MAR 2015

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

Issue link: https://experimenter.epubxp.com/i/471466

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Page 30 of 36

EAA Experimenter 31 Recently, Higgs and businessman Kevin Eldredge (builder/owner/pilot of the Reno Super Sport racer Re- lentless) formed ACE to improve Lycoming 360 and 540 engines. What is left of the originals are the engine crank- case and accessory cases, plus a few wear parts—bearings, gears, washers, gaskets, etc. Major new-design parts include cylinders, cylinder head covers, valves and springs, pistons and pins, con- necting rods, crankshaft, camshaft, sump, plenum, and induction tubes. The valves are solid, with small stems to reduce mass, lowering stresses on cam lobes, reducing wear, and allow- ing a lower spring rate in the single valve spring. Guides are aluminum-copper. Higgs said, "Heat absorbed by the valve during operation is approximately 70 percent via conduction through the valve head, so we use a seat mate- rial that releases this heat more effectively." The monolithic cylinder, with its removable hard- coated inner aluminum sleeve, eliminates the problem of cracked head/cylinder joints. Its heavy fins (with more surface area than the standard part) have a wavy shape and are spaced for maximum heat transfer. They're made of a 354 alloy (rather than traditional 242) for increased thermal margin, and they are attached to the case with spherical washers, reducing stress in the flange area—an expensive and effective practice usually reserved for radial engines. The completely new design of the combustion cham- ber allows the use of very low octane nonaviation fuels. (100LL is rare in many parts of the world.) The ACE design is compatible with all ethanol and methanol fuel types—E10, E15, E85, etc. Note to legacy engine owners: the ACE cylinder is a drop-in replacement for most 360/540/720 engines; a bonus is its bosses for knock sensors and direct injec- tion. (AC cylinders will become individually available as production of new engines allows and will require AX pistons and rods. And the AX50 pistons require oil squirt jets.) HOW DIFFERENT ARE THE MA JOR COMPONENTS? The slipper-skirt pistons differ from legacy parts to keep inertia low; the 5.125-inch part weighs just 823 grams (versus 1,360 grams for the Lycoming part). As an engine runs, each piston stops twice per revolution, facing thou- sands of g's and transmitting incredible loads to the small end of the rod. Lighter pistons help bearing and moving parts a lot. For reference, the standard 360 piston has an inertial force of about 1,358 pounds versus 821 pounds for the AX50 piston. At top dead center (TDC), the piston reverses; the standard part's inertia is 1,798 pounds versus 1,072 pounds. Heat helps pistons fail. Ironically, so does a thick pis- ton crown, as it absorbs and holds heat, even as it tries to This photo of a piston from a test engine clearly shows the large amount of swirl in the ACE combustion chamber. The 409's 4-bolt big-end connecting rod shows how little clearance is available between the crankshaft and the camshaft on the big stroker engine.

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