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Enough information is coming in on the new 9A2 turbo engine fitted to the 991.2 911S to compare it to the outgoing 9A1 and previous Porsche engines. The picture that emerges is of a relatively conservative effort that was likely less expensive to develop and produce, but that doesn't technically push the envelope.
The 9A2 is clearly a close derivative of the modular 9A1 family that powers the current 981s and 991s. Visually it appears to share most components and castings, with the turbo plumbing bolted on after the fact, adding 77 total pounds. Lighter engine components, particularly the exhaust, offset some of this weight, bringing total weight gain to 44 lbs.
Stroke is down slightly, from 77.5 to 76.4mm. This last number is interesting: it's the same stroke that was used from the 964 through the 997 GT3/ RS, but it's no longer seen in the lineup.
Bore is down to 91 mm from 102 mm, while the cylinders are now iron lined. The resulting 2.981 liter displacement suggests Porsche has no intention of racing this engine: engines that race have round numbers to maximize displacement (3.800 liters for the old Carrera S, 3.600 for the 76.4 mm x 100 mm Mezgers, etc).
While power and torque are both up 20 hp and 44 ft/lbs, respectively, weight is up even more. This is the other indication that there are no racing aspirations: compared to the outgoing 3.8S in 400 hp trim, power per pound is down over 6%, while torque per pound essentially equal. The previous engine wasn't a standout in either respect, and the new engine is now slightly below competitive engines like the M3/ M4 in terms of power to weight. Porsche is clearly capable of making far lighter, more powerful engines- the GT3 makes 25% more horsepower per pound, the 918 makes double the power for its weight. This translates to between 80 and 200 extra pounds hanging behind the 991.2's rear axle vs Porsche's more upscale engine technology making the same power.
The upside here is that the engine itself is over-designed and likely to be durable, as is normal for any of the lower end of the 9A1 family. I expect main bearings, block bottom end, etc to be shared with the Turbo S (as is current practice from the Boxster up). It seems likely that both a 991.2 GTS and next generation engines will make more power with minimal changes. Even so, it looks certain that beyond peak power and efficiency the forced induction 9A2 will fall short of the 9A1 in most areas of engine performance.
The 991.2 is faster than the 991.1, but technically the engines seem to have moved the game backwards in many ways- more complexity, more weight, little upside other efficiency. Apparently Porsche felt comfortable enough with the 991's competitive position to save money in this area.
This is all fairly normal practice for Porsche and shouldn't come as a surpise: the 981s are also carrying around 100+ lbs they don't need due to overbuilt engines, but it does lend perspective. Porsche saved money on the engine, though this does let them put the cash to work elsewhere in the chassis to maintain overall value.
Comparison images of the 9A1 vs 9A2, and an exploded view showing the 9A1's modularity:
Thanks for posting this. But I am curious to learn why calling this engine has no "racing aspiration" by purely basing it on the displacement and weight. Racing engines have significantly different criteria to meet, as in rebuildability and having specs that fit within the guidelines of whatever series it is raced in, than mass produced street engines, which is always about efficiency, long term durability, and cost effectiveness. By definition, and with the departure of non-DI mezger engines from few years ago, non of the current Porsche engine has any racing aspiration either, including the current GT3.
The overall power and tq delivery of 9A2 is both significantly stronger than 9A1, not just the peak figures, which the post seems to ignored while other members have clearly illustrate such in another thread. It just seems a little biased to call the entire engine a step back just because it's weight and displacement figures. True durability and performance of this engines will only be found when this engines are starting to be tuned and tracked hard. I would reserve my judgment on these engines until we have all the information on them, like how much of the internals (crank, con rod, piston) are forged to handle the added stress of forced induction, are bearing designs adequate this time, and types of turbocharger used in 9A2, etc. Passing off speculation as information is just not exactly informative, do you not agree?
I thought about this after I posted before, and I think this is a pretty interesting and important discussion for Porsche lovers of recent generations. It would be interesting Pete to see how these engines compare design wise to the M96/97 and of course to the all hailed Mezger block.
Jim
Great post - I love this type of technical analysis. It's amazing how many magazines/reviews skip over this stuff to regurgitate Posche press releases. Thanks.
I would say the the new engine is designed for/takes the 911 even further down the GT cruiser track. It prioritizes low-rpm torque over high end power and responsiveness. This is what most GT buyers like on the street.
Think about it - this engine is another piece of the puzzle bringing the 991 closer to a MB SL class two door - smooth ride, automatic transmissions, power when you want it like a light switch, don't have to think/work to drive it. Opposite of a purist/enthusiast type car. Not that low-down torque isn't enjoyable to drive on the street.
Maybe it's so close to the 9A1 to enable it to live on in the GTS in NA form without excessive cost.
Do you think the new PSE centered exhausts have something to do with trying to make it sound better as opposed to aesthetics? Coming straight out the back of the muffler?
New PSE
Regular Exhaust
Current 991.2 PSE on an S. Notice two center mufflers.
Petevb, Do you think the new PSE centered exhausts have something to do with trying to make it sound better as opposed to aesthetics? Coming straight out the back of the muffler? New PSE Regular Exhaust Current 991.2 PSE on an S. Notice two center mufflers.
09-12-2015, 12:44 AM
991.2 9A2 engine vs 9A1 technical analysis
