You have probably heard two criticisms of the Miata—if you’ve been looking into things closely—that make sense. One is that the steering is like the electric steering from the RX-8. This is probably because it essentially is the electric steering from the RX-8. The other is that, despite all of the compressions, the two beautifully-lightweight engine options don’t want to rev. The source of this is the SkyActiv-G motor that you have heard about in the ads; the formula is basically to throw a long stroke and small bore together for efficiency, then make up for this with amazingly high compression so that the car will get into triple digit horsepower figures even in its weaker forms. Unfortunately, not even most SkyActiv 1.5s top 99 SAE at the flywheel; very high compression, for all of its goodness, can only just barely make an undersquare 1.5 in a 2016 Miata/MX-5/Roadster top the 1.6 from the same car in 1989.
The gift that keeps on revving.
Granted, the engine I’m referring to is the B6ZE: an engine only made its maximum 120hp in JDM Roadsters, and was also undersquare. But it was less undersquare, and even still is subject to limited criticism for not befitting the Miata’s driver’s car nature as a less-than-rev-ecstatic engine. Its successor, the 1.8 BP, was nearly square and scrutinized less so. Fortunately, the SkyActiv line comes in various geometries, meaning that the charm and excitement of S2k’s pretty crazy (and over 9,000) FF20C can still be brought to the Miata without prohibitive development costs for Mazda. The Miata is certainly light enough to make a peaky screamer of an inline four work, so why not give it an engine that can spin high enough to deliver yet more (I’m cringing too) smiles per gallon. My facial muscles had a hernia.
Well, if you made it past or skipped the sales pitch, here’s how Mazda can use its parts bin to make an oversquare-engined Miata that neatly retains the current model’s displacement of 2 liters. By using the crankshaft, rods, and related components from the Mazda 2’s 1.3 along with the block from the SkyActiv 2.5, a displacement of 2.041 liters and comfortably oversquare bore/stroke combination of 89:82mm would be achieved. Along with some better-flowing heads, intake manifold with shorter runners, and hotter cams, it could transform a new Miata model into a formidable track tool. Moreover, the second generation of SkyActiv engines will boast 18:1 compression, or a 5 point increase over the current two liter. Marginal compression would likely be sacrificed for airflow, but the combination would still be potent. Combining these two factors properly would require quite a few supporting modifications, but could be worthwhile for the raw agressiveness and high output that such an engine could demonstrate. It would make sense to keep the torque-oriented motor in the current model aboard, but such a “hybrid” powerplant could prove to complete a pure and focused sports car Miata variant to satiate the crazy few. The daytime running catfish and Leapfrog on the dashboard would be A-okay with me.
tl;dr 89mm bore, 82 mm stroke, 4 cylinders, 2 cams, 16 valves, 18:1 compression in a 2,300lb car with a 1:1 sixth gear.
Images courtesy of MazdaRoadster and R&T.