. . . the engine—the 2018 M5 uses the same basic powerplant as the 560-hp 2011–2017 M5, mildly updated. It is now a 600 hp, twin-turbo, 4.4-liter V-8 known within BMW as the S63B44T4. S is the typical designator for production M engines (ordinary BMW motors use the prefixes N, M, or B). The second number is displacement—the M5’s engine is 4.4 liters. The T bit represents a technical update—this is the fourth major update the S63 has received since the design was launched, in the 2010 X5 M and X6 M. (The changes for the ’18 M5 are in detail: new turbochargers with larger compressors, a new oil pump, and so on.)
The S63 is a neat mill. Its layout is colloquially referred to as “hot vee”—the engine’s exhaust manifolds rest inside the vee made by the the cylinder heads and block, as opposed to outside it. The engine's intakes live on the side of each head—the place where a traditional vee engine puts its exhaust. This sort of setup is occasionally referred to as “reverse flow,” because it mirrors how the majority of vee engines, automotive or not, have operated for the past century. BMW chose it to maximize responsiveness; the layout allows for a clever (and patented) exhaust manifold that would be practically impossible in a cold-vee setup. Along with a nontraditional firing order, the arrangement allows the engine’s turbochargers to be fed exhaust pulses at even intervals. Which results in more linear power delivery—and less turbo lag.
Short version, made palatable for people who aren’t tech doofuses: The S63 is built in a cool, nontraditional way, chasing linear response, a BMW hallmark.
Like its predecessor—like every S63—the new M5’s engine produces torque everywhere. Virtually any point on the tach, in buckets, great flowing gobs of the stuff. It is a firehose of violence. In terms of power delivery and character, it is one of the great modern engines, a shocking combination of linear thrust and willingness to rev. There is lag, but it is so minimal that you barely notice.
. . .
. . . power isn’t that much different—the F90’s 600 hp was essentially matched by the 600 hp in the F10 Limited Edition—but its delivery seems to have been massaged to be smoother . . .