Frequently Asked Questions

Short answer: For a 350 convertible, the repro Long Branch manifolds (from Ram Air Restorations, ~$369, fit 1967–69, require the oil-filter adapter) flow as well as headers on a 350 without the header headaches. Factory “log” manifolds are cheaper and easier to find but lose some performance (though the 1969 Grand Prix 400 used log manifolds and was rated 350 hp).

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Short answer: Dual exhaust was standard on the 1967 H.O., 400, and Ram Air Firebirds, and optional on the others (including the 326 2-barrel).

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Short answer: Yes — the 350 and 400 D-port manifolds interchange (basically all 1965–70 Pontiac manifolds fit 1967–69 Firebird V8s; e.g., a 1973 350 pair fits a 1968 350). Only the Ram Air and H.O. “Long Branch” manifolds are hard to find (~$325/pair for ductile-iron repros, which are better than originals); all others run ~$100/pair. Beware used manifolds — 30 years of heat cycles leave many with stress cracks that are often worse than they look.

9779325 (RH)  63 T/4, 63-66 T/8-P/8, 67-68 F/8-T/8-P/8 (exc HO/RA)
9777755 (LH)  67-68 F/8
9791607 (RH)  67-69 F/8 Ram Air, H.O.; 68 P/8 428 H.O.
9779493 (RH)  67-69 F/8 Ram Air, H.O.; 68 P/8 428 H.O.
9779495 (LH)  67-69 F/8 Ram Air, H.O.; 68 P/8 428 H.O.
9777641 (RH)  67 GTO Ram Air, H.O.
9777646 (LH)  67 GTO Ram Air, H.O.
490802  (RH)  68 GTO Ram Air, H.O.
478141  (LH)  68 GTO Ram Air, H.O.
9796992 (RH)  69-72 F/8-T/8-P/8 exc HO/RA, 307
9796155 (LH)  69 F/8 exc HO/RA
9797073 (RH)  69 F/8-P/8 RA III, H.O.

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Short answer: On a convertible the limiter is the pan brace — getting anything bigger than 2.25″ past it (sharing space with the transmission tailshaft and driveshaft) is tough, though some have fit 2.5″ with creative bending/ovalizing. For ~400 hp from a 350, 2.5″ won’t be a plug.

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Short answer: The muffler-testing article you’re thinking of is Jim Hand’s “The Strong Silent Type” — extensive on-car testing of different brands (backpressure, sound level, 1/4-mile), plus tailpipe diameters and “H” vs “X” pipes.

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Short answer: Headrests were optional on 1967 (code AS2) and 1968 (code 571). For 1969 they became government-mandated — in two styles, straight (early, same as 1967–68) and curved (later).

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Short answer: The Long Branch cast-iron manifolds came on the 400 Ram Air and 400 H.O. engines (with the special oil-filter adapter) — not the 350 H.O.

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Short answer: Yes — the Long Branch (Ram Air III) manifolds bolt to a 350 block and are a big improvement over the stock “log” manifolds: better flow on any Pontiac V8, better ground clearance than headers, and a more reliable seal. The downsides are the oil-filter location (good solutions exist) and cost (~$400 new, plus ~$150–200 if you ceramic-coat them to preserve them).

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Short answer: Welding a cracked cast-iron manifold is a real science — it likes to crack again if done wrong. The method:

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Short answer: The 1969 Ram Air III “Long Branch” cast-iron manifolds are a smart choice over headers — better flow than log manifolds, a more reliable seal, better ground clearance than headers, and less noise and underhood heat (headers cook the starter/solenoid in a Firebird).

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Short answer: Members have installed the Flowmaster 2.5″ dual kit with crossover (from Summit and others) on a 1968 convertible. The 40-series mufflers fit, and the kit includes clamps and mounts that bolt to stock locations — but it comes with header flanges, so you’ll need a muffler shop to weld up the pipes from the exhaust manifolds (cheap reducers get you there). It sounds great: quiet at idle, aggressive when you get on it.

Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.