Menestrel HN700


A suitable engine was found in Switzerland and it came out of 1994 Subary 1800. The engine type is Subaru EA81, normally aspirated, single carb. There is a lot's of data on the web about the use of this engine as an airplane powerplant, so the following information will focus only on our specific points.  The plan was to use a reduction drive, but as the Menestrel has a tiny firewall the resulting cowling would have looked funny. Results from c.g. calculations promoted further the use of a direct drive only.


The engine was disassembled and re-balanced: crank (with prop hub and new flywheel), the rods and the pistons. The engine housing was shot peened with glass beads. A thread for a "jesus bolt" to secure the flywheel to the end of the crank was drilled and tapped and the bellhousing remachined. Oil drain fittings from the turbo were drilled and tapped  next to the oil pump above the oil level. The cam was re-profiled.

Cylinder heads

The intake of the single carb heads is really restricting and needed some attention. A specialist in this field was engaged and Tipi did the porting of the heads.

Prop hub and flywheel

The prop hub and flywheel were designed by ourselves and the parts were machined from 6082 aluminium by Jukka Kallio.  The starter ring gear was heat shrinked onto the flywheel and it came from an old Saab. After some research it was noted,  that all european cars use the same tooth shape for the starter, which enables one to mix the parts fairly nicely. Subaru uses strange 9 mm bolts to attach the flywheel and the flywheel was designed to accommodate the orginal bolts. The prop hub is bolted to the new flywheel. The propeller flange is based on the SAE2 specs.

Engine mount and attachment points

Attaching the engine to the mount can be a really tricky task and there are a lot of solutions  how to do it. In the end we bought the engine mounts from Stratus Inc. The pattern of the Stratus mounts is similar to the Limbach attachments, so the concept of the Menestrel engine mount could be re-used and just needed to be re-calculated againts JAR requirements. The upper points of the Stratus mount are fastened by the cylinder head stud bolts, which are a little short for this task. Stratus recommended screwing them out a couple of turns  from the block and attaching them in position with thread fastener. 


The turbo used is an IHI RHB52 with Subaru EA82 specs. It has a water cooled centerpiece and an integrated wastegate. This turbo has a common known problem with cracking the wastegate housing, which was encountered in the build as well in a second hand turbo. A lot of energy was spent to find another brand because of this weakness and high cost of a new unit, however carbon seals are available only for the IHI. Eventually we purhcased a a new unit and used only the intake housing from the old initial turbo.

Water: The cooling water to the turbo comes from a water draining plug found underneath the left cylinder head and it returns from the turbo to the water expansion chamber just before a thermostat.

Oil: Our engine block had an oil pressure gauge and this port was used to steal the oil to the turbo. A T-fitting for the gauge was manufactured and it was connected inline to the hose between the engine and turbo. The return oil is routed to a fitting machined to the engine block next to the oil pump above the sump oil level.

The position of the turbo is behind the engine and the height is roughly the same as the engine block upper corner. There is only 20 cm between engine and firewall (because of c.g.), so the space is very limited. 

Exhaust pipe

Stainless steel pipe was sourced from various places, however it was next to impossible to find 40 mm tube with a thin wall thickness. Rauno Pylväläinen produced some  by pressing half a donut to a flat plate and then welding those two donuts  together. The flanges for the exhaust ports and turbo were water-jet cut from a thick stainless steel plate. The exhaust pipe connects together just below the turbo and does not have any flexible joints. The turbo/carb package is suspended from the upper engine mounts with flexible rubber mounts. Carb and cabin heating was difficult, as the exhaust pipe doesn't have a single straight tube.  There is  now a rather small box with for the carb heat and cabin heating.  The inside of the cowling is really warm and there have been no icing tendencies with the Zenith-Stromberg 175 CD Carburetor so far in this set-up.


The cylinder head intake port has also a water port underneath the intake flange, resulting in a fairly complicated intake design. Subaru has originally water circulating underneath the inteake manifold to avoid icing. The intake needs to clear the starter, alternator and not to be too high. It was manufactured out of aluminium and turned out really nice - we used the original Subaru intake flanges cut out from the intake and machined flat.