Removal and replacement of the exhaust downpipe (front exhaust pipe) connecting the exhaust manifolds to the intermediate pipe on a 1966 Corvette 327 V8.

Warnings

Tools required

Parts

• Exhaust downpipe assembly × 1 — Use OEM specification or quality aftermarket
• Exhaust manifold flange gaskets × 2 — Use OEM specification
• Intermediate pipe flange gasket × 1 — Use OEM specification
• Exhaust flange nuts (3/8"-16) × 8 — Use OEM specification or Grade 8
• Exhaust flange bolts × 4 — Use OEM specification or Grade 8

Preparation

1. Ensure engine and exhaust system are completely cold
2. Park vehicle on level ground and engage parking brake
3. Place wheel chocks behind rear wheels
4. Raise front of vehicle with floor jack and support securely on jack stands under frame rails
5. Spray all exhaust flange nuts and bolts with penetrating oil and allow to soak for at least 30 minutes (overnight preferred for heavily corroded fasteners)
6. Verify adequate working clearance under vehicle
7. Disconnect negative battery cable if working near starter or electrical components

Procedure

1. 1

   Access the exhaust system
   Position yourself under the vehicle with adequate lighting. Locate the downpipe assembly which connects the exhaust manifolds to the intermediate exhaust pipe. The downpipe is a Y-shaped pipe with two inlet flanges (one per exhaust manifold) and one outlet flange connecting to the intermediate pipe.
2. 2

   Disconnect oxygen sensor (if equipped)
   The 1966 Corvette is not equipped with an oxygen sensor. Skip this step — no oxygen sensor exists in the downpipe or exhaust system on this carbureted vehicle.
3. 3

   Remove intermediate pipe connection
   Locate the flange connection where the downpipe connects to the intermediate pipe (typically below the transmission crossmember). Remove the 2 flange bolts or nuts securing this connection using a 1/2" socket and ratchet. The connection may be stuck due to carbon buildup; use a pry bar or exhaust flange spreader to separate if necessary.
4. 4

   Remove left exhaust manifold connection
   Locate the left (driver side) exhaust manifold flange where the downpipe connects. Remove the flange nuts securing the downpipe to the exhaust manifold using a 9/16" socket or wrench. Note the actual fastener count for your specific manifold flange (typically 2 per side) and keep all hardware organized. Keep track of any washers or spacers present.
5. 5

   Remove right exhaust manifold connection
   Locate the right (passenger side) exhaust manifold flange. Remove the flange nuts securing the downpipe to the exhaust manifold using a 9/16" socket or wrench. Note the actual fastener count for your specific manifold flange (typically 2 per side). Note the position of any heat shields or brackets that may be attached.
6. 6

   Remove downpipe assembly
   With all fasteners removed, carefully maneuver the downpipe assembly downward and out from under the vehicle. The pipe may be wedged in position due to years of thermal cycling; use a dead blow hammer to tap flanges loose if needed. Be prepared for carbon deposits and rust to fall during removal.
7. 7

   Clean all mating surfaces
   Using a wire brush and scraper, thoroughly clean all exhaust flange mating surfaces on both exhaust manifolds and the intermediate pipe. Remove all old gasket material, carbon deposits, and rust. Clean surfaces ensure proper sealing and prevent exhaust leaks.
8. 8

   Inspect exhaust manifold studs
   Inspect all exhaust manifold studs for damage, corrosion, or looseness. If any studs are broken, stripped, or loose in the manifold, they must be replaced or repaired before proceeding. Run a thread chaser over intact studs to clean threads.
9. 9

   Install new gaskets on exhaust manifolds
   Position new exhaust manifold flange gaskets onto the left and right exhaust manifold flanges. The gaskets should fit over the studs and sit flush against the manifold face. Use a small amount of anti-seize on studs if desired to ease future removal.
10. 10

    Position new downpipe assembly
    Carefully maneuver the new or cleaned downpipe assembly into position under the vehicle. Align the two inlet flanges with the exhaust manifold flanges first, ensuring gaskets remain in position. The intermediate pipe outlet should align approximately with the connection point.
11. 11

    Install exhaust manifold flange fasteners
    Thread new flange nuts onto the exhaust manifold studs for both left and right sides (3 nuts per side). Start all 6 nuts by hand before tightening any. Tighten in a crossing pattern to draw flanges evenly. Final tightening should be snug but not over-torqued; 3/8" exhaust flange nuts typically require approximately 20-25 ft-lbs, but verify the factory specification for this application.
12. 12

    Connect intermediate pipe flange
    Position a new flange gasket between the downpipe outlet and intermediate pipe inlet. Align the bolt holes and install the 2 flange bolts with washers. Tighten evenly in a crossing pattern until the flange connection is secure with no gaps visible.
13. 13

    Reinstall oxygen sensor (if equipped)
    The 1966 Corvette has no oxygen sensor to reinstall. Skip this step.
14. 14

    Verify clearances and routing
    Before lowering the vehicle, verify that the downpipe has adequate clearance from the transmission, crossmember, frame rails, and steering components. The pipe should not contact any chassis components and should have at least 1/2 inch clearance at all points to allow for thermal expansion and engine movement.

Reassembly

1. Lower vehicle from jack stands carefully
2. Reconnect negative battery cable if disconnected
3. Remove wheel chocks

Verification

• Start engine and allow to reach operating temperature while monitoring for exhaust leaks at all flange connections
• Listen for any exhaust ticking or hissing sounds that indicate gasket leaks
• Visually inspect all flange connections for signs of escaping exhaust gases (soot buildup or visible smoke)
• Check for proper exhaust flow from tailpipe outlet
• Verify no exhaust components contact chassis or body during engine operation
• Test drive vehicle and verify normal exhaust sound with no rattles or unusual noises
• Re-check all flange connections after 50-100 miles of driving and re-tighten if necessary

More procedures for this vehicle