The Stowe design intends to create beneficial swirling turbulence in the combustion chamber? - WW in Virginia
Perhaps a bit of history can help everyone visualize what is taking place in the "Stowe" type 4 valve cylinder head.
If we jump back to the mid to late 1950's, racing engines of the period typically were 2 valve crossflow or hemi designs. The engineering dogfight was between the more efficient combustion of the wedge type crossflows, and the increased valve area available to the hemi design. Combustion analysis was just beginning to be understood. Engine engineers knew that the hemi, with its' poor combustion chamber shape, required higher total ignition timing to realize proper burn and develop the best bhp. The problem, then as now, is that high total ignition timing robs the working cylinder. It does this because the high initial timing requirement detracts from output when the piston/rod/crank assembly has to fight its' way to TDC, prior to performing any useful work. Engineers, designers and tuners of the period knew this and attempted to avoid this. The problem was that the prevalent thinking of the period, deemed turns in ports to be "bad" design, the "straight shot into the cylinder" theory, if you will. SO, for a "straight shot", valve included angles were very high. Some examples of this thinking: Jaguar hemis; Coventry Climax F1 hemis; Ferrari road & F1 hemis, etc. Port angles vary widely on these examples, but the BMEP's achieved were all similar @ around 185 psi.
When the first 4 valve Coventry Climax F1 engines appeared, they still used the high included angle, straight shot approach and the total timing required was still very high, limiting potential output. BMEP remained around 185 psi proving that combustion had not improved. BUT, these guys were not stupid, and they were aware that 2 valve OHV "wedge" engines could be built to achieve 185 psi BMEP, and they could achieve that figure with less total ignition timing, thereby inferring enhanced combustion efficiency. Combined with data from the SOHC 2 valve designers, where the valves needed to be offset from the centerline of the chamber, the supposed "ideal", these engine designs also required less total timing to achieve the same BMEP levels. This was where the idea that the inlet mixture "swirled" into the cylinder formed. It was idealized as a mini "tornado" of inlet gases, promoting homogeneous mixing of the air and fuel prior to the compression stroke. "Swirl" along with her brother "Squish" became the sought after components of efficient combustion.
And yet, the lure of increased valve area tempted the talented designers and engineers of the early 60's. Many designs were tried, many were less than stellar, but some showed promise. As the included valve angle went down, turns had to be incorporated into the inlet designs, but the specific outputs went up. It was Keith Duckworth who has to be considered the father of the modern 4 valve. His clever "pent-roof", center spark plug design was dismissed by the engineering giants of the time because it had no "swirl". And yet, it outproduced other designs, and achieved it with a low total ignition timing requirement, thereby proving efficiency. Duckworth theorized mixture motion into the cylinder as "barrel roll", a theory he did not share until years later. Afterward, "barrel roll" was labeled "tumble", and was thought to supplant, and be superior to: swirl. As we know now, there is a delicate "balancing act", between cylinder axis, valve angles (in both planes . . . ) and port axis angles.
As engineers and designers seek ever higher specific outputs from their "babies", all sorts of combustion aids have been, and are being tried. For 2 valve wedge racing engines (think NASCAR) "swirl" and "squish" were never abandoned. Some of the current combustion chamber designs go to great lengths to "centralize" the "swirl" and "squish" effects.
What Mr. Stowe has done with his unique 4 valve design, is to add a "swirl" component to the existing "tumble" mixture motion known to exist in 4 valve racing engines. I'm sure that most other designers considered his approach "over-complicated", in terms of efficiency payback. Only time will tell if the "payout" is worth the "complexity" for an OEM manufacturer. For individual hand built racing engines, I think he has proved his point.