Why Porsche considers this the third generation of this engine architecture
Porsche is kissing its 991-generation 911 goodbye with a series of 1,948 very special cars, and we can now reveal more about what’s under the hood. The wraps were pulled off two new 911 GT3–based Speedster models—the first to be prepared by Porsche’s GT-car department—at the 2019 New York auto show. One was a $275,750 USD “base” model in Guards Red; the other was a Heritage Edition version resplendent in GT Silver and decorated with $24,510 USD worth of additional vintage racing graphics, badging, and a two-tone black and cognac interior.
Recently, we spent some quality time with the engineers and learned quite a bit more about the powertrain motivating these special cars. It is indeed GT3-based, but this was no mere engine swap. In fact there is so much new engineering involved that Porsche considers it the third generation of this engine architecture.
The three main engineering revisions are for compliance with stricter European emissions regulations—particularly the particulate standards. To prevent these dangerous particles from forming in the first place, you want the fuel spray droplets to be extraordinarily fine. Toward this end, new injectors operate at higher pressure (3,626 psi versus 2,901) and spray a different pattern of fuel into air that enters via individual throttle bodies. (These are also credited with improving throttle response.)
Exhaust now exits the engine through a new super-thin-wall exhaust system that integrates the forward silencers. Particulate filters live in a cylindrical housing that is brazed using an innovative nickel-steel solder capable of withstanding the intense heat of an exhaust system. This saves a few precious grams over the welding process that Porsche formerly used to fabricate the exhaust. In all, the system weighs 22 pounds (10 kg) less than its predecessor, and pounds shaved off the very back of a rear-mounted engine bring compounded benefits in terms of weight distributions and polar moment of inertia. Note that in place of the particulate filters, U.S.-bound cars will get an inert substrate that simulates the filters’ back pressure.
9 Horses & 7 Pound-Feet
These changes boost output to 502 hp at 8,400 rpm and 346 lb-ft of torque at 6,250 rpm. The 2018 GT3 engine produced 493 hp at 8,250 rpm and 339 lb-ft at 6,000 rpm. Note that the second-gen GT3 engine’s metric horsepower rating of 500 was previously reported as 500 SAE hp, but the real improvement is 9 hp.
As in the last-gen GT3 4.0-liter, the valves operate without hydraulic lash adjusters, yet the factory-set shim valve adjustment is expected to last the life of the engine, so there are no access plates to service them.
More Speed with Fewer “Speeds”
911s have featured a choice of seven-speed manual or dual-clutch PDK transmissions for quite some time now (and these very different transmissions share internal ratios), but manual GT3s and this new Speedster make do with six ratios. How do they compare? The gear ratio spread is one-third narrower, with sixth gear penciling out 14.3 percent shorter. EPA ratings suffer without a super-luggy top gear (who cares!?), but this setup allows the Speedster to reach its 192-mph (309-km/h) top speed in top gear (at about 8,150 rpm).
Strong Launch, Great Pull
First gear is also shorter (by a scant 0.4 percent), which allows for righteous hole shots. (The clutch is reinforced to withstand this.) Working up through the gears, you’ll enjoy a shorter-throw shifter and that the spacing between the ratios is 18 percent closer on average. Working back down through the gears, you may enjoy the Auto Blip rev-matching function (and if not, this feature now gets its own button, which leaves all blipping to your heel and toe).
By removing a pendulum mass damper from the flywheel (whatever vibes it would have attenuated will likely be appreciated in this application) and getting by with one less ratio, the six-speed weighs in a full 37.4 pounds (17 kg) lighter than a seven-speed PDK and 8.8 pounds (4 kg) lighter than the seven-speed stick.