BNS vs S65B40/44 - How Do They Compare

BNS

The BNS includes:

A two-piece closed deck cylinder block
90 degree V angle
42CRMOS4 forged crankshaft
34CRNIMO8 split conrods
Forged aluminium pistons
Chain-driven DOHC
Four valves per cylinder with roller rocker arms and hydraulic lifters
FSI direct fuel injection (Fuel Stratified Injection)
4-2-1 exhaust manifold
Compression ratio of 12.5:1
A length of 464 mm
A height of 228 mm.

The BNS is based on the BAR engine found in the Q7 4L, but has loads of modifications which include increased crankcase breathing, a low-pressure fuel return system and a baffled oil sump to prevent engine lubricant cavitation at high engine speeds and high G force cornering. It has 84.5 mm bores spaced at 90 mm intervals, and a 92.8 mm stroke for a capacity of 4163 mm, while the cylinder banks had an 18.5 mm offset. The bores were made in a three-stage honing and exposure process. The silicon grains in the cylinders were removed to provide the necessary wear resistance of the cylinder surfaces for the pistons and piston rings. Before the honing began, a honing template was attached to the crankcase in order to test the warping effect of the cylinder manifold. The lower crankcase was made from aluminium which included iron main bearing covers made of cast iron. As mentioned above, the BNS had a die-forged crankshaft that was made of high-alloy tempered steel (42CrMoS4) and rotated on five bearings. The main bearings had a 18.5 mm width and a 65.0 mm diameter while the big-end bearings were 15.25 mm wide and with a 54.0 mm diameter. In order to reduce unwanted engine vibration, heavy metal inserts were integrated in the first and eighth crank journals by way of unbalance. And it also had a dual-mass damper to prevent vibrations at high RPM.

The BNS engine had split connecting rods that were made of 34CrNiMo8. And unlike the BAR engine it was based on, the geometry and tolerances for the connecting rods were reduced for the BNS engine. The connecting rods were 154 mm long, had 54 mm diameter bearing journals, as well as 1.4 mm thick and 15.25 mm wide bearing bushings. It had forged aluminium pistons with Ferrostan-coated skirts in order to prevent direct contact between the pistons and the cylinder walls. The piston crowns were also adapted for direct injection and circular air flow in the cylinder. Each piston weighed around 290 grams.
The aluminium cylinder head and double overhead camshafts were connected through a hydroforming
process. The camshafts were driven by 3/8 simplex sleeve-type chains due to their low wear and high stress resistance properties. Chain tension was maintained by hydraulic tensioners and the chain drive was maintenance free and designed for the life of the engine. It had four valves per cylinder that were actuated by roller finger cam followers including hydraulic backlash compensation. The intake and exhaust valves had chrome-plated stems that were filled with sodium for heat dissipation, and the valve lift was 11.0 mm. Compared to the BAR engine, the BNS’ intake valve opening angle was 230 crank degrees and the exhaust valve opening angle was 220 degrees. Both the intake and exhaust camshafts had an adjustment range of 42 degrees while maximum valve overlap was 47 degrees.

The engine map-controlled intake manifold flaps that were used only at lower engine speeds. When activated, the intake manifold flaps were brought into contact with the port baffles located in the cylinder head to seal the lower part of the intake port. The air mass would flow through the upper section of the intake and induce a tumbling, charging motion inside the cylinder. When they weren’t used, the open intake manifold flaps would maximise the cross-sectional area of the port. The intake manifold flaps were activated by one vacuum actuator per cylinder bank. But unlike the BYH/CNDA engine from the R8 V8, the BNS didn’t have a dry sump lubrication system.

S65

It was based on the larger S85B50 V10 engine rivalling Audi’s BUH engine, and replaced the older, heavier S54B32 inline 6 engine from the E46 M3. It had a 92.0 mm bore and a stroke of 75.2 mm providing a capacity of 3998 cc, the limited production E90 M3 CRT and E92 M3 GTS models used the larger S65B44 with a stroke of 82.0 and a capacity of of 4361 cc. It had a wet-sump lubrication system with an oil return pump, with a main oil pump replacing the system used on the S85, which decreased weight. The alternator disconnects from the engine during acceleration to maximise power, only charging the battery during braking when possible, BMW calls it Brake Energy Regeneration. The S65 weighed 202 kg, and was also shorter than the S54 since it was a V shaped engine.

Just like the S85, the S65 engine had a two-piece Alusil crankcase with a reinforcing bedplate. The bedplate was machined together with the crankcase, and when the engine was assembled, the bedplate was mounted to the upper section of the crankcase. The bedplate assembly contained cast iron bearing bridges to absorb additional forces from the pistons and connecting rods. The upper crankcase was of aluminium-silicon alloy, while the lower bedplate was made from die-cast aluminium, though grey cast iron inlays were used to reinforce the bedplate construction. And the cylinder bores were formed using exposed hard silicon crystals such that cylinder liners were not required. The cylinder heads for the S65 were produced from a single piece of aluminium. The double overhead camshafts (DOHC) had hollow-cast, one-piece construction with integrated sensor gears. While the
variable intake and exhaust cam timing (VANOS) operated at normal oil pressure compared to the high pressure operation of the S85B50 engine. The inlet camshafts were chain-driven, while the exhaust camshafts were driven by a gearwheel drive. It also had two double roller chains between the crankshaft and the inlet camshaft. And the valves were actuated by hydraulic bucket tappets.

The S65 engine had a 4-1 exhaust manifold in each cylinder bank, and the exhaust pipes were made using internal high pressure forming at pressures of up to 800 bar (11603 psi). The wall thickness for the stainless steel exhaust pipes was between 0.65 and 1.0 mm. The S65 engine had port injection and operated at a compression ratio of 12.0:1, which was a tiny bit lower than Audi’s BNS engine. And unlike the 1-5-4-8-6-3-7-2 cylinder firing order used for most of BMW’s V8 engines, the order for the S65 engine was 1-5-4-8-7-2-6-3 and the ignition was controlled by the Siemens MSS60 engine management system.
It had a five-bearing crankshaft that was forged from a single piece., and It also included high tensile steel conrods split by fracture separation, and the upper section of the connecting rod had a trapezoidal shaped cross-section as well as the aluminium alloy cast pistons with.

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