Porsche 911 991.1 GT3 GT3RS exhaust manifold

In 2026, finding an “as good as new” (low-mileage take-off) exhaust manifold for the Porsche 911 (991.1) GT3 or GT3 RS is a smart move for owners needing to replace a cracked factory unit or return a modified car to stock.

These manifolds are highly specialized as they incorporate the catalytic converters directly into the header design.

1. 991.1 GT3 vs. GT3 RS Compatibility

While the engines are both 3.8L and 4.0L variants of the MA1.75/76, the manifolds have a slight difference you should be aware of:

• GT3 (3.8L): Features high-flow headers with integrated cats.

• GT3 RS (4.0L): Physically identical in mounting flange, but often carries a different internal part number for the catalytic substrate to handle the increased flow of the 4.0L.

• The “R” and “Speedster” Factor: Manifolds from the 911 R or 991.2 Speedster are often sought after as “upgrades” because they are lighter, but they require the matching rear exhaust sections.

3. Identifying “As Good As New” Condition

When inspecting a used set, look for these “2026 standard” checks:

• Heat Discoloration: A “new” manifold will have a dull silver/grey finish. Once heat-cycled, they turn a golden-brown. If they are deep blue or purple, they have been driven hard or used on track.

• Internal Catalyst Grid: Use a borescope or a bright flashlight to inspect the honeycomb inside. It should be perfectly white/grey with no melting, crumbling, or “clogging.”

• Flange Flatness: Check that the 6-bolt engine flange is perfectly flat. Heat-warped manifolds will leak, no matter how much you tighten the bolts.

4. Critical Part Numbers

• Left Side: 991-113-021-72 (and revisions)

• Right Side: 991-113-022-72 (and revisions)

• Note: Always check the last two digits, as Porsche updates the catalytic converter density every few years.

5. Why Owners Sell These “New”

In 2026, most “as good as new” sets come from owners who immediately upgraded to Long Tube Headers (like Dundon Motorsports or Soul Performance) upon taking delivery of the car. These “take-offs” are the best quality you can find.