Porsche, despite his withdrawal from WEC, has developed his 919 Hybrid focusing on maximising his performance in unique experiment to challenge laptime record at Spa.
This gave motorsport community the great opportunity to compare LMP1 and F1 performance.
Last occasion during 2017 Prologue in Monza has proven F1 to be faster, (1’30’’547 marked by Lapierre on Toyota TS050 vs. 1’21’’135 Hamilton pole position on Mercedes W07). But it is essential to remark that regulations changes during winter 2016 made F1 3-3,5 second faster and LMP1 nearly 4,5 second (at Le Mans) slower than previous racing season.
Porsche 919 Evo driven by Neel Jani marked an impressive 1’41’’770 at Spa Francorchamps (12” faster than LMP1 pole postion on 2017), but more importantly 0’’783 faster than F1 pole position.
To achieve such an impressive step several specifications of the car have been changed, without constrains given by WEC technical rules.
First of all no fuel consumption limit has been observed, causing a power increase up to 720 hp.
On hybrid side 919 Evo with his ERS system was able to reach 8,5 MJ per lap, way more than 6 MJ permitted by WEC for that car.
Weight saving on this prototype count a bit less than 40 kg removed from the WEC spec version.
Tyre compound used were softer and braking system benefit from fully drive by wire controlled on front and rear axle.
Most visible changes are surely on aerodynamic package that we will briefly review on this article.
Side view offer a perfect resume of developed aero package.
Starting from the front, the rounded shape of fender side profile is quite different comparing to the vertical leading edge used on WEC spec.
On WEC specification in fact, is common to use the vertical leading edge so to create a 3D effect promoting flow around the lateral surface of the fender rather than on top of it.
This creates more pressure on the fender nose, insisting on front splitter area and dive plates (creating downforce). This may create more drag but front downforce is essential for laptime performance.
Opposite design concept try to obtain more slender volume with curvy side view of the fender, reducing drag.
On 919 Evo front splitter has been developed increasing downforce leaving more space for efficiency improvements on car front.
Other distinctive features are the side skirt on bodywork between wheel arcs as well as larger end plates of rear wing and increased overhang.
Porsche 919 Evo (bottom) vs WEC spec - details of front fender, rear wing end plates and lateral skirts on bodywork sides
Rear wing is designed around 2 element airfoils with more camber and increased chord with respect to WEC configuration. Combining this with increased rear overhang and wider end plates enable a significant rear downforce improvement associated with better efficiency.
In nutshell wider end plates increase the effective wing aspect ratio (span/mean chord) that in turn means more downforce and less drag. End plates tend to limit the tip vortex generated by the pressure differences on top called pressure side (high pressure) vs the bottom side (suction side) of the wing, reducing the induced drag.
The wing positioned far back promote better interaction with the rear diffuser and more level arm effect on rear axle.
Porsche 919 Evo - details of rear wing with larger end plates and more overhang
Bodywork and underbody channel is responsible for a large portion of total downforce generation. In addition downforce obtained by car bottom is intrinsically efficient, with small impact on total drag.
Considering the effect on bottom surface flow due to developed front splitter, more extreme rear diffuser (discussed further) and his interaction with rear wing, the possibility to “seal” aerodynamically the side edge of the car, preventing an intense flow from top into the ground, is surely a great addition to generated downforce. This is obtained by well known “skirt” running alongside between wheel arcs.
This is obviously not permitted by WEC tech rules, but totally free on this Evo prototype.
Porsche 919 Evo – Side skirt along entire bodywork
Detailed view of more extreme rear diffuser design used on 919 Evo. Width is maintained but height is increased.
Moreover the centre triangular cone prescribed by WEC rules is totally removed obtaining an increased expansion ratio of the rear volume with larger downforce generation. Nolder on top and side tabs present increased dimension with consequent larger curvature effect on top and side flow, increasing air suction.
Porsche 919 Evo – Comparison of rear diffuser Evo (right) vs. WEC specification