944 Exhaust System — Layout, Flanges & Torques
Factory data for the 944 exhaust system — the three flanged joints from the manifold back to the final muffler, the single M8 tightening torque that applies to every flange, and the factory method for replacing the exhaust pipe, primary muffler or catalytic converter by welding a sleeve into the pipe.
Factory data for the 944 exhaust system. The system runs from the exhaust manifold at the cylinder head, through the exhaust pipe and the primary muffler (a catalytic converter takes the primary muffler's place on cars fitted with one), to the final muffler at the rear. The joints between these sections are bolted flanges, and the whole system is held together by a single fastener size — so there is only one tightening torque to remember. For removing and installing the complete system, and for the turbo crossover-pipe arrangement, see Exhaust System Removal and Installation.
Flange joints and torque
The system has three flanged joints. Checking them for tightness is a routine service item — a loose flange leaks exhaust and rattles.
- Hexagon nuts at the exhaust manifold / cylinder head joint.
- Hexagon nuts at the exhaust manifold / primary-muffler flange.
- Hexagon nuts at the primary muffler / final-muffler flange.
Every flange on the system uses M8 bolts and nuts, and they all take the same torque:
| Fastener | Tightening torque |
|---|---|
| M8 bolts and nuts (all exhaust flanges) | 20 N·m15 ft·lb |
Tip: Because the flanges see repeated heat cycling, treat a flange that will not hold torque as a sign of a stretched stud, a crushed gasket or a warped flange face — not just an under-tightened nut. Renew the flange gaskets whenever a joint is opened.
System layout
The section between the manifold and the final muffler is built from three parts:
| No. | Part | Qty |
|---|---|---|
| 1 | Exhaust pipe | 1 |
| 2 | Sleeve | 1 |
| 3 | Primary muffler | 1 |
The sleeve (2) is the key to the factory repair method below: rather than replacing the exhaust pipe as a whole unit, the pipe is cut and a new section is joined to it with a welded sleeve.
Replacing the exhaust pipe, primary muffler or catalytic converter
The primary muffler — or the catalytic converter that replaces it on cars so equipped — is served as a unit with a stub of exhaust pipe. To fit a replacement, the old pipe is sawn off and the new one is joined with the welded sleeve so the finished assembly sits without stress on the car.
- Remove the complete primary muffler (or catalytic converter). Mark the cutting point 70 mm from the flange and saw off the exhaust pipe, with the cut plane perpendicular to the pipe axis.
- Mount the new parts on the car, using the old gaskets and nuts for this trial fit.
- Align the exhaust assembly with the connecting sleeve so it sits without stress, then tack-weld the sleeve at several points to hold everything in the installed position.
- Remove the exhaust assembly from the car and weld the sleeve all the way around.
- Refit using new gaskets and new mounting nuts for the final installation.
Caution: The dry-fit in step 2 uses the old gaskets and nuts on purpose — do the final weld with the parts off the car, then reassemble with new gaskets and new nuts so the flange joints seal and hold torque. Never make the full weld with the assembly still hanging on the car, where you cannot check it for stress-free alignment.