Nova I6 250 vs SBC 350 Head Bolt Torque (1968-1974)

The numbers

For 1968-1974 Chevrolet Novas with iron heads and factory bolts:

• 250 / 230 inline-six head bolt torque: 95 ft-lb final
• 307 / 327 / 350 SBC head bolt torque: 65 ft-lb on long bolts, 60 ft-lb on short bolts

These are very different specs despite both engines being in the same body. Apply the wrong spec and you'll either under-torque the head (gasket failure) or over-torque (stretched bolts, damaged threads). Identifying which engine is in your Nova is the first step before any torque spec applies.

Why the I6 needs more torque

The Chevrolet inline-six (the 230, 250, and 292 family) is a long-deck engine — substantially taller than the V8. The head bolts span more material and need more clamp load to seat the head correctly against the block. The SBC 350 has a shorter, more compact head architecture with shorter bolts that don't need as much torque.

This is the same logic that makes the Pontiac 400 use 95 ft-lb on its head bolts (also a long-deck design relative to the SBC) and the Ford 351W use 105 ft-lb (yet another long-deck variant). Long-deck engines need more head bolt clamp load, period.

Identifying which engine you have

The fastest way to tell an SBC from a Chevrolet I6 in a Nova:

• Cylinder count visible from above. SBC has eight spark plug wires. I6 has six. This is the easiest visual identifier.
• Head and valve cover length. I6 valve cover is much longer (nearly the full length of the engine bay on the passenger side); SBC valve covers are split into a left and right cover, each shorter.
• Distributor location. Both have rear-mounted distributors, but the I6 distributor sits noticeably higher on the engine.
• Engine length. The I6 is roughly 28-30" long; the SBC is roughly 20" long. From above, the I6 occupies most of the engine bay.

If you're unsure (rare on a Nova — the difference is obvious), the casting numbers on the block are definitive. Chevrolet I6 casting numbers are different from SBC casting numbers; cross-reference against a Chevrolet engine identification database.

SBC 350 sequence and procedure

For the 350 SBC (and 307/327 — same architecture):

• Final torque: 65 ft-lb on long bolts, 60 ft-lb on short bolts
• Sequence: center outward, three passes (35 → 50 → final)
• Lubricant: engine oil on threads

(See our 1969 Camaro head bolt torque article for the full SBC procedure — same engine architecture appears in 1968-1974 Novas.)

I6 250 sequence and procedure

For the 250 inline-six (and 230 — same architecture):

• Final torque: 95 ft-lb on all bolts (the I6 doesn't have the long/short distinction the SBC has)
• Sequence: center outward, three passes (50 → 75 → 95 ft-lb)
• Lubricant: engine oil on threads

The I6 has fewer head bolts than the V8 — typically 14 head bolts on the inline-six versus 17 per side on the V8 (plus the longer span). The pattern is straightforward center-outward.

Bottom-end and accessory specs (250 I6)

For completeness on a 250 I6 rebuild:

• Main cap bolts: 75-80 ft-lb final
• Rod bolts: 35 ft-lb final (lower than SBC because the I6 rod design uses a smaller fastener)
• Intake manifold bolts: 30 ft-lb (the I6 intake is shorter than the SBC and uses fewer bolts)
• Spark plugs: 15 ft-lb (gasketed plugs)
• Harmonic balancer: 60 ft-lb
• Flywheel: 60 ft-lb
• Valve cover: 90 in-lb
• Lug nuts (Nova): 80 ft-lb (factory 5x4.75 pattern)

Verify against the specific year's Nova service manual.

When to deviate

Use the head/hardware manufacturer's spec instead if you're running:

• Aftermarket aluminum heads (SBC): AFR, Dart, Edelbrock, etc. — typically 65-70 ft-lb with manufacturer-specific lubricant.
• Aftermarket aluminum heads (I6): Clifford Performance and a few others make aftermarket I6 heads — verify against their specific recommendation.
• ARP studs (any engine): follow ARP's instructions exactly.
• Stroker or built engine — use the engine builder's spec from their build documentation.

Common mistakes

1. Applying SBC specs to a 250 I6. Wildly under-torques the head; gasket fails within a few hundred miles. The most common mistake on Nova I6 rebuilds.
2. Applying I6 specs to an SBC. Over-torques the head; can pull threads in the block.
3. Mixing factory and aftermarket bolts in the same head. Replace the entire set if any single bolt fails inspection.
4. Skipping the three-pass sequence. Going straight to final torque distorts the head.
5. Anti-seize on threads. Reduces friction and over-torques the bolt by 20-30%.

I6 250 — is it worth keeping?

Many Nova owners eventually consider swapping the 250 I6 to a small-block V8 because the SBC is more powerful, has better aftermarket support, and is easier to source rebuild parts for. That's a personal call:

• Keep the I6 if your Nova is documented original and the engine is the original-build engine. Original 250-equipped Novas have specific value to enthusiasts.
• Keep the I6 if you want to do something interesting — aftermarket aluminum heads (Clifford), turbocharged 250 builds, or a stroker 292 with a forged crank.
• Swap to SBC 350 if you just want a reliable small-block V8 in a Nova body. The swap is straightforward, parts are everywhere, and the resulting car is mechanically equivalent to a factory V8 Nova.

A reminder on safety

These are research-derived values, not factory shop manual data for your specific engine. Always verify against the actual factory service manual for your specific year and engine — head bolt torque is a failure mode that destroys engines silently. The SBC vs I6 spec difference (60 ft-lb difference) is large enough that getting it wrong reliably blows the head gasket.