The New Porsche 911 RSR Features Its Largest Flat-Six Yet

This is the discussion thread for a recent post on GTPlanet:

This article was published by Kyle Patrick (@SlipZtrEm) on July 8th, 2019 in the Automotive News category.

 

W... why u no 992...?

 

4194cc? Drop a 4.3L Vortec V6 in that bad boy and make some serious horsepower.

 

nice car

 

I wonder if there will be a flat eight in the future, because this car is basically a prototype.

 

I'm surprised this is still based on the 991.2 platform. Maybe not all that surprising, but still.

 

It would be cool if Porsche put a flat eight in the 911, though the normally aspirated flat sixes they use in the GT3 and the RSR are mighty impressive engines. At the very least Ruf has put V8s in 911s.

 

Porsche does have a history of using flat eights, I would fully support them if they would use them again (not they they would be interested )

 

I wonder how much displacement they can keep adding before the returns start getting marginal.

 

They'll need to add some more cylinders eventually.

 

Love these mid engined RSRs, sacrilege though they may or may not technically be. I'm not exactly a Porsche fan, barring a few individual models, but this one ticks the boxes alright.

The exhaust note has lost a little now the exits are so wide apart on the car, and the obvious use of a (relatively long) balance pipe doesn't help. Still, it's great to still be hearing proper NA machines such as this, even though they're ridiculously inefficient compared to a turbo, never mind electric or hybrid.

In essence, I think they may turn out to be peak Porsche for many years to come.

They were particularly troublesome for Porsche, and nonetheless among my favourite engines ever made. Their stillborn 16 cylinder is also up there, and suffered similar issues for the same reasons. Both engines basically re-trod the path of inertial woe that BRM's H16 was faced with.

I honestly doubt they'll revisit those exact configurations. Something about the 180° "V" angle doesn't play nicely with the required 90° intervals in the eight and, in the two different types Porsche investigated, either the crank twists itself apart or the engine has terrible balance. The exhaust packaging was a nightmare, too.

I still reckon they could have another crack at a third or fourth configuration, just for me.

 

I'm going to miss the scream of the current one. Watching them in person at the Petit Le Mans at Road Atlanta has been fantastic. This year's race is going to be very sad with the screaming Porsche RSR's last race and the Ford GT's last race,

 

Thanks for this! I didn’t explore the history of those flat-8s, didn’t know that they had issues.

I guess I hope that at one point they can't just increase the displacement without increasing the cylinder count while sticking with the naturally aspirated engines and they'll introduce the flat-8 again. Given how much technology has evolved, I could see them being quite successful.

One can always dream

 

A Boxer-Eight (B8) sounds very interesting but I don't see it happening because of the emission regulations in Europe.

 

Out of curiosity, I looked into it again a bit more...

Spoiler: off-topic lecture

That flat-eight Wikipedia article in particular has expanded with more examples. The aero engines (Lycoming IO-720 and Jabiru 5100) are boxers with a firing order that indeed implies a third type of crankshaft (as opposed to the two tried by Porsche). Because they're still in use / production, the datasheets / manuals are freely available.
I'd somewhat ignorantly say the Jabiru is a more recent "copy" of the stalwart Lycoming; firing order for both is 1-5-8-3-2-6-7-4.

Given the aero usage, I would imagine the torsion problems associated with the "twin boxer 4" setup that Porsche tried is less of an issue with this "third" configuration. Either that or the low rpm helps. But then the aero types are not small engines, which compounds the source of the torsion: the pistons' inertia. Propellers are not known to tolerate torsional vibration; the Lycoming at least has "dynamic" pendulum / bob-weights on its crank (tuned mass dampers), which would also eventually make an appearance in BRM's H16...

What I find interesting is the timing of all of this. The Lycoming first flew in 1961. The Type 753 in Porsche's 787 / 804 project was started in '61. BRM's ill-fated H16 was '65 into '66, dead by the end of '67, in part thanks to persistent crank failures; Coventry Climax's flat-16 (FWMW) was shelved before the end of '65 after less than a year of development, due to catastrophic crank torsion issues.

Porsche's high-specific-performance, 3-litre version of their boxer-eight (simply Type 908) was '68, and it suffered crankshaft related issues in both configurations; the flat-sixteen was '68 / '69 also. Even though the smaller displacement boxer-eight engines were reliable enough, they always seemed to make less power than anticipated, as though power were being "sapped" somewhere - torsional vibration is known to do this.

This seems to show how Porsche, at the time, twice failed to learn the lessons / follow the example set by others. Or at least it shows an ignorance of the torsion issues that the aviation industry had no choice but to pay special attention to in the '30s / '40s. Bearing in mind there's no straight-forward analytical solution to the piston inertia problem, it can only really be "solved" numerically and by trial and error - which meant lots of tedious, iterative hand calculations for anyone without access to a "computer".

Maybe Porsche would only entertain an eight cylinder boxer again as a sort of last hurrah or homage or race only project etc. They would have to think very carefully about why it didn't work previously and fully explore the possibility space, analysing the situations with the engines from other manufacturers as well. I have no doubt they can make it work armed with today's computer-aided analysis / design approach.

I look forward to it immensely