The Bow-Tie Brigade

Many MiniCoupe builders successfully use the tried and true VW derived conversion for power.  That is the engine that Johnson envisioned; however, the design is robust enough that the smaller A65 and C85 Continentals have also been used with satisfactory results and Ron relates that up to an O200 is acceptable.  Needless to say these last are somewhat heavier engines, and in my case we’re going to trust the airframe with even more weight – that of a Chevrolet Corvair.  I find absolutely nothing inappropriate with the VW derived engines, it is just that I have a Corvair originally intended for a different airframe – so I’ll be adapting it for both budget and time reasons.

By now the Corvair, although nowhere near as accepted as the Volkswagen derived power plants, is not a mystery in homebuilders’ circles – with many KRs and Zenith CH600 series aircraft using this larger engine to good advantage.  The Achilles heel of the Corvair seems to be that at higher output, the crankshaft can become susceptible to vibrations and gyroscopic loadings that Chevrolet never envisioned, making the nitrated crankshaft a must for this conversion -- and increasingly the 5^th bearing (prop-hub) has become an implicit requirement for any of the higher-performance installations.

At least at the outset I’ll probably be using the trusty Keihin CV40 carburetor often used on Harley Davidson and Kawasaki motorcycles, among others.  The CV40 is a moderately altitude compensating carburetor – essentially akin to the CV Bings used by Rotax. – and again, it is what I have and am familiar with, so hope no additional investment will be required.  Further, I will be using the rare TRW forged pistons – in my case we purchased the 0.030 over-bored cylinders and pistons already painted and stored, awaiting eventual reassembly with the engine.

For the MutantCruiser, however, we will not be designing in as much Chevrolet power as is usually may be available from the Corvair.  Typical, for instance, the big 3100cc KR Corvair engines can churn out up to 135-140hp which is far in excess of what the MiniCoupe airframe can adequately use.  As I had planned in two early building attempts, my Corvair will be tuned closer to the level that Bernie Pietenpol used to good advantage in his admired AirCampers – about 85hp-88hp.  Although that is fairly small by Corvair standards, it is a nod to longevity and it is further envisioned that cruising output will be throttled back in the neighborhood of 55hp at a little less that 2700rpm, for a roughly 5-gallons an hour fuel burn. 

With reasonable consideration to aerodynamic cleanliness and a well-tuned engine, I am hopeful for a cruise in the neighborhood of 105-108mph which should offer sensible cruise fuel economy along with respectable power reserves for climb-out on hot summer afternoons -- of course faster would be better, but not at the expense of greater fuel burn.

We shall see…