Many of us that consider building our own airplane hear about why we should not even think about using an auto engine in our project. It’s about the same argument as “if man were supposed to fly, he’d have been given wings”. I began by examining what was available in the certified market. It left me with a feeling that there was a lot to be desired. These engines were designed in the 1930’s and have remained relatively unchanged. Not many positives by the standards of a modern engine. Big cubic inches, low horse power, inefficient. I began with of my understanding of the auto engine from 15 years of experience in drag racing. My first choice was a Mazda 13B rotary engine. Fewer moving parts, low weight, just not very complicated. But in order to get the horse power I wanted there would have to be many internal modifications to get the engine flight ready. I also looked at many other combinations, but I couldn’t seem to find one that didn’t have me making some sort of compromise. I met Bud Warren at my first Copper State Flyin in 2006. His display interested me because of his PSRU he had on display. This was something I was going to need no matter what engine I decided to go with. He told about the GM Ecotec line of engines and in particular the LSJ motor with the supercharger. This combination had 205 Hp and 200 Ft Lbs of torque. There will always be some modifications to an engine, but there are no internal mods necessary with this line. Also, they ranged in horse power from 142 to 260. The cost of a crate engine (these are very complete crate engines) is from just under $2k to just over $4K for an LSJ motor. The Ecotec was available in a variety of GM products such as the Cobalt, Saturn, Saab, and the HHR to name just a few. The LSJ motors were in the Cobalt SS and the Saturn Redline.The LSJ engine or the similar turbocharged version will weigh 314 lbs. Firewall forward package should come in right at the same weight as an IO-360 certified engine or about 425 lbs. The motor is an all aluminum engine with a seven quart oil pan, forged crank, rods, and pistons. The advantage of a forged crank in an auto conversion is that they are designed to have a certain amount of flexibility and are less prone to cracking or breaking. A cast crank is rigid and that could be a problem. When you’re swinging a prop and shut the engine off, that’s a great deal of inertia to stop. No matter what PSRU interface you are using (with the exception of the Bud Warren designed centrifugal clutch), a certain amount of that energy has to be absorbed by the crank. The supercharger has a built in intercooler. To get more boost at the rpm range for flight, you can change the front pulley on the supercharger to a smaller diameter unit. On the turbocharged unit just adjust the waste gate. I have checked with people in the know and they have indicated that stock injectors and fuel rails should be sufficient at those lower rpm ranges. The engine will never see over 5000 rpm. Each project has its’ own set of requirements and engine selection should be based on those requirements. A firewall forward option will cost less than a similar certified package. I am going to go the other route by acquiring my engine through an outside source, build my own motor mount, an adaptor to interface my PSRU to the engine and all of the associated pieces for this build.The first order of business will be to create a cradle to support the engine. The cradle will be attached to a mockup of the firewall so as to get the proper reference attach points based on the prop shaft centerline and the cowell positioning. This will reduce the costs of this conversion even more. This total should be between $15k and $20 for a firewall forward build. A running total of the costs will be posted as I go. To date, I have spent about $3800 for the engine and the associated components and $2100 for my PSRU. I am lucky that I found an engine with 391 actual miles on it; (kid 0, curve 1) . The cradle is based on a small furniture dolly. This dolly is rated at 300 lbs. I reinforced it with the angle iron and two additional wheels. You will notice that I bolted everything together rather than welding. Eventually the engine will come off the jig. Welding will leave a very large unmanageable chunk of metal. The engine is totally square in the jig. Angle iron works well for this purpose. It’s strong and inexpensive. It doesn’t look pretty, but it is pretty stout. Also this is something anyone can build who doesn’t have welding skills. Having it on wheels means it can be moved around if necessary. It can be separated from the firewall when needed. The plywood represents the firewall. There is a small circle located toward the center that was transferred from the firewall blue print. This is the prop shaft centerline. The jig was built to locate the engine on this centerline with the use of a lazar mounted on a tripod. The supercharger is the reason I chose this engine for my project. The pulley on the snout of the supercharger will be changed to a smaller diameter one to provide more boost in the rpm range that engine will operate in for airplane use. This tangle of hoses and wire harness is what you are going to start with. This will eventually be replaced by a new harness and stainless steel hoses. Click any of the attached pictures below to get an enlarged view.