The 2017 Porsche 911 RSR, and How Its Mid-Engine Conversion is Legal

Arguably one of the news to come from the LA Auto Show was the 2017 Porsche 911 RSR, and more specifically, how the engine is in front of the rear axle as opposed to being behind it. Some accuse it of being a “waiver-mobile” like the GTE cars of old, saying that “it shouldn’t be legal; there’s no such thing as a mid-engined 911 that I can buy”. However, Porsche Motorsports Head Dr. Frank-Steffen Walliser has insisted that the new RSR is fully compliant with all GTE rules, and would require no waivers. After a brief glance of the LM GTE regulations, I can explain how, but first, I must make something clear. Technically, there is no such thing as a mid-engined vehicle.

So, paradigm shift aside, how can Porsche do this?The key to what allows Porsche to do this lies in Article 301 of the LM GTE regulations, which define the location, position, and orientation of the engine. The regulations quote.

Location : As original.

Position : Free.

Free, but the engine must remain longitudinal (or transverse) if originally longitudinal (or transverse).

So alright, the Porsche’s engine is still transverse, as on the road car. But how can position be free when the location must be original? How are the two terms even different? Well, lucky for you, Articles 035 and 036 of the LM GTE regulations have a definition for location and position respective.

Location: Defined relative to longitudinal centreline of the car, the middle of the wheelbase on the longitudinal centreline of the car, the engine compartment, the cockpit, the luggage compartment.

Position: Defined by dimensions (X, Y, Z) from the reference frame of the original car.

So, based on the definition of location given by Article 035, and the legal location given by Article 301, the engine must still be located fore or aft of the vertical plane representing the longitudinal center of the wheelbase, as it is on the road car. A simpler expression for this would be as per LM GTE regulations, only front-engined and rear-engined cars exist. Corvette and Aston Martin? Front-engined. Ford GT, Ferrari 488, Porsche 911? Rear-engined.

Now, with position being free within this rearward location, this allows the Porsche to move the engine forward. Much more forward. Forwards until the front of the engine meets either the longitudinal wheelbase centerline or the rear face of the rear bulkhead, whichever comes first.

Now, the Porsche isn’t the only car that takes Articles 035, 036, and 301 to their fullest. Pretty much every front engined LM GTE car, let alone most high-level GT cars have their engines moved back and down closer to the firewall with the conversion from wet-sump to dry-sump, and from a front transaxle to a rear transaxle transmission. In fact, I could be almost confident that every colloquial “mid-engined” GT car also has their engine relocated, although more subtly so. Porsche moving the engine so far forward, that it goes from being a colloquial “rear-engined” car to a colloquial “mid-engined” car is something that only Porsche, and cars like the Porsche could do.

So the for those who either decided to scroll down to the very end, or actually read this in full, let me present to you the shorthand explanation of how this is legal. Per the technical regulations, only front and rear-engined vehicles exist. The cars must still be front or rear-engined, and the engine must still be longitudinal or transverse, but from there, the engine can be wherever you please. The Porsche just uses these set of statements in an extremely clever way.

Don’t think this is so? How about you take a read of the 2016 LM GTE regulations yourself and see what you take from them.