991.1 GT3 engines Everything you need to know about Porsche’s GT-spec MA1 flat six

The 991.1 GT3 is a brilliant sports car when on song, but is its engine its weak point? Total 911 investigates… Written by Kieron Fennelly

991.1 GT3 engines - Why were they recalled, and why have they been revised? Our deep-dive reveals all

The BURNING QUESTION of the 991.1 GT3

Schadenfreude – pleasure at the misfortune of others. Strangely, this human if rather reprehensible trait has no word to describe it in English and the language has to resort to a foreign word to convey the sense. And that human trait was evident in February 2014 when reports appeared of engine fires in Porsche’s latest flagship, the 991 GT3, released only the previous autumn. Plastered across social media and on the inside pages of what we used to call the popular press was a picture of a brand-new 911, a GT3 no less, blazing itself to destruction. For several days, the newsfeeds poked fun in that slightly sneering way that they seem to reserve for Porsche drivers. But this tabloid entertainment hid a serious problem which would rumble on inside Weissach for several years.

“Only Porsche is still building a pure, naturally aspirated engine, unencumbered by air or mechanical supercharging”

In the aftermath of the headlines, Porsche reacted with alacrity: all owners of the new GT3 were told to stop driving them and to contact their supplying OPC which would collect the car. It was anticipated that repairs – a new, revised engine – could take several months, and owners received compensation which included a loan 911 for the duration. In all, 785 cars were recalled, an exercise estimated variously to have cost Porsche a good 20,000,000 Euros, and owners informed that they would receive new (modified) engines. The contrast with the way the company had reacted to 996 and Boxster owners, whose engines had been destroyed by a disintegrating IMS, was striking. But then, the circumstances were different: the 991 GT3 failures all occurred within weeks of delivery. IMS failures happened largely outside Porsche’s two-year warranty – which meant that the company was relieved of any strictly legal responsibility. The absence of social media two decades ago meant owners were left seething on forums, but could do little else when Porsche merely offered a replacement engine at an alleged 40 per cent discount. Porsche had reckoned correctly that outside the realm of pure enthusiasts, its reputation would not be materially affected.

There was no such cynicism in 2014: the company needed to forestall more bad publicity (which, by reacting quickly, it managed fairly successfully) but there was also the question of what went wrong. There was considerable disquiet in Weissach that the bespoke 3.8, a significant rework of the stock 3.8 unit of the 991 Carrera S, of which Andreas Preuninger’s men were understandably proud, was apparently faulty. Recalling all the engines enabled the motorsport engineers to analyse the entire production and discern whether this was the endemic flaw they feared it could be. Within a matter of weeks they would conclude it was.

The 991 GT3 was the first entirely new GT3 since the original 996 in 1999. The larger 991 platform allowed huge technical advances in terms of electronic chassis control, notably re-steer, and for good measure it also featured a new engine. The beloved ‘Mezger’, which in its final production guise had produced 500PS for the 4.0 997 RS, was consigned to the history books; a more modern design (which incidentally did not require its own separate production line) was developed. The 9A1-M used the crankcase, timing chains, cylinder head bolts (and ancillaries) of the Carrera S 3.8, but the head, pistons, connecting rods (in titanium), competition valve gear and a pure (i.e. separate) dry sump were all specific. Even the crankcase was reworked with more oil jets and hollowed for the higher compression pistons. This engine was designed to produce its 475 PS maximum at 8,250rpm yet rev to a dizzying 9,000rpm limit. Amongst series production engines only Honda’s (much smaller) four-cylinder VTec unit reached these altitudes.

“We always want to stretch to the limit,” said Preuninger at the launch of the new GT3 in 2013. “High rpm is an emotion for me and it is a unique selling point for our cars. It’s fun, sounds great and it’s also efficient: you produce power by revving higher. You just have to construct the engine in such a way that it can live with the revs for 100,000 miles.” The correspondents were deeply impressed: the direct-injection 3.8 of the latest GT3 was smoother, sharper and even more ballistic than the 3.8 Mezger, they found. The absence of a manual gearbox option was the only significant adverse comment, but the honeymoon was not to last long.

Within a few weeks after the recall, Porsche admitted that the fault had been traced to the fixing of the connecting rod to the crank. The rod had come loose and in the case of the fires, had gone through the block, a common enough occurrence with highly stressed racing engines. Leaking oil had then ignited. The attachment of the rod to the crank was blamed and it was widely speculated, though Porsche did not confirm this, that an air tool used to set the torque had somehow lost its fine calibration; the rod screws had a very narrow torque tolerance and the incorrect tightening force could subsequently allow the rod to work loose and finally detach itself. An article in Excellence magazine offered this perspective of the mechanical forces involved here: “This engine has a 9,000rpm redline at which speed the crankshaft revolves at 150 times/second, each piston comes to a complete stop 300 times/second and at maximum rpm, reciprocating weights could exceed 20,000kg.” The article went on to point out, quite rightly, that this is a phenomenal set of figures for a road car intended to be driven daily.

