1970-1981 Trans Am: 400 Pontiac vs SD-455 Engine Specs (And What Was Actually In Your Bay)

Why this article exists

The second-generation Trans Am is the most engine-confusing American performance car of its era. Across its 1970-1981 run, "Trans Am" referred to a body and trim package that was fitted with five different engine families:

1. Pontiac 400 — base/standard Trans Am engine, 1970-1979
2. Pontiac W72 400 — high-output 400, 1977-1979 (the "Bandit-era" performance variant)
3. Pontiac 455 / SD-455 — 1971-1976 standard 455, plus the 1973-1974 Super Duty 455 (the holy grail)
4. Pontiac 301 / 301 Turbo — late-run downsized engine, 1980-1981
5. Oldsmobile 350 (Olds-spec) — yes, Pontiac fitted Olds engines to some 1980-1981 Trans Ams

Each of these has different head bolt torque, different main cap torque, different rod bolt torque, and in some cases (Olds 350, Chevy 305) is mechanically a completely different engine from the others. Identifying which engine is in your specific car is the necessary first step before any torque spec applies.

How to identify your engine

VIN: the 5th character on Pontiac VINs of this era is the engine code. Cross-reference against a Pontiac VIN decoder (the Pontiac Owner's Association maintains a complete table). The VIN tells you what was originally fitted; engine swaps may have occurred since.

Visual identification:

• Pontiac 400 / 455: Unique-to-Pontiac valve covers (10-bolt, distinctive Pontiac shape). Distributor in the rear of the intake manifold. Oil filter on the rear of the block (passenger side). Same general appearance as a Pontiac 350.
• Pontiac 301 / 301T: Smaller-displacement Pontiac architecture, but visibly smaller than the 400/455. Same valve cover and distributor location. The 301T has the turbo plumbing visible on the passenger side of the engine bay.
• Oldsmobile 350: Olds-specific valve covers (different bolt pattern from Pontiac), distributor at the rear, oil filter on the front passenger side of the block. Looks visibly different from a Pontiac 400 if you compare them side-by-side.
• Chevrolet 305 (some 1980 Trans Ams): SBC valve covers (4 bolts each), SBC distributor location. Visually unmistakable as a Chevrolet engine.

Casting numbers on the block (driver's side, just below the deck) confirm engine identity to the part-number level. Pontiac casting numbers, Olds casting numbers, and Chevrolet casting numbers are all easily distinguishable through Pontiac and Olds reference databases (PontiacCity, OldsCarCentral, etc.).

Pontiac 400 (standard Trans Am, 1970-1979)

The canonical Trans Am engine. Head bolt torque, main cap torque, and rod bolt torque values:

• Head bolts: 95 ft-lb final, three passes (50 → 75 → 95)
• Main cap bolts (front): 100 ft-lb final
• Main cap bolts (rear): 120 ft-lb final — this is the famous "rear-main-is-different" Pontiac quirk that catches first-time Pontiac builders
• Rod bolts: 45 ft-lb final
• Intake manifold: 40 ft-lb
• Harmonic balancer bolt: 160 ft-lb (substantially higher than Chevy or Ford — Pontiac uses a heavy fastener)
• Spark plugs: 15 ft-lb (gasketed plugs)

The W72 400 (1977-1979 high-output variant) uses the same bottom-end specs but has a more aggressive cam and unique timing requirements. Verify ignition timing against the W72-specific service literature for your specific year.

SD-455 (1973-1974 Super Duty)

The legendary engine. ~1,300 SD-455 cars were produced total across 1973-1974. The SD-455 has:

• Head bolts: same as 400/455 base spec — 95 ft-lb final, but verify against SD-specific service literature
• Main cap bolts: same architecture as 455 (100 / 120 ft-lb front/rear)
• Rod bolts: 65 ft-lb final — significantly higher than standard 400/455 (45 ft-lb). The SD has heavier rod bolt fasteners for the higher rev limit and higher cylinder pressures.
• The cam, heads, and induction are SD-specific and require the SD service literature for every spec

If you have an actual documented SD-455, you should be working from the SD-specific Pontiac service literature, not generic 400/455 specs. Apply standard 400/455 rod bolt torque (45 ft-lb) to an SD-455 build and the rod bolts will not survive the engine's intended RPM range.

Most SD-455 cars are documented with build sheets and are heavily-pedigreed. If you're working on a 1973-1974 Trans Am that "looks like" an SD-455 but you don't have documentation, verify the engine and casting numbers against the SD-specific reference databases (PontiacCity, Pontiac Historic Services). Hand-built SD clones from non-SD 455 cores are common.

Pontiac 301 and 301 Turbo (1980-1981)

Completely different from the Pontiac 400/455. The 301 is Pontiac's downsized engine for emissions compliance, with a smaller bore and stroke than the 400. The 301T (turbo) added a turbocharger and unique pistons.

• Head bolts (301): ~65-75 ft-lb depending on year and bolt position — verify against the 301-specific service literature
• Head bolts (301T): same bottom-end as 301 but with turbo-specific timing and fueling considerations
• The 301 and 301T are mechanically related to each other but not related to the 400/455

The 301T has unique build challenges — the turbocharger setup is finicky, the engine was emissions-strangled even by 1980 standards, and parts support today is thin. Most 301T owners either preserve the engine carefully or swap to a different drivetrain entirely.

Oldsmobile 350 (some 1980-1981 Trans Ams)

Yes, Pontiac fitted the Oldsmobile 350 V8 to some 1980-1981 Trans Ams. This was a corporate-engine-sharing decision driven by emissions and production realities. The Olds 350 is mechanically an Oldsmobile engine — Olds head bolt torque, Olds main cap torque, Olds rod bolt torque.

• Head bolts (Olds 350): ~100-110 ft-lb final depending on year — verify against Olds service literature
• Main caps: Olds-specific spec
• Rod bolts: Olds-specific spec

Don't apply Pontiac 400 specs to an Olds 350. Different engine entirely.

Chevrolet 305 (some 1980 Trans Ams)

Some 1980 Trans Ams (very late in the second-gen run) got a Chevrolet 305 SBC. This is mechanically the standard Chevy 305:

• Head bolts: 65 ft-lb final on long bolts, 60 on short — same as SBC 350
• Main caps, rod bolts, etc.: standard SBC specs

If you have a Chevy-engined Trans Am, apply SBC specs (see our 1969 Camaro head bolt torque article for full SBC procedure).

Common mistakes

1. Assuming "Trans Am means Pontiac engine." Late-run cars have Olds and Chevy engines fitted from the factory. Verify before doing anything.
2. Applying generic 400/455 specs to an SD-455. SD has unique rod bolt torque (65 vs 45 ft-lb) — get this wrong and the engine fails at high RPM.
3. Forgetting the rear-main-different spec on Pontiac 400/455. Front mains 100 ft-lb, rear main 120 ft-lb. This is unique to Pontiac and catches first-time Pontiac builders.
4. Mixing engine families on the same build. If you've got an Olds 350 in a Trans Am body and you're rebuilding it, use Olds specs. The body says Trans Am; the engine says Oldsmobile.

A reminder on safety

These are research-derived starting values, not factory shop manual data for your specific engine. Always verify against the actual factory service manual for your specific year and engine — the 1970-1981 Trans Am was offered with so many engine families that the very first step on any rebuild is identifying what's actually in the bay. Misidentifying a 301 as a 400 (or applying generic 400 specs to an SD-455) will produce engine failure that costs more than the original mistake.