RE: Norvel 074 vs Novel 061
Norvel made several .061 engines, but basically there were 2 revisions of 2 versions, if you follow.
Norvel made the Big Mig sport engines, with emphasis on easy running and the AME series, with emphasis on raw power. The Big Migs are much easier to run and idle better, in general.
In the beginning there were chromed cylinders with aluminum pistons. These cylinders have small finns cut into the cylinder mount holes, so that the fins are not full round circles, but have 4 flutes in them. These engines also typically have glued in carbs. They work well and are reliable.
Then, they developed what they called "revlite" engines, with ceramic coated cylinders (aluminum oxide, ie hard anodized). These have darker, dull cylinder fins, and the fins are larger than the chrome cylinder examples, fully enclosing the mounting screw holes. The carbs are bolted in. These represent the best of the Norvel engines (IMHO) and are longer lived and perhaps a touch more powerful than the older chrome cylinders.
About idle performance compared to the .074's. Not nearly as good, but still pretty good for 1/2 a once they're broken in and you've figured their nuances out. I'm flying a .061 on a Herr Aquastar flying boat. Running a 6x2 on Sig 25%+extra castor, it turns about 21,000 and is idling at about 7,000 rpm. That is slow enough to actually land the plane. Many here will report lower idles, but that's what I could get with the reliability I needed for a flying boat. I don't like recovery boats. I like to taxi back under power.
In about a dozen flights on her so far, no deadsticks.
J