Chevy 350 Exhaust Manifold Torque Sequence Diagram
Chevy 350 exhaust-manifold center-out sequence with L31 11/22 lb-ft passes, Hooker header branch, gasket preparation and application limits.
For the cited 1998 Chevrolet K1500 L31 5.7L production manifold, tighten the six fasteners on each bank from the center pair outward: with one bank drawn left to right, the physical order is 5-3-1-2-4-6. Make a first pass at 15 N-m (11 lb-ft) and a final pass at 30 N-m (22 lb-ft). Do not treat that as a universal 350 value. Hooker's cited 1975-1981 F-body small-block headers use six supplied bolts per bank and specify 25-30 lb-ft for that product, while replacement heads and other headers can publish another value.
Chevy 350 Gen I / L31 exhaust hardware cannot be reduced to one internet torque number. Cast-iron production manifolds, tubular headers, replacement cylinder heads and revised service bolts can share the same engine family while using different flange thickness, washers, coatings and gasket compression. The reliable process begins by identifying the exact vehicle and installed parts, then selecting one complete instruction branch.
GM's L31 service record gives a two-pass 11/22 lb-ft procedure for the 1998 K1500 VIN R. That is a late Vortec Gen I truck application, not proof that every Chevrolet 350 used those same bolts or gasket.
The interactive diagram is a clamping-order aid, not permission to merge specifications. Its purpose is to distribute load from the center of a matching flange toward the ends. The documented comparison values on this page are 1998 L31 first pass: 15 N-m / 11 lb-ft; 1998 L31 final pass: 30 N-m / 22 lb-ft; Hooker 1975-81 F-body: 25-30 lb-ft; Typical bank count: 6 fasteners. Use only the row supported by the vehicle service information or the instructions supplied with the manifold, header, gasket and cylinder head.
Interactive Chevy 350 six-fastener center-out map
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One bank, viewed from the exhaust side. Physical labels read 5-3-1-2-4-6 from end to end; tighten numerically 1 through 6. Use the torque branch for the exact vehicle or header.
Chevy 350 Exhaust Manifold Torque Sequence Diagram
| APPLICATION / ITEM | SPECIFICATION | NOTES |
|---|---|---|
| 1998 L31 first pass | 15 N-m / 11 lb-ft | Six-fastener production manifold |
| 1998 L31 final pass | 30 N-m / 22 lb-ft | Repeat same center-out order |
| Hooker 1975-81 F-body | 25-30 lb-ft | Supplied six-bolt header branch only |
| Typical bank count | 6 fasteners | Verify the installed head and flange |
The L31 Vortec 350 service branch and a traditional earlier Gen I 350 may share six exhaust positions per bank, but head material, bolt style, manifold/header flange and gasket determine the final clamp rule. The diagram is a center-out map; the selected source determines passes, lubricant/thread treatment and any recheck.
How to use this specification correctly
- 01
Record the vehicle year, platform, engine code and cylinder-head identification. Photograph the installed Chevy 350 Gen I / L31 manifold or header and record its part number before ordering gaskets or bolts.
- 02
Work only on a cold exhaust system. Disconnect the negative battery cable, support the vehicle at approved lifting points and use eye protection; rust, penetrating fluid and broken fasteners create hazards above and below the engine.
- 03
Label oxygen-sensor connectors, heat shields, dipstick brackets, EGR/AIR tubes and plug-wire or coil locations. Support the front pipe or converter so its weight cannot pull on the manifold flange or oxygen-sensor wiring.
- 04
Loosen the head fasteners progressively from the ends toward the center. A stuck or corroded bolt should be treated with the application-appropriate extraction method; forcing it sideways risks breaking it below the cylinder-head surface.
- 05
Remove the manifold and gasket, then protect every exhaust port. Clean the sealing faces without gouging aluminum or cast iron, chase only repairable threads and inspect the flange with a straightedge for warpage, cracks and eroded sealing beads.
- 06
Match the new gasket to the ports, bolt holes and marked orientation. Keep the gasket dry unless the component manufacturer explicitly specifies a coating; generic silicone at an exhaust port can burn, contaminate sensors or prevent even seating.
- 07
Return special studs, stainless bolts, spacers, tie bars, washers and brackets to their documented locations. Hand-start every head fastener several turns and leave the outlet connection loose enough that the manifold can seat without exhaust-system side load.
- 08
Snug the matching flange from its center toward the ends. Follow the interactive order only when the physical fastener count and source branch match; otherwise use the side-specific factory or component diagram supplied for the exact part.
- 09
Make the specified passes with a calibrated low-range torque wrench. Do not add threadlocker, anti-seize or oil unless the selected procedure includes it because thread friction changes bolt stretch at the same wrench reading.
- 10
Align and tighten the outlet joint and supports only after the head flange is seated. Reconnect sensors and shields, start the cold engine, listen for a sharp tick and inspect for escaping gas; perform any heat-cycle recheck only if the selected instructions require it.
Choosing the correct torque branch
GM's L31 service record gives a two-pass 11/22 lb-ft procedure for the 1998 K1500 VIN R. That is a late Vortec Gen I truck application, not proof that every Chevrolet 350 used those same bolts or gasket.
The Hooker F-body sheet uses six supplied bolts on each bank and 25-30 lb-ft. That higher product-specific range belongs to its header flange and hardware. Chevrolet's 350 HO guide also warns installers to verify straight-plug clearance and use application service information.
