Toroidal heads in Rc Model Boat engines.

Toridal heads are a proven performance mod in 2 stroke engines. The heads are much less prone to detonation than hemi style heads. They allow the squish to to be set the mechanical limits which give max compression.It has been reported by several modelers internationally and in the US that just bolting one on gave as much as a 1000 rpm increase. In an rc boat that could mean as much as a 3-5 increase in top speed mph.

Here what Jim Allen has to say about the heads hes tested in gas and nitro engines.

"I began steady state dyno testing of toroidal head shapes in 2010. Actual lake testing was also done with a Stalker Radar gun & A Commercial tiny tach mounted in the gas boats. Nitro boats used an audio tach mounted on shore.The information for using these types of chambers originated from other two stroke tuners who are using them on 50 to 400 cc engines; racing motor cycles; drag bikes; racing sleds; racing karts & very high performance two cycle engines.Some of the unique characteristics of the toroidal head design are as follows:1) There will be no detonation!2) At a 45 to 50% squish band area ratio, there will be a very high MSV. This is the result of closing the deck clearance down to it's mechanical limit. The mechanical limit is determined when the piston just begins to strike the head button in the engines over peak HP rev-range.3) There will be a very large increase in bottom end & mid range HP. One reason for this is because the toroidal head button's volume will be decreased by approximately 33%. The other reason has to do with the position of the spatking event, which is now centered in the chamber.4) Since the toroidal head has no detonation problems, the maximum usable compression ratio is determined by a drop in the HP at peak RPM.

I found in gas engines it was almost impossible to drive the engine into a state of detonation. The ground strap of the toroidal types is use for gas engines is approximately .016" away from the domed piston crown at TDC. There is no discoloration or indication of high heat under the piston crown with the deck clearance set at .002" to .003" in these engines. I can tell when the engine is over compressed only when the over-rev RPM's begin to sag off sharply. The head in the first photo is what I use for flat top pistons in the .90 cu in engine with 80% nitro, 12% ethylene oxide, 8% oil. Very easy to needle with no plug problems. The second photo is the gas engine head with a home made semi-surface discharge spark plug, which has the ground straps moved to the side of the center electrode. Notice how the ignition point is now centered down & positioned near the middle of the chamber in both designs. "

Jim Allen

#Heads