The 2.0-litre turbocharged B48 (B48A20) engine in the F40 M135i xDrive is a potent 4-cylinder powerplant, but extracting extreme horsepower figures or fitting larger hybrid turbochargers requires a heavily reinforced internal architecture. High cylinder pressures generated by aggressive tuning can quickly exceed stock internal limits. Fortify your B48 block with heavy-duty Forged Pistons and ultra-strong Forged Connecting Rods/Conrods. Secure your rotating assembly with high-tensile Upgraded Engine Bolts (ARP) and drastically reduce internal friction using race-spec Performance Bearings (Conrod & Mains). Ensure a flawless seal across your engine block and cylinder head with upgraded Engine Gaskets.