Exhibition op limits have change considerably over last 10 years. For my C172 there is no geo radius for proficiency or maintenance flights after 40 hr phase 1 sign off. Passengers are allowed, as well as IFR. Again, similar limits to AB. JODA is correct regarding part 43 as it was previously certified airframe, so A&P required. In my case, I have a redundant Delphi EFI system (engine was designed for certification so it has a lot more features than needed for a home built) and other components of my making that no one else can really understand, so I asked for a waiver, technically approval of a maintenance program, allowing me to do engine work and condition inspection. Owner allowed maintenance is mostly required now, such as oil change every 150 hours (50 if I burn lead AVGAS) of Mobil 1 synthetic oil I get at local Walmart.

The most difficult part of conversion is initial paperwork. You need to demonstrate the modifications you made are safe, unlike a home built. This could require some level of documented analysis, such as a structural analysis by a DER or other qualified entity. Also, you may need to validate any new mods or parts that have or should have a time limited life, such as oil change intervals based on oil lab analysis history, or a component wear limits based on some acceptable means or by your testing using some acceptable basis. In my case, I also needed a pilots operating supplement and specific maintenance manual. The FAA or a DAR will take a good look during aircraft inspection at everything so be prepared for the unexpected as there is a lot of room for discretion on their part. Most of this stuff is out of the skill set of average builder so it can get expensive and likely not worth it for a one off. For me, I had the experience to put this together over time but still had months of back and forth with FSDO and MIDO. I would not recommend it, unless you can find the right MIDO DAR with experience in the EE category, or you buy a complete conversion kit that comes with the required docs.

again, not a path for most. For me it made sense, i fly the same c172 for about $18/hr that cost me over $60/hr with original O320, has push button start so no more hard starting issues, and it’s easier to fly for my kid without the mixture or carb heat, parts are about 60% cheaper, it’s quieter and more efficient, no lead emissions, and even out performs the newest c172. I just couldn’t rationalize or afford paying the $135/hr rental rate for a beat-up 30 year old 172 anymore.

FAA policy does allow for non-compensation flight training in EE as well. I’ve been asked to make the same c172 kit for others and put them in a flying club as current c172 rentals cost over $100/hr rental now....this would also be allowed as long as the club was a equity based club wherein members owned part of the plane. This likely wasn’t allowed 8 years ago.

the GM engine I use is a rated to over 500 HP (the redundant EFI system software restricts to 220 HP which was max certified for the 172), but I am planning on finding a faster experimental airframe to install another engine that I could use a 375 HP limit, which is a good power band for the engine...... A Year of initial engine selection testing I discovered running a V8 consistently more than about 65% it’s rated max considerably decreased reliability and engine life as aircraft and boat engines work exponentially harder than car engines connected to a transmission. If I use an experimental airframe which was never type certified, there would be none of the FAA or part 43 hassles or restrictions.....it would simply be a home built and I could have a repairmans certificate.

hope this helps update the topic.