Sav Gualtieri built his BMW F30 335i at his company SavSpeed in South Africa. The car was previously powered by a turbocharged 3.0 L inline-six making 800 hp (596 kW). Eventually Sav swapped that for a turbocharged 4.0 L S65 V8 capable of 1300 hp (969 kW) on 1.3 bar (18.8 psi) of boost. The motor features forged rods and pistons, custom exhaust manifolds, large turbocharger, and Syvecs S7-Plus standalone ECU. Behind that is M3 E92 manual transmission and differential. Watch Sav take on Simola HillClimb in the video below.
Source: HillClimb Monsters and SavSpeed Auto FB page