How to use the sequence diagram
The numbered map represents tightening order. On a matching six-fastener flange, the physical labels read 5-3-1-2-4-6 from one end to the other, so numerical tightening begins in the center and expands outward. This minimizes bending while the gasket is compressed.
Use the same order for each specified pass. Mark a completed position with a paint pen or worksheet rather than relying on memory, especially when steering, frame or accessory clearance forces several extensions and wrench angles.
Fasteners, gaskets and friction condition
A factory cast-iron manifold, thin tubular header and thick laser-cut header flange react differently as they heat. Inspect the flange against a straightedge and confirm that the gasket's sealing bead surrounds every port without hanging into the gas path.
Accessory brackets and dipstick supports may share exhaust fasteners. Their thickness changes available thread engagement, so return each bracket to its original position and use the bolt length supplied or specified for that location.
What the cited sources actually establish
The L31 record establishes the two torque passes. Flowmaster's flange guidance supports the general inside-out load path but explicitly says the exact sequence varies by flange. The diagram therefore shows a conventional six-position center-out controller rather than claiming one vintage drawing fits every 350.
Hooker's sheet establishes only its named header branch. If a different brand supplies locking bolts, special washers or a lower torque for aluminum heads, that instruction supersedes the Hooker value.
Diagnosing an exhaust leak after installation
- A cold-start tick that fades as parts expand commonly points to a head-flange or cracked-manifold leak.
- Black soot at one port identifies escaping gas but does not prove the bolt needs more torque; inspect flatness and the gasket.
- A leak at the outlet flange can sound like a head leak, especially when the front pipe is pulling sideways.
- A broken end bolt often accompanies a warped production manifold; replacing only the bolt can lead to another failure.
- An oxygen-sensor fault after service may come from a disconnected harness, damaged wire or upstream air entering through a leak.
- Do not search for a leak by touching a running manifold or by spraying flammable liquid on hot exhaust parts.
Chevy 350 Gen I / L31 exhaust-manifold checklist
- Year, platform, engine code and head material confirmed
- Production manifold versus aftermarket header identified
- Part number and fastener count matched to instructions
- Engine and exhaust system completely cold
- Vehicle and front pipe safely supported
- Sensors, tubes, brackets and shields labeled
- Broken bolts and damaged threads repaired correctly
- Head and flange checked for cracks and warpage
- Correct new gasket fitted in the marked orientation
- Special studs, washers, spacers and tie bars returned to position
- Every fastener hand-started
- Center-out passes completed without mixing torque branches
- Outlet joint aligned before final tightening
- Cold-start leak check completed
- Required heat-cycle recheck recorded
Chevrolet Chevy 350 Gen I / L31 specifications can change by model year, engine, platform, wheel, and installed component. Confirm the VIN or engine identity, part numbers, fastener condition, and the current manufacturer instructions before service.
Chevy 350 Exhaust Manifold Torque Sequence Diagram FAQs
What is the 1998 Chevy 350 L31 exhaust-manifold torque?+
For the cited K1500 VIN R, use 15 N-m (11 lb-ft) first and 30 N-m (22 lb-ft) final in sequence.
What is the six-bolt Chevy 350 exhaust sequence?+
For the center-out controller, physical positions read 5-3-1-2-4-6 from one end of the bank to the other, and tightening proceeds numerically 1 through 6.
Are header bolts also 22 lb-ft?+
Not necessarily. The cited Hooker 1975-1981 F-body kit specifies 25-30 lb-ft with its supplied six-bolt hardware.
Should exhaust-manifold bolts be tightened from the center outward?+
That is the documented direction for the center-out branches on this page. Use the exact side-specific figure when the service manual numbers individual positions or the flange has more than the illustrated six fasteners.
Can I use the stock manifold torque on headers?+
Not automatically. Header flange thickness, bolt/washer design, gasket and cylinder-head material can require a different value and recheck schedule. Follow the header manufacturer's instructions.
Should I put anti-seize on the bolts?+
Only when the selected instruction specifies it. Anti-seize changes friction and can increase clamp load at the same torque. GM's cited updated-bolt procedure instead specifies a particular high-temperature high-strength threadlocker.
Why did an end bolt break?+
Thermal movement, a warped manifold, outlet-pipe stress, corrosion, incorrect hardware or uneven tightening can overload an end fastener. Inspect the complete joint rather than replacing the bolt alone.
Do exhaust-manifold bolts need retorquing after a heat cycle?+
Only if the vehicle, head, header or gasket instructions call for it. Some Ford and aftermarket procedures do; other production procedures specify a completed cold two-pass installation without an added hot check.
Technical sources
TorqueSheet favors engine- and component-specific manufacturer instructions over unsourced universal values.
1Chevrolet Performance 350 HO Deluxe engine guideChevrolet identifies the current 350 HO's straight-plug cast-iron heads, warns that manifold/header clearance is installation-specific and directs builders to the application service manual.↗2Hooker BlackHeart 1975-1981 GM F-body small-block header instructionsHolley's application sheet documents six supplied header bolts per bank, 25-30 lb-ft, gasket inspection and the surrounding steering, dipstick, plug and exhaust-system work for its named product.↗3Flowmaster header installation and flange-tightening guidanceThe component maker directs installers to start inside the flange and work outward, alternating to draw the flange evenly, while noting that the exact sequence varies by flange.↗