According to the document posted at Miata.net (registration required to see the image), Mazda will alter camshaft lift and valve size on both the intake and exhaust side, fit freer-flowing exhaust, and smooth and enlarge the piping on the air intake side. There are also internal engine modifications: lighter pistons with lower crowns for better swirl in the combustion chamber, lighter connecting rods, and a crankshaft balanced for higher-RPM operation. All those extra revs mean extra vibration and noise, so Mazda will ditch the single-mass flywheel for a "low-inertia" dual-mass flywheel – which will attempt to find a nice balance between DMF damping action and SMF directness. Overall, it's a pretty serious engine revision with some driveline changes that will heavily affect the driving characteristics of a fantastic driver's car.
Contributing Editor James Riswick and Senior Editor Alex Kierstein, both well versed in Miatas past and present, are here to analyze what this could mean for the little roadster.
James Riswick: I don't know much about them lighter crank combustion rods, but I for one welcome the news of more power to the Miata. The jump from 155 to 181 seems like a very prudent Mazda-like thing to do, accomplishing that task through various aforementioned technical wizardry as opposed to slapping on a turbocharger, exclaiming "yee-hah" and calling it a day.
Alex Kierstein: That's true. I'm wary of additional power, but you do make a good point that at least this is the right way to do it. Going all-motor will keep the bright responsiveness of the engine intact. But higher revs might make power delivery peakier. Frankly, I'd be ok with moving the torque and horsepower peaks up a bit in the rev range, making it a bit more work to access the engine's sweet spot. The dual-mass flywheel should also help if low-end torque suffers, so less stalling in traffic.
JR: Did wonders in the 911 and 718s.
AK: And, as you were saying to me earlier, no turbocharger plumbing means less additional weight. How's it compare to the Mazdaspeed version of yore?
JR: Well, let's go to Screen #1! Mazdaspeed Miata of Yore produced 178 horsepower and 166 pound-feet of torque, and weighed 2,529 pounds. The 2019 will produce 181 hp and 151 lb-ft of torque. Mazda's listed curb weight for the 2018 is 2,332 lbs. I figured that would be for the lightest Sport model, but Car and Driver weighed a loaded Club at 2,309 pounds.
Either way, it really is impressive how the new Miata weighs 200 pounds LESS than a predecessor from 15 years ago ... er, yore.
For the record, the current 155-hp Miata Club went from zero to 60 mph in 5.9 seconds. That Mazdaspeed Miata did it in 6.7 seconds. (Both numbers from C/D as they have them both published online, and presumably would've used comparable methodologies, if not timing technologies)
AK: All right, it's time for me to play the role of Miata fundamentalist channeling James May here: aren't you worried this will ruin some of what makes the ND Miata so wonderful? It's already an easier machine to carry speed with, less of a momentum car even than its portly NC predecessor. I fully recognize I'm a small, unusual subset of Miata lover, but I worry that it'll lose some of its fundamental charm. Although anything that would induce me to rev higher and row gears more would be welcome ... and more revs and a higher power peak would do that.
JR: What you describe is a Honda S2000, and I didn't particularly like that very much. It needed a 7th or 8th gear on the highway. "I'm going 70 why are you at, like, 4,000 rpm!?!"
No, I do not think it's a problem. I have a lot of faith in Mazda's engineers and the brand itself. I don't think they'd muck up their pride and joy. Especially since I can't imagine there's much marketing pressure on the Miata at all. They aren't getting calls to bump things up because the new Pontiac Solstice has this much more horsepower, and the Toyota MR2 Spyder has this much more, and the Mercury Capri ... you get the idea. They're all dead.
AK: Good riddance. Except for the MR2. And without real competition, as you point out, this strikes me as part of the battle plan all along. A power bump keeps things fresh a few years into the ND's lifecycle. We have to be nearing the point at which everyone who wants a 155-hp Miata has one ... perhaps a 181-hp version will get some folks off the fence. I suppose I'll be cautiously optimistic that it'll be a more thrilling car, even with a surfeit of power. But on the other hand, I don't think this genie goes back in the bottle. By cranking up the output, Mazda sets this expectation that the specs matter more than the experience, and at each iteration it'll look odd if the numbers don't climb.
Are you worried about that, at all?
JR: If it keeps going up and up and up, sure, then they would lose the script on the Miata. Yet, history would indicate that's unlikely. The base Miata upon which the Mazdaspeed Yore Edition was based, had 142 hp. The ND's 155 hp was actually DOWN from the NC.
Let me also say that the Mazdaspeed Miata was an absolute hoot to drive. As timing and luck would have it, I got to drive one when I was just starting out as an intern, and I definitely enjoyed it more than my father's NB. Using that as reference, I can say I would happily take a more powerful Miata every time.
Of course, I'm sitting a floor above a Z3 with 189 hp that weighed 580(!) pounds more than today's Miata, so I'm certainly not a Miata fundamentalist despite being around them since the very beginning.
AK: Likewise, even though I'd get another 1.8-liter NA in a heartbeat. Perhaps the most fun I've ever had in a Miata was a LS-powered Flyin' Miata NC named "Atomic Betty", so who am I to judge? In any event, we're all excited to find out how more power will change the character of the 2019 Miata. Based on the evidence we've seen, this power bump seems to be happening, and it'll be fascinating to see how it plays out both on the road an in the court of public opinion.