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35 q Clearly visible are the twin counter- rotating crankshafts at the base of the Gurney MC4S motor. The crankshafts for this twin-cylinder engine are about half the length of an inline engine's, and they sit in a one-piece cast aluminum sump. The head and sump are held to the block via seven through bolts. T h e h e a d a n d s u m p a r e h e l d t o t h e b l o c k v i a s e v e n t h r o u g h b o l t s . p In addition to a dramatic reduction in vibration and elimination of the engine's fore-aft moment, the MC4S also features an optimized four-valve head design that improves airfow and power output to turbo engine levels on pump gas. to 5.0 in. (38-127 mm) are mentioned with an oversquare range of 1.1 to 4.5 possible. The squish area for the fat-top pistons ranges from 24% to 35%, with a preferred area of 31.5%. With this squish area, the preferred mean piston speed is less than 4,200 feet per minute. By examining more than 200 valve confgurations, Gurney and his team discovered that small changes in the intake and exhaust angles had huge efects on output. Specifcally, a 15% increase in the cubic feet per minute delivered high velocities: 0.5 to 0.95 Mach. (Most naturally aspirated engines have a velocity below 0.4 Mach.) Each pair of intake valves has a combined area (in square inches) of 28% to 38% of the bore, while the same measurement for the exhaust valves is 14% to 20%. In addition, the intake ports have a combined area of 42% to 65% of the valve area, with 53.4% seen as ideal. Intake ports are set at 7.9° to the left of vertical, while exhaust ports are angled 8.4° to the right of vertical. Three intake and exhaust port designs were created for the MC4S: straight, improved and optimized. Both the improved and optimized designs fowed more air, but the optimized design showed signifcantly more area in terms of fow versus valve lift, and a consistently greater volume than the straight confguration. The improved port confguration is an intermediate step, with a Venturi shape to the intake port and a gradual curve to the exhaust port. However, it is the way in which the features of each are interconnected that produced the experimental results Gurney and his team hope to replicate in the metal before the end of 2015. Critical to the design of the intake ports is the shape of the inside radii, which forms a Venturi that allows the fow boundary layer to follow the shape of the port, and reduce pressure in the pipe in order to increase fow. Almost as critical to fow are the valve seat and valve seat undercut angles. For the optimized design, the preferred intake valve seat angle is between 48° and 52° with a valve seat undercut of 38° to 42°. For the exhaust valves, these numbers are 40° to 52° and 45° to 65°. Compression ratios from 9:1 to 10.5:1 were investigated with the optimized porting system, and simulations showed a BMEP (brake mean efective pressure) more than 100% greater than found on most naturally aspirated engines. It also showed that the efect of increasing the compression ratio leveled of, leading to the conclusion that the MC4S engine can produce high power outputs with a lower compression ratio. This reduces stress on the engine, and results in a power loss of less than 2.0%, according to the simulations. These also show that a 1.8-liter four valve with straight porting should produce 141 hp at 8,000 rpm when running a 9.5:1 compression ratio. Moving up to the optimized porting increases this number by 85%, giving a theoretical power output of 262 hp on pump gas. Like his friends and colleagues say, Gurney is on to something, and it doesn't need turbos. With its transverse counter-rotating crankshafts and perpendicular camshafts, intake and exhaust, the MC4S would appear to be well suited for installation in a motorcycle. The rigid sandwiched block construction, compact integrated gearbox, rotational moment cancellation, signifcantly reduced vibration, and porting along the bike's axis mean it should package well and eliminate many of the problems that plague current larger displacement inline or V-twin engines. In addition, it would make an ultra-low vibration/high efciency engine for a range extender EV. It would be relatively easy to adapt the MC4S to a transverse front-drive "end-on" gearbox or a rear-drive transmission. It might even be advantageous for reasons of cost, vibration, rigidity and crashworthiness to keep the perpendicular twin cylinder head design, and replicate it for any additional pairs of cylinders. (A mode canceling eight cylinder would be amazing with an intake-exhaust/exhaust-intake/intake- exhaust/exhaust-intake head layout and turbine-like smoothness.) Then again, mating an optimized port twin cylinder design with a 48V electrical system might be all that's needed to produce a powerful, quiet and smooth hybrid powertrain. The possibilities, like Dan Gurney's fertile imagination, are endless.