As I stated earlier, IF you are buying stunt engines, Then lapped AAC is the way to go, Lauri is an excellent machinist and has a huge base of help, if he needs it, But you cannot compare his engine to ones that you can buy, and Lauri is not going to sell you one, If a manufacture made what lauri is trying to compare engines to, they would want maybe 1000 a piece for them, It is a moot point anyway, It is not going to happen, '
The commercial available ABC AAC AAN ABN are excellent, I ran 1 PA in a Vectra for 9 years, 9 Nationals many team Trials and flew the plane all over the USA, massive range of condition, perfectly stable, Never a problem, and flew in contest many times with winds that were over 20 to 30 MPH. 3 of these were at Nationals.
If you have a ring in your engine, and is commercial built, it IS an inferior product.
The best way to make a ringed engine is to make it a double ring, with thinner rings, they conform to the distortion of a hot running engine better than a single thick ring, pin each ring 180 degrees from each other, and as Lauri has done make sure you use an aluminum piston and aluminum sleeve, Make sure you make it with a slight taper in the sleeve The AAC ring is the most stable you can make, The thermal expansion is the closest, Most of the problems with rings in St OS K&B FOX etc, were from steel sleeves, The expansion rates were much more different, even 2 identical ST 60 , 1 with steel sleeve 1 with chromed steel sleeve, the steel sleeve can run a tighter gap to start than the chromed one, even with extreme care taken on ringed engines, i have NEVER seen one go much past 500 flight without wear, degrading the performance, and I have rebuild thousands of these type stunt engines. NEVER have I seen a ringed engine go over 2000 flights with NO wear on the ring.
Lauri's engine is NOT , in any way, a typical stunt engine. It is a extreme example of 1 off custom built high tolerance engines. So if you are not able to do what he does, and are looking for available engines, there is ZERO reasons to compare the ones against his, the argument is pointless.
I have many custom made engines here, that have 100s of hours into them making parts and assemblies testing running, I have 8 ounce 64s, 7 ounce 40s, light extremely stable 55s, BUT these are NOT ones I could sell to people as a line of stunt engines at any reasonable price.
To close I will mention that there are STILL people flying engines from the 1980s and 90s that are AAC and ABC with great results, and they are still powerful stable and working perfectly, These include OS VF FSR , Clones, OPS rear Ex AAC, HP 40s, Royal 45s, PA 40s and 51s, OS 35 S engines, Thunder Tiger built Magnum AAC engines
Randy