Porsche announced further that it was working with its supplier to revise the fastening of the rod to the crank. It gave no more detail than that. This revision process was not rapid and it was a good four months after the recall before new engines, listed internally as E1, were ready. These were sent out to dealers to fit in customer cars which had been sitting engineless since February. That might have been the end of the story and indeed for most GT3 customers it was, but it might appear that the narrative of the 9A1-M saga would continue. Some enthusiasts even wondered what else Porsche had decided to modify during those four months, which seemed a long time to design and test a new connecting rod fastening. What is significant is that the launch of the 991 GT3 RS was delayed nine months, until Geneva 2015. The RS had a four-litre flat six, but it was vastly more than a simple boring out of the GT3’s 3.8: with specific camshafts, connecting rods, pistons and its own crankcase made from the same exotic alloys as the 919 race car, this was clearly a different engine. This time Preuninger said that increasing capacity (rather than the rev range) was the route to more power and interestingly the rev limit was set at 8,800rpm rather than the 9,000rpm of the GT3.

Meanwhile if the revision of the connecting rod fastener seemed to have done the job, there were still mutterings about the durability of the 3.8 of the GT3. Of all the 911 ‘clans’, GT3 owners, especially track day devotees, are by far the most vocal if they perceive even the slightest power deficit in their steeds and there was talk of high-speed misfires on some cars. On one hand this might be dismissed, as can many of the claims made by individuals on the internet, and the occasionally wild exaggeration of IMS and later bore-scoring dangers is a case in point. However, it was clear that Weissach was not satisfied either, for between 2014 and 2016, no fewer than three versions of the 3.8 were built. The E1 was the replacement after the recall, F followed in 2015 and G in 2016 incorporated many of the cylinder head revisions of the 991 RS four-litre unit.

Porsche was particularly sensitive to ripples emanating in North America, by some distance the largest GT3 market, and by 2017 one association of GT3 lobbyists calling themselves the concerned owners’ group (COG) had evidently caused enough of a stir for Porsche to go into action: in August 2017 Weissach boss Frank-Steffen Walliser flew to the US and met this group at the company’s headquarters in Atlanta. His candour evidently impressed the assembled owners, for he began by announcing a much improved ten-year/120,000-mile warranty for all the GT3 991.1 cars (see boxout above) and then went on to present a model of the camshaft with finger followers. An intermittent flaw in the finish on some followers was said to be responsible for the high rev misfire which had provoked a steady series of complaints.

In an explanation which had sufficient technical detail to make those present feel their concerns had been taken seriously, he indicated exactly what, Porsche believed, was causing this high-speed misfire which affected only a minority of GT3s and the steps Weissach had taken to resolve it. As a damage limitation exercise Walliser’s was a five-star performance: technically the solution appeared convincing, was well presented, and the special warranty took all parties by surprise.

Of course, among GT3 owners, grumbles went on and they always will, because the car represents a level of driving perfection simply not to be found among other marques, though complaints about the current-generation GT3 did fade. Perhaps the affair also helped to put into perspective what is now a unique powertrain. Only Porsche is still building a pure, naturally aspirated engine, unencumbered by air or mechanical supercharging whose steroidal, but artificial effect cannot but create a distance between driver and machine. Always naturally aspirated, the ‘Mezger’ GT3s began with 100PS per litre and finished with the 125PS litre of the 997 4.0 RS; on subsequent GT3 generations Porsche has continued to make a production engine which despite ever greater environmental strangulation, still offers an output of 125PS/litre.

As Excellence observed, this is effectively a racing engine certified by its maker for road use. Seeing as significant further development of production petrol engines is unlikely given political pressures, the 9A1-M series fitted to the Porsche GT3s must undoubtedly rank as the greatest naturally aspirated engine ever made. Porsche’s efforts to produce such an engineering feat is remarkable, and its resolve in giving an unprecedented warranty is admirable.

BELOW Porsche’s brilliant 991.1 GT3 is a big rework from the 997.2

Porsche’s 911 991.1 GT3 extended engine warranty

“Porsche will extend the warranty on the engine of all 991.1 generation GT3 vehicles in all markets with respect to failure modes related to this issue. The extension will provide coverage for ten years from the original in-service date, or 120,000 total vehicle miles, whichever occurs first (the base bumper-to-bumper warranty remains unchanged at four years or 50,000 miles for the US, as do all other warranty terms and conditions). The warranty extension is fully transferable to any future owner. All US owners will be informed in writing and the change will be applied and processed with no additional owner action required. If a vehicle shows the described failure patterns (e.g. misfire at high revs and check engine light) and the inspection in the workshop shows the failure patterns, Porsche will replace the defective engine with a new engine having the latest parts. Porsche confirms the issue is isolated to the 991.1 GT3, and that the 991.1 GT3 RS and the 991 R are not affected.”

ABOVE The 991.1 GT3 was PDK only, a decision Porsche reversed for subsequent GT3 models