300hp + piston engine ASE-650 Saga

for general aviation4-stroke12-cylinder

Overview
The ASE-650 Saga is a low-volume converted aircraft powerplant based on the BMW M73-B54 5.4 L V12. Designed and produced by Aerosport Engineering AS for experimental and kit aircraft, the conversion targets continuous high-load operation with an emphasis on predictable behavior and serviceability.

Important aircraft engine properties
The ASE-650 Saga prioritizes reliability and safety while maintaining a competitive power-to-weight ratio and reasonable fuel efficiency for sustained flight operations. The unit is intended for operators seeking a carefully modified automotive base engine adapted for aircraft duty.

Conversion rationale and base engine choice
The conversion uses the BMW M73-B54 aluminium 60° V12 block (1991–2003). The AluSil block with NicaSil-coated cylinders and a simplified valvetrain make the M73 a suitable platform for extensive adaptation to continuous high-load aviation use.

Key built-in features

• NicaSil coated cylinder liners to improve cylinder wall durability under continuous high load
• SOHC valvetrain with factory roller lifters—chosen to avoid Vanos/Valvetronic complexity
• Piston oil cooling nozzles aimed at continuous underside piston cooling for thermal safety

Complexity and design philosophy
The design deliberately favors mechanical simplicity over variable automotive systems. By avoiding variable valve timing and lift systems, the ASE-650 Saga delivers a robust valvetrain and ignition approach suited to near-constant RPM operation typical of aircraft service.

Combustion and Lambda considerations
Aircraft continuous-high-load operation requires richer air/fuel ratios than automotive Lambda‑1 targets. The conversion includes fuel and ignition tuning tailored to avoid detonation and control temperatures during prolonged high-load cruise and climb phases.

Ignition cycle and V12 configuration
The engine keeps a 60° V layout with a 120° crankshaft to obtain even-fire spacing (ignition every 60° of crank rotation). Even-fire sequencing improves torque balance and reduces torsional excitation associated with odd-fire conversions.

Performance and design limits
The ASE-650 Saga is tuned for conservative maximum RPM and moderate boost to preserve durability. The specified maximum for routine service is 5000 RPM to limit mean piston speed and extend component life.

RPM / Power / Torque / Boost (performance data)
3000 RPM — 304 Hp — 532 Lb-ft / 723 Nm @ 10.4 Psi / 0.73 Bar
3200 RPM — 340 Hp — 559 Lb-ft / 760 Nm @ 11.7 Psi / 0.82 Bar
3400 RPM — 379 Hp — 586 Lb-ft / 797 Nm @ 13.0 Psi / 0.91 Bar
3600 RPM — 423 Hp — 617 Lb-ft / 839 Nm @ 14.3 Psi / 1.00 Bar
3800 RPM — 466 Hp — 645 Lb-ft / 876 Nm @ 15.7 Psi / 1.10 Bar
4000 RPM — 511 Hp — 671 Lb-ft / 913 Nm @ 17.1 Psi / 1.20 Bar
4200 RPM — 548 Hp — 685 Lb-ft / 931 Nm @ 18.5 Psi / 1.29 Bar
4400 RPM — 588 Hp — 702 Lb-ft / 955 Nm @ 19.7 Psi / 1.38 Bar
4600 RPM — 621 Hp — 709 Lb-ft / 965 Nm @ 21.1 Psi / 1.48 Bar
4700 RPM — 639 Hp — 714 Lb-ft / 970 Nm @ 21.8 Psi / 1.53 Bar
4800 RPM — 656 Hp — 718 Lb-ft / 976 Nm @ 22.5 Psi / 1.58 Bar
4900 RPM — 666 Hp — 713 Lb-ft / 970 Nm @ 23.0 Psi / 1.61 Bar
5000 RPM — 675 Hp — 709 Lb-ft / 964 Nm @ 23.5 Psi / 1.65 Bar
5100 RPM — 682 Hp — 702 Lb-ft / 955 Nm @ 23.9 Psi / 1.67 Bar
5200 RPM — 683 Hp — 690 Lb-ft / 938 Nm @ 24.2 Psi / 1.69 Bar

Mean piston speed
The recommended maximum for routine service is 5000 RPM. At 5000 RPM the mean piston speed is 13.16 m/s (2590 ft/min). Reaching a commonly cited conservative reference of 15.24 m/s would require roughly 5800 RPM, which exceeds recommended limits.

Intercooler and charge cooling
The conversion specifies a liquid-to-air charge cooling (intercooler) architecture; documentation and supporting media describe charge cooling choices and installation considerations for reliable boosted operation.

Additional notes
The ASE-650 Saga maintains beneficial OEM BMW features where appropriate, while introducing aviation-specific modifications: dry-sump lubrication with external reservoir, piston cooling, even-fire ignition, and conservative operating envelopes favoring service life over high-rpm performance.

Technical specifications

• Engine type: 60° even-fire V12
• Engine code: M73-B54
• Cylinder block: AluSil with NicaSil coated cylinders
• Bore: 85 mm / 3.346 in
• Stroke: 79 mm / 3.11 in
• Displacement: 5379 cc / 330 cid
• Compression ratio: 8.0 : 1
• Cylinder bore centre distance: 91 mm
• Valvetrain: SOHC, chain driven
• Pistons: aluminium, custom CP with CT-3 hard graphite coating
• Connecting rods: Auto Verdi
• Connecting rod length: 135 mm
• Connecting rod / stroke ratio: 1.708
• Firing order: 1 - 7 - 5 - 11 - 3 - 9 - 6 - 12 - 2 - 8 - 4 - 10
• Oil capacity: 16 L / 4.25 US Gal
• Lubrication system: Auto Verdi dry sump system, external reservoir
• Idle speed: 1200 RPM
• Max take-off speed: 5000 RPM
• Mean piston speed at 5000 RPM: 13.16 m/s / 2590 ft/min