As I returned it became apparent that there were some fellows who would "hop up", "modify", "fix", their own engines and there were others who did this for a price to others

    And it is one of the sadder aspects of modern stunt. For the most part, with a few exceptions, the results are disappointing.

    It started in earnest in the late 70's when people were trying to make various RC schneurle engine work for stunt. The reason was that these engine, when they worked, provided astronomically better performance. Unfortunately the techniques of the day were not up to the tasks, and the result was extreme detuning until they worked no better than the existing engines (ST46 and later 60). The necessary breakthrough was discovery of the use of a tuned pipe as a regulator instead of a power booster, in about 1986, and since about 1988, modified schneurle engines with tuned pipe have utterly and completely dominated the event in the US. It's simple, it's well-understood with volumes of precise information on exactly how to make it work, and is a solved problem. The result is that far more people than ever have managed to become competitive because getting an adequate engine run, time after time, is a turn-key system.

     The single best stunt engine ever produced by a major manufacturer, regardless of era, is a bone-stock OS-40VF with a pipe. Period. If someone tells you otherwise, they don't know what they are talking about.

   Unfortunately, again, this development was missed or intentionally fought, and people are *still* detuning engines to run on a muffler with a 4-2 break at low revs. A few people do it reliably with good craftsmanship and repeatability, and although it provides a tremendously less effective system than a conventional piped system, it will work as well as it did in 1975.

   While the techniques to accomplish this are now well-known, this has encouraged a vast army of amateur engine experts who will do this for people, variously referred to as the "Head Gasket Patrol", "Hack patrol", "local engine experts", etc. Typically, the goal appears to make an otherwise good engine (like the 46LA) into the most gutless 4-2 break engine that technology will permit.

   In the regular competition world, the discontinuation of the 40/46VF, OPS 40SPA, and other early tuned pipe engines, other semi-custom manufacturers arose. Randy Smith was the first, collaborating with Henry Nelson of T/R fame. These are another cut above the consumer OS 40VF and others, with more flexibility and even more durable, and as the size went from 40 to 51 to 61 to 75 (after the FAI permitted them) much more effective power, permitting a very flexible system that you can make run the way you want. This was followed by the RO-Jett, manufactured largely by Nelson competitor Dub Jett and developed by Richard Oliver. This one provided the sort of run of a 40/46VF with much more effective power.

    There were other purported "revolutions" along the way, but most of them were either backwards steps (modified ST60s running like 1975 again) or no net improvement (4-strokes, which run well if you run them exactly the way they have to be run, but have nearly zero flexibility) and ST60 tribute engines with 20 years of sensible development (Discovery Retro and similar).

  There are also various small RC engines like the 25LA and similar, that are much superior substitutes for old "35-sized" airplanes. The Head Gasket Patrol exists largely to try to lower the performance of various schneurle 40s (40FP) to what is required by old Fox 35-sized airplane (like the Twister, etc). The correct solution is a dead-stock engine that is about half the size, and leave it alone.

    Brett