- EPI Gen-2 Aircraft V8 Engine -
Performance, Features, Options
When the Gen-2 engine program began, the design was based on the same bottom-end technology as the Gen-1 engine (that is, improved SBC architecture), and the planned increase in performance resulted from a proprietary EPI cylinder head design and from several internal improvements.
The fact that the newer GM "LS" engine family incorporates most of the improved cylinder head technology which our proprietary SBC-style head design contained, combined with (a) improved engine block technology, available at much lower costs than custom components, and (b) the availability of high-quality LS aftermarket components, persuaded us switch the Gen-2 program to an LS-based engine. That allows us to further increase reliability, reduce weight and reduce cost.
The resulting Gen-2 engine is a normally-aspirated 441-cubic inch (7.3 L) engine based on LS architecture and built using the highest quality aftermarket and custom-designed components.
The following graph compares the expected performance of the EPI Gen-2 normally-aspirated 520-HP, 441-cubic inch (green) to the power and torque curves for the highly-optimized 500 HP 427-CI EPI Gen-1 engine (red) and the stock LS-7 (427-CI) engine (blue). The Gen-1 and Gen-2 curves illustrate the fact that with a well-optimized engine package, there is no point in using excessive crankshaft speeds.
As shown by the green curves above, the 520-HP (441-CI) EPI Gen-2 engine has been tailored specifically for aircraft applications. The LS cylinder head design has an excellent combustion chamber design, port configuration and symmetric port layout for good, even cooling. EPI has optimized the ports and valvetrain to produce a high but narrow torque peak in a good aircraft-engine operating range between 2670 and 3050 fpm mean piston speed (4000-4500 RPM).
The development of the Gen-2 engine was slowed by the fact that there was no intake manifold available for that engine family which is properly configured to produce the high, narrow torque curve of the Gen-1 engine. Therefore, we designed an LS-architecture intake manifold which enables the engine to produce optimized power and torque curves like the Gen-1 engine.
Because the operating range of the engine is limited by design to 4500 RPM, the valvetrain loads can be reduced considerably, leading to improved engine life expectation. Since the acceleration loads on cam followers increase with the square of RPM (with respect to the same cam profile and valvetrain components), the needle bearings in the roller cam followers are notorious for failing under sustained high speed operation. Our tailored valvetrain has modest cam-lobe acceleration values, lighter spring loads, and components designed to move their resonant frequencies as far away as possible from strong excitation frequencies and harmonics.
The Gen-2 powerplant (no longer available because of our current focus on new, "clean-sheet" engine designs) was available in both normally-aspirated and turbocharged form, and incorporated the following features:
- Improvements to the engine block to enhance stiffness and reliability.
- Improvements to the crankshaft to enhance torsional vibration characteristics and fatigue life.
- Improvements to the connecting rods, wrist-pins and pistons to further enhance component life and wear characteristics.
- New cylinder head technology with improved combustion chamber configuration, optimized port shape and cross section, improvements in heat rejection, octane tolerance, airflow rate and airflow quality.
- An integrated accessory drive with:
(a) redundant drives for the high-efficiency Coolant Pump,
(b) dual 80-amp alternators,
(c) (optional) air-conditioning compressor,
(d) (optional) AND-20003 pad (for a mechanical fuel injection pump) and
(e) (optional) AND-20000 pads (for vacuum or hydraulic pumps).
- A new wet-sump oil system which provides the same windage reduction as our previous dry-sump system, but removes about 30 pounds and considerable complexity from the installed configuration, and reduces the cost by several thousand dollars;
- The option of:
(a) an electronic injection / ignition system, optimized for aircraft performance requirements, with redundant FADECs and critical sensors,
(b) a conventional aircraft (Bendix-type) mechanically controlled fuel injection with improved nozzle technology, providing improved vaporization, low SMD particle size and the resulting improved combustion properties.
- Two completely independent, low drain ignition systems with one coil-per-cylinder which provide reliability comparable to dual spark plug implementations.
- The turbocharged version used a High capacity, density controlled turbocharger with intercooler, having sufficient capacity for sea-level power to at least FL230 and pressurization to higher levels;
- A new PSRU (the Mark-15) which contains improved vibration, bearing, and reliability technology that evolved from the successful Mark-9 PSRU (described as "bulletproof" by several of its users). The Mark-15 supports reversible propellers, which can provide substantial reductions in landing distance. It can be configured to turn the propeller in either the same direction as the engine or the opposite direction to the engine, enabling twin-engine configurations having counter-rotating propellers, with both engines turning in the same direction. Counter-rotating props can provide significant improvements in engine-out controllability and reductions in Vmc for twin-engine aircraft.
The installed weight of a powerplant is a critical consideration. The weight analysis of the Gen-2 powerplant, based on existing components, indicates a complete firewall-forward installation package (including: powerplant, accessories, FAR-23-compliant engine-mount structure, 125 pound Hartzell™ certified propeller, turbocharger, wastegate and controller, intercooler, coolant and oil heat exchangers, cowl, plumbing, and fasteners) would weigh in the neighborhood of 915 pounds. A normally-aspirated installation with a 75-pound propeller can be expected to weigh approximately 125 to 150 pounds less.
For purposes of weight comparison, the complete firewall-forward installation of the Continental GTSIO-520-F on the Aero-Commander 685 (engine mount, complete engine, Hartzell ™ prop, turbo, cowl, oil, plumbing, heat exchanger, fasteners) weighs about 930 pounds.
Two EPI Gen-2 (turbocharged) powerplants installed in place of the GTSIO-520's would decrease the empty weight of the aircraft by 30 pounds. That represents a slight increase in payload (an additional 5 gallons of fuel). It also increases the installed power from 750-870 to 1000 HP.
By way of further comparison, the complete installation weight for the Orenda V8 Installation in the Aero-Commander 685 (powerplant and accessories, engine-mount structure, 125 pound Hartzell™ prop, turbocharger, wastegate and controller, intercooler, coolant and oil, heat exchangers, cowl, plumbing, and fasteners) was over 1260 pounds.