Bob Lester at one time ran a Subaru engine before changing over to a Corvair. Problems with the crankshafts due to the high rpms necessary to produce enough power. Read the Auto Mathbook for some numbers of projected life expectancy when engines are subjected to higher and higher rpms. The Chevy 350 is 3.48 inches in stroke and will reach a piston speed that at 6500 rpms will stress the crank 4 times what it is at 5500 rpms per the author of the book. Yet by de-stroking that same engine as in the Indy cars, it can be revved to 11,500 and reach the same piston speeds as 6000 rpms, bringing the same stress to the crank. You must do the same things to your chosen engine, OR use an engine that develops more HP than you need, so that your rpms can be maintained at a reasonable level for longevity. The chosen engine needs to have a broad power band where torque is good where you plan to cruise. Peak Hp does not matter if you cannot stay there for long durations. Remember about takeoffs, climbs while in cruise flight. etc...
With the complexity with running a liquid cooled auto engine added to an already complex task of setting up an engine and then matching a prop to it, the idea of getting reliable information concerning PSRUs and prop matches is nothing short of daunting. The Subarus are reputed to produce X amount of HP but I was not impressed with their presentation nor information, or lack there of at Sun n Fun, from the Eggenfellner group. They seemed full of hipe but would not talk real world knowledge of their products. Like REAL hours of use instead of projected TBO. Their full rated HP falls WAY off when throttled back for economy cruise. For all the added extras in complexity and weight, you are better off with a good 2180 VW or Corvair 2.7L. The three best auto engines I have researched that are successful conversions, being used extensively, with LOTS of information available are: 1) the VW 2180; 2) the Corvair 2.7L ; 3) the 4.3V6 GM. By far these engines have way over the numbers of flying conversions that stay in the planes and the owners express satisfaction with their performance. The others have smaller numbers, and have short TBOs like the 2 cycle Rotax family. IMHO I would recommend for our birds, stick with the proven power plants and you will fly sooner, be happier, spend less money, and perform better than these other fancy boat anchors. (Ok maybe not boat anchor, but definitely tie down anchors ). Colin Rainey brokerpilot9...@earthlink.net EarthLink Revolves Around You.
