Description
Overview
The Flowmaster American Thunder Crossmember-Back Exhaust System is engineered to give classic muscle cars the deep, authoritative voice they’ve always deserved. Purpose-built for 1967-1974 Camaro and Firebird models, as well as 1968-1974 Nova, this complete dual exhaust upgrade replaces the restrictive factory setup with mandrel-bent piping and a genuine Flowmaster performance muffler for a noticeable step up in both sound and flow.
At the heart of the system is Flowmaster’s exclusive 80 Series Crossflow muffler (part #42585), a moderate-tone performer that tucks up high behind the rear differential for a clean, tucked-away look and improved clearance. Dual 2.50-inch mandrel-bent head pipes feed the system, complete with a built-in H-pipe crossover that balances exhaust pulses for a richer note and stronger performance. Dual 2.50-inch tailpipes finish the job, delivering the signature American Thunder sound both inside and outside the car.
Key Benefits
This aluminized steel system is designed as a true bolt-on for enthusiasts restoring or upgrading their classic. Everything comes together with U-bolt clamping and includes all parts, hardware, and illustrated instructions to make installation straightforward. Because it’s a crossmember-back design, it addresses the exhaust from the crossmember rearward, giving you a cohesive, matched setup rather than piecing together mismatched components.
- Exclusive 80 Series Crossflow muffler for a moderate, deep, rich tone
- Dual 2.50-inch mandrel-bent head pipes with built-in H-pipe crossover
- Dual 2.50-inch tailpipes for balanced flow and classic sound
- Aluminized steel construction in a silver pipe finish
- Muffler tucks up high behind the rear differential for improved clearance
- Complete kit with all hardware, U-bolt clamps, and illustrated instructions
- CARB (California) compliant, Emission Code 5
- Backed by Flowmaster’s 3-Year Limited Warranty
Options & Configuration
This system is set up for 2WD applications and ships without exhaust tips, which are sold separately so you can finish the look exactly the way you want. If you prefer stainless steel construction, Flowmaster offers optional system #817104, which is backed by a Lifetime Limited Warranty. A heat shield is not included with this system.
Fitment & Notes
Confirmed fitment covers 1967-1974 Camaro and Firebird and 1968-1974 Nova. Please note this system does not include manifold downpipes or header reducer cones. Convertible models will require adding 3/8-inch of shims to the stock factory X-brace for clearance, or purchasing the Hotchkis Performance Convertible brace (Part #1404). With its moderate tone, mandrel-bent piping, and proven Flowmaster muffler technology, the American Thunder system is a purpose-built upgrade for owners who want their classic to sound and perform as good as it looks.
