http://www.roarracing.com/?p=1814
ROAR proposes specifications for 1:8 competition 4-stroke engines
To encourage the development of new technology for 1:8 nitro racing, ROAR is establishing guidelines for four-stroke engines that, if produced, will be permitted to run alongside the current two-stroke engines at any ROAR National Championship or sanctioned event.
Four stroke engines have dominated the SX world, and they’ve eclipsed the performance of the two-stroke engines once thought to be superior in terms of total power and power-to-weight ratio. The proposed specifications are taken directly from the displacement increases permitted in SX racing, and the bore and stroke dimensions are in direct proportion to the engines powering modern SX racing machines. As is often the case, technology and specifications that are ideal in bigger engines don’t always translate to the engines used in RC racing, but as a starting point, these will be the recommended specifications. ROAR encourages any engine manufacturer to confidentially discuss these specifications with ROAR prior to construction using a different specification.
Converted four-stroke airplane engines have been tried at random points in our past, but these engines were never configured for high power output, or for the rigors of RC car racing – they were simply airplane engines adapted to fit RC cars. But proper four-stroke technology applied to RC car engines can offer increased efficiency, a reduction in exhaust noise, and as seen in the SX world, potentially much more usable power.
Due to the higher number of moving parts, the costs of a four stroke engine can be greater, so economy in the design is paramount. There are some allowances in the proposed specifications that could mean additional costs. These are all open to discussion and perhaps the specifications can be more narrow if it’s proven that a simple and less costly technology can produce similar results to those that are more costly.
Proposed specifications:
Bore: 23.15mm
Stroke: 14.96mm
Displacement: 6.30cc (.384 c.i.)
Single cylinder only
2 to 4 valve configuration
Must use a single camshaft
Pushrod or OHC permitted
Spark or glow ignition
Air cooled only
Additional specifications will develop if and when engine manufacturers decide to produce such an engine, but these basic specs are sufficient to begin the discussion.