Description

Akrapovič Slip-On Porsche 911 Turbo / Turbo S (991)

Akrapovič Slip-On Integration with OEM Rear Diffusers

Models: Porsche 911 Turbo / Turbo S (991 and 991.2)
Systems concerned: Akrapovič Slip-On Line (Titanium)

1. Porsche 911 Turbo / Turbo S (991, MY2013–2015)

• OEM diffuser reference: 991.505.311.08 (standard black polymer).
• Material: glass-fiber reinforced polyamide (PA6-GF30), thermal resistance ~180–200°C continuous, 230°C short peak.
• Geometric mismatch: Akrapovič dual-round outlets (Ø95 mm) are positioned 6–8 mm higher relative to the stock oval aperture axis. With the OEM diffuser, this produces reduced clearance at the upper edge of the outlet (≤ 3 mm versus the 8–10 mm designed tolerance).
• Thermal implication: insufficient convective evacuation leads to local hot spots reaching ~210–220°C under sustained load, which exceeds the long-term thermal stability of the polymer substrate. Risk: progressive discoloration, softening, or surface deformation.
• Structural load path: the stock diffuser does not provide lateral or vertical support for the larger-diameter pipes, meaning all reaction forces are absorbed by the silencer brackets (Porsche PN 991.111.252.91). This increases static bending moment by ~12–15% compared with OEM geometry.

Recommendation: The Akrapovič carbon diffuser (matte PN DI-PO/CA/7/M, gloss PN DI-PO/CA/7/G) restores 360° clearance around outlets, introduces airflow channels that reduce thermal accumulation, and provides secondary positional stability to the tailpipe assembly.

2. Porsche 911 Turbo / Turbo S (991.2, MY2016–2019)

• OEM diffuser reference: 991.505.311.10 (standard), 991.505.311.11 (SportDesign).
• Material: identical polymer specification to pre-facelift; however, diffuser geometry was modified to integrate with revised active aero ducts.
• Geometric mismatch: outlet apertures narrowed by 4–5 mm per side and offset by 2° relative to the horizontal axis. When combined with the Akrapovič Slip-On (Ø95 mm pipes), this produces asymmetry in clearance: ≤ 2 mm at the upper inner edge vs. 9 mm at the lower outer edge.
• Thermal implication: CFD simulations performed by independent tuners show stagnation zones forming at the upper edge, with temperature spikes exceeding 230°C under track load. This crosses the maximum polymer tolerance and risks localized warping after repeated heat cycles.
• Structural load path: lack of diffuser guidance allows increased lateral oscillation amplitude of ~0.7 mm under resonance frequencies (2,000–2,400 rpm), transferring cyclical bending to the silencer mounting sleeves. Long-term effect: accelerated wear of isolator bushings, leading to potential rattling or misalignment.

Recommendation: The Akrapovič 991.2-specific carbon diffuser (PN DI-PO/CA/8/M or DI-PO/CA/8/G) aligns outlet geometry to within ±1 mm tolerance, maintains uniform 7–9 mm clearance on all edges, and integrates a carbon-composite reinforcement rib. This ensures both thermal and vibrational stresses remain within the design envelope of the Slip-On system.