Emerson says those gains come mostly from the more free-flowing muffler designs, but also from the cleaner routing after the muffler. The factory routing goes from dual to single, and back to dual after the muffler (American Thunder System pictured below).

“The extra torque helps with towing, but we know that for many customers, the attraction is a performance exhaust tone that gives the truck a little more personality,” he adds. “Truck owners love to customize their rides and attract a little more attention. When you flip the switch on the dash you can really wake it up. But if you need to be quiet in the morning when you’re leaving for work, you can keep it on the milder setting and open it up when you want to.”

Installing the new exhaust kits is a straightforward process. Customers who want to perform the install themselves should be able to do so at home with basic hand tools, according to Emerson.

“It’s much like installing any one of our other cat-back systems – just plug and play,” he says. “I’ve installed many similar systems on driveways. Aside from the pipes, the only thing you need to add is a small harness extension for the valve, which is provided with the kit. There’s no rewiring required – just unplug the factory electrical connection and plug it back into the extension.

“We think truck owners will be excited by these new systems, which offer a great exhaust note and a handy performance benefit,” he concludes. “They are also priced competitively against the rival products, most of which do not retain the active-valve functionality.”

Shop Flowmaster American Thunder GM Active-Valve Systems here.

Shop Flowmaster Signature Series GM Active-Valve Systems here.

Shop Flowmaster Flow FX GM Active-Valve Systems here.