Gt3 RS Hp/ Displacement liter
02-19-2018, 05:32 AM
#1
Burning Brakes
Thread Starter
Gt3 RS Hp/ Displacement liter
I believe that the highest hp per liter achieved by ferrari in a NA engine was 4.5 * 135 = 605 for the speciale.
I believe porsche engineers are just as able to push the limits but on their peak NA car they have now done 4.0 * 130 = 520.
So they've left 20 hp on the table. Are they planning a special end of run beefier RS for 500 VIPs?
Or are they just playing it safe with the engine to avoid problems of pushing the envelope too far?
Perhaps porsche numbers are conservative and power is closer to 540? While ferrari's numbers are actual (not conservative).
How much of a factor is flat 6 vs V8 in this difference? I suspect not much or porsche would not have done even 130/liter, just 5 shy of the speciale's 135/liter.
I ask coz this gen 2 needed to hit 540-550 (even after exiting the hp wars) with the norm among other brands increasingly 700+ (be it with turbos).
You can only do so much on the turns, ultimately on track days non-professional drivers are only allowed to overtake on the straights so hp is very handy and needed.
I believe porsche engineers are just as able to push the limits but on their peak NA car they have now done 4.0 * 130 = 520.
So they've left 20 hp on the table. Are they planning a special end of run beefier RS for 500 VIPs?
Or are they just playing it safe with the engine to avoid problems of pushing the envelope too far?
Perhaps porsche numbers are conservative and power is closer to 540? While ferrari's numbers are actual (not conservative).
How much of a factor is flat 6 vs V8 in this difference? I suspect not much or porsche would not have done even 130/liter, just 5 shy of the speciale's 135/liter.
I ask coz this gen 2 needed to hit 540-550 (even after exiting the hp wars) with the norm among other brands increasingly 700+ (be it with turbos).
You can only do so much on the turns, ultimately on track days non-professional drivers are only allowed to overtake on the straights so hp is very handy and needed.
02-19-2018, 10:27 AM
#2
You may well be correct that Porsche has left something on the table at 520 hp- I’d also guessed slightly more. However hitting 135 hp/ liter with a 4.0l 6 is significantly more technically challenging than with a 4.5l 8, so the result is perhaps not entirely surprising. The Ferrari’s advantage is largely down to the geometry of its smaller cylinders and in particular how this relates to airflow.
Power comes down to the ability to breath at high RPM, and breathing is limited by the valves. Both engines squeeze the largest valves possible into their oversquare bores, but because the Ferrari has more, smaller cylinders it also gets also gets more, smaller valves. That doesn’t initially seem advantageous as more, smaller valves leaves the resulting valve area unchanged. However consider that at lower valve openings air must flow through the small gap around the perimeter of the valves, and it’s there that smaller cylinders have a big advantage.
The net is that the Ferrari’s V8 has roughly 12% more valve perimeter for its displacement. That lets it breath better and make power more easily, much like the engine in Porsche’s own 918 Spyder. This advantage can be seen even more clearly as cylinders get smaller still, where 200 hp per liter is achievable on modern super bikes like the bmw s1000rr using tiny .25 liter per cylinder displacements to simultaneously breath better and rev higher. Given that small cylinders are the key to making high specific output Porsche’s 130 hp/l from .67 liter cylinders is impressive compared to Ferrari’s 135 hp/l from .56 liters/ cylinder. For comparison the Atom V8 achieves its stratospheric 167 hp/l largely due to its tiny .375 liter cylinders (closing on half the size of the Porsche’s).
Bottom line I would not assume that headroom has been left for a future version at this time. I don’t see any real ability to increase revs, friction has largely already been removed to the extent possible and breathing must already be close to the limit. Simultaneously the shadow of tightening emissions regulations looms large. I’m sure more power is available with more substantial changes (I’m betting on a cam change and little else for the RS), but it seems possible that time’s run out for those revisions before the curtain comes down.
Power comes down to the ability to breath at high RPM, and breathing is limited by the valves. Both engines squeeze the largest valves possible into their oversquare bores, but because the Ferrari has more, smaller cylinders it also gets also gets more, smaller valves. That doesn’t initially seem advantageous as more, smaller valves leaves the resulting valve area unchanged. However consider that at lower valve openings air must flow through the small gap around the perimeter of the valves, and it’s there that smaller cylinders have a big advantage.
The net is that the Ferrari’s V8 has roughly 12% more valve perimeter for its displacement. That lets it breath better and make power more easily, much like the engine in Porsche’s own 918 Spyder. This advantage can be seen even more clearly as cylinders get smaller still, where 200 hp per liter is achievable on modern super bikes like the bmw s1000rr using tiny .25 liter per cylinder displacements to simultaneously breath better and rev higher. Given that small cylinders are the key to making high specific output Porsche’s 130 hp/l from .67 liter cylinders is impressive compared to Ferrari’s 135 hp/l from .56 liters/ cylinder. For comparison the Atom V8 achieves its stratospheric 167 hp/l largely due to its tiny .375 liter cylinders (closing on half the size of the Porsche’s).
Bottom line I would not assume that headroom has been left for a future version at this time. I don’t see any real ability to increase revs, friction has largely already been removed to the extent possible and breathing must already be close to the limit. Simultaneously the shadow of tightening emissions regulations looms large. I’m sure more power is available with more substantial changes (I’m betting on a cam change and little else for the RS), but it seems possible that time’s run out for those revisions before the curtain comes down.
02-19-2018, 01:38 PM
#4
Burning Brakes
02-19-2018, 02:08 PM
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02-19-2018, 05:16 PM
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