Subaru debuts a turbo version of the FA20 engine

Yes, you read that right. But, before you get too excited, please note that it is not going under the hood of the Subaru BRZ nor any of its Toyota/Scion-badged siblings any time soon, if ever. Indeed, this groundbreaking piece of news was not obviously spelled out, but implied and buried in a superficially nondescript Subaru Global newsroom release on the Japanese iteration of the Legacy facelift that had its world debut at the 2012 New York Auto Show just over a month ago.

The title headline of that news release trumpets a 2.0 liter Direct Injection Turbo Boxer Engine. But which of Subaru’s two distinct new-school 2-liter flat fours is it based on? Is it the FA20 from the BRZ (1998cc, with 86mm bore and 86mm stroke) or the FB20 (1995cc, with 84mm bore and 90mm stroke) from the new 4th generation (GP/GJ) Impreza and 2011+ Japanese Domestic Market 3rd generation (SH) Forester? As Wikipedia reminds us, the FA shares little in common with the FB engine, with a different block, head, connecting rods, and pistons. In fact, one pundit claims that a few bolts are all the FA20 and FB20 have in common. While the aforementioned news release doesn’t specifically spell out which of the two the refreshed JDM Legacy and Outback will use, a comment that “the engine bore/stroke was made square (86mm x 86mm)” at the top of page 4 makes it crystal-clear that the FA20 is the first of the “F” series flat fours to be turbocharged. Yes, Subaru has yet to market a turbocharged version of the FB engine family (although it did show a turboed variant of the smallest FB – the 1.6-liter FB16 – at last year’s Tokyo Motor Show). What about the 2-liter turbo Subarus still available in Europe and Japan? Those are myriad variants of the older EJ20 family of flat fours.

The numbers
The Subaru Global news release is similarly semi-secretive when it comes to power output figures, with a small footnote mention of 221kW (300PS) power output and 400N･m (40.8kg･m) torque at 2000rpm. This translates to 296 hp and 295 lb/ft of torque, which boosts (pun half-intended) the FA20’s specific output from 100 hp/liter in naturally aspirated BRZ tune to 148 hp/liter.

The official Subaru Japan website and Wikipedia further reveal the use of a twin scroll turbo (for faster throttle response without giving up any top end), a 10.6:1 compression ratio (versus the naturally aspirated FA20’s 12.5:1), and word that maximum power output occurs at 5600 rpm, with maximum torque occuring between 2000-4800 rpm. Although not specifically mentioned in any text we’ve seen, expect Subaru’s signature top-mounted intercooler and a functional hood scoop. Most surprisingly, as the illustration above implies, an apparent 6000 rpm redline seriously alters the character of the FA20 from high-revving, low-to-medium torque naturally aspirated screamer to a much slower-spinning, yet far torquier engine. That, however, is just the beginning of the changes the FA20 has undergone on its road to turbodom.

Subaru DIT: a far cry from Toyota’s D4-S
The DIT acronym features prominently when describing the newest Subaru turbo powerplant, not only throughout the press release, but on a badge in the trunk lid and even atop the engine itself, as shown in the lower right photo. The initials, obviously enough, stand for Direct Injection Turbo. And that’s all the FA20 gets, not the Toyota-developed D4-S dual direct + port injection combo as applied to the naturally aspirated version of the FA20 engine. This is enormously significant, and has a number of repercussions. For one, it may be yet another tacit admission of the difficulty in boosting D4-S-endowed engines, an issue very familiar to tuners attempting to do so with the 2GR-FSE V6 and UR-FSE/UR-GSE V8s. Or is this simply another manifestation of Toyota’s own reluctance in allowing other companies to use their signature dual direct + port injection, as was the case with Lotus? The glass-half-full optimists, however (such as Car and Driver Backfires commentator Chris) will wonder if there will be people swapping the head from the FA20 turbo to remove the port injection on the BRZ/FRS/GT86 and make tuning easier and maybe get better flow through.

An unfortunate down side to many a direct injection-only engine, however, is carbon-clogged intake ports, a malady afflicting Volkswagen/Audi, Mazda, Hyundai and even Lexus’ direct injection-only 4GR-FSE V6 IS 250. Will Subaru’s FA20 DIT also be a victim of this? Not necessarily. For one, this is not a universal occurrence. As FT86Club.com member arghx7 reminds us:

People assume that just because VW and some other early adopters of mass production DI had valve deposit problems, they all must have valve deposit problems. There are a lot of different air/oil separator designs that have been introduced for use with direct injection over the past few years. Jaguar, for example, has a more sophisticated system to limit the amount of gas flow and oil sent back to the intake side under different conditions. Heated and cyclone-type crankcase ventilation systems also mitigate the problem. All these solutions cost money, though–development hours and higher part costs.

And Subaru, it seems, has expended the extra effort, for, as the always-knowledgeable NASIOC member Cocoa Beach Bum informs us:

(Subaru parent Fuji Heavy Industries) has submitted a US patent application which was published last month for “an engine breather apparatus that separates oil mist from blowby gas that is led from the crankcase toward the air intake system.” The original Japanese patent application was filed Sept 30, 2010, which was over a year and a half ago.

Or, as FT86Club.com member OrbitalEllipses so aptly put it:

A while ago, it was theorized on NASIOC that DI could be done without port injectors while still preventing carbon buildup on the valves through the use of a properly designed air/oil separator and valve timing. Voilà, a Subaru patent for what sounds like an air/oil separator!

A CVT transmission only?! What the…?!
In our recent Forester factor story, we lamented the loss of the enthusiast-oriented Legacy with the death for the 2013 model year of the 2.5GT turbo manual sedan in the U.S. Unfortunately, this is also happening, to some extent, in Japan. Sure, the Subaru Global news release mentions the 2.0GT DIT’s “SI-DRIVE” with Sport# (S#) mode allowing the driver to shift between 8 steps and an exclusively-tuned chassis with “reinforced suspension rigidity for better stability during high speed driving” and “vehicle sway (that) was minimized due to damper tuning and enlarged stabilizer diameter” for “superior stability when changing lanes and cornering”, not to mention standard “gun-metallic” 18-inch aluminum wheels and most enthusiast-oriented VTD (Variable Torque Distribution) all-wheel-drive system, but running this exemplary-seeming engine exclusively through a continuously-variable transmission?! Totally ridiculous, unless you’re one of the handful of CVT fans that are intrigued by the notion and engineering exercise of what is arguably the most powerful engine ever mated to such a Lineartronic (as Subaru calls it) transmission.

Beyond the Legacy 2.0GT DIT
Just take the little rant above as venting and fearing the worst, because, in reality, we’re quite pumped and optimistic about the potential for this new FA20 turbo engine. Perhaps Subaru is simply holding back for a few months or a year or so before we see a new iteration of the Legacy spec.B that combines the FA20 turbo with a proper 6-speed manual. And most pundits fully expect this engine to be the basis for the upcoming next-generation WRX and STI (possibly with yet another groundbreaking piece of new technology, an electric turbocharger). Why not use it to power a return of the cult-following Forester STI? Most of all, why not a proper, turboed BRZ STI?