Getting the torque specs right is critical when installing an intake manifold on a Small Block Chevy, especially the classic Chevy 350 (5.7L V8). Overtightening can crack aluminum castings, while undertightening leads to vacuum leaks and oil consumption.
Whether you are installing a stock replacement or upgrading to a Performance Manifold, this guide covers the exact specs, tightening sequence, and installation tips you need.
Quick Answer: Chevy 350 Torque Specs
| Manifold Material | Torque Specification | Application Notes |
|---|---|---|
| Cast Iron (OEM) | 30 ft-lbs | Standard for older stock engines. |
| Aluminum (Aftermarket) | 20–25 ft-lbs | Recommended for SPELAB Manifolds on Chevy 350. Do not exceed to prevent cracking the aluminum ears. |
| Bolt Size | 3/8"-16 | Standard SBC bolt thread pitch. |
12-Bolt Tightening Sequence (Center-out)
Why center‑out?
Tightening from the middle outward flattens the gasket evenly, prevents manifold warp, and avoids lifted corners that cause vacuum leaks or coolant leaks.
Torque passes
- Pass 1: Snug / 8–10 ft-lbs
- Pass 2: 15–18 ft-lbs
- Pass 3: Final torque (see table above)
Upgrade Your Chevy 350: Single Plane vs. Dual Plane
Since you are installing a new intake, make sure you choose the right performance profile. Are you building a street cruiser or a high-RPM racer? Here is the difference:
Dual-Plane Intake for Chevy 350
RPM Range: Idle - 5,500 RPM
Optimized for the Chevy 350 (5.7L). This 180° design boosts low-end torque and throttle response, making it the perfect upgrade for daily drivers, trucks, and stock engines.
Shop 350 Dual-Plane >
High-Rise Single-Plane for Chevy 350
RPM Range: 3,000 - 7,500+ RPM
Designed for modified SBC 350 engines. Features a large open plenum for maximum airflow at high RPMs. Ideal for drag racing and engines with high-lift cams.
Shop 350 Single-Plane >Step-by-Step Installation Tips
- Clean the Surfaces: Ensure the cylinder head mating surfaces are spotless. Remove all old gasket material.
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Throw Away the End Seals: The cork rubber seals for the front and rear engine block rails (China Walls) are prone to leaking.
Pro Tip: Use a thick bead (1/4 inch) of RTV Silicone instead of the cork gaskets. - Use Thread Sealant: The four center bolts on a Chevy 350 often go into the water jacket/lifter valley. Apply PTFE thread sealer to prevent oil creeping up the threads or coolant leaks.
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The 3-Pass Method: Do not tighten to 25 ft-lbs immediately.
- Pass 1: Snug all bolts to 10 ft-lbs following the sequence.
- Pass 2: Tighten to 18 ft-lbs following the sequence.
- Pass 3: Finish at 20-25 ft-lbs.
Frequently Asked Questions (FAQ)
Q: Do I need to re-torque the intake manifold bolts on my Chevy 350?
A: Yes. Aluminum intake manifolds expand and contract differently than the cast iron heads found on most Chevy 350s. We recommend re-torquing the bolts after the engine has gone through one full heat cycle (reached operating temp and cooled down completely).
Q: Why choose Aluminum over Cast Iron for a Chevy 350?
A: Weight and Heat. A Aluminum Manifold saves about 15-20 lbs off the front end of your car. Aluminum also dissipates heat faster, keeping the intake charge cooler for better power.
Q: Will these manifolds fit my Vortec 350 heads?
A: No. These specific manifolds fit 1955-1986 SBC cylinder heads (Pre-Vortec) with the traditional 12-bolt pattern. 1996+ Chevy 350 Vortec heads use a different 8-bolt pattern.
Q: Can I use a stock carburetor with these manifolds?
A: SPELAB manifolds feature a standard 4150 Square Bore flange. If your Chevy 350 has a stock Quadrajet (Spread Bore), you will need a simple adapter plate.
