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What, like virginity? Yeah, a high-revving sports car tends to do that.
OK to put it another way - its what gets to the ground that counts. The current GT3 at 8800RPM has losses of around 120HP................................................................... ..............................
OK to put it another way - its what gets to the ground that counts. The current GT3 at 8800RPM has losses of around 120HP................................................................... ..............................
The GT3 does not in any fashion lose 120 HP from the crank to the ground.
The main reason there is this huge push for power is because everything is getting heavier. 500hp on 3200lbs is 6.4lbs/hp. 430hp on 2350lbs is 5.4lbs/hp. 500hp in 2000lbs is about perfect.
Randr, I understand why you're focused on that single graph, but have you considered all the rest of them? Both the 997 RS 4.0 and 991.2 GT3 have pulled 458-460 hp at the wheels between 8k and 8.25k on Dynojets (vs a 991.2 Carrera S at 380 whp, etc). Think what you will about that Dyno's absolute accuracy, they are highly repeatable when set up correctly; the many strong results (on many different dynos) can't be reconciled with the extremely high driveline losses you're suggesting. If you have other solid GT3 dynos that suggest high losses let's take a look, but GT3's typically outperform on wheels dynos vs what's expected at the crank.
High RPMs are not inherently less efficient post engine; gear design theory explains why and examples abound, from 14.2k RPM motorcycles (~10% loss) to 20k rpm F1 cars to 18k rpm Tesla). In fact there are significant weight and size advantages to lower torque, higher RPM gearboxes, as the torque that individual gears need to withstand (and hence their size and weight) go down. V8 era 7 speed F1 gearboxes weighed just 80 lbs and transmitted 800 hp largely because they didn't need to transmit any more torque than an anemic hot hatch until their final stage. That said if a gearbox isn't designed for high rpm you can easily get high pumping losses- wet clutches, lube oil pumps and hydraulics for shifting all need to be designed for the RPM range of the engine to avoid excess losses; perhaps one reason the PDK GT3 loses a couple MPH to the manual.
Inside the engine is a different matter, and it's quite challenging to avoid pumping losses caused by moving so much air and fluid around rapidly. Fortunately motorsports (and in particular F1) has now largely addressed that too, pulling enough vacuum in the crank case that there simply isn't air to move. This helps result in the 50%+ thermal efficiency (at 15k rpm) that modern F1 engines have recently surpassed.
PeteVB -I don't have anymore of the new GT3
How about a GT4 instead to illustrate the point - losses are not a constant percentage and are non - linear (even though they can look linear on poorly scaled plot)
Note that at 6000RPM the losses for both the GT3 and GT4 are about 60HP. From around 7500RPM the GT3 losses start to build and accelerate in a visibly non-linear fashion.
There are a lot of good answers here. I think the simplest way to get an idea of the situation is to just look at hp/liter. 520 hp from a 4 liter engine gives you 130 hp/liter. That is quite high. The Ferrari 458 and 812 are both in the low 120s and the FXX K is around 135.
Ultimately, displacement is really the most important factor in achieving reliable NA power.
It’s a very valid question, and having looked into that question in some detail I came away impressed. Porsche stopped at 4.0 liters for reasons having to do with race classing rather than technical limits. The 4.0’s cylinder liners are hence much thicker than say a ‘Vette’s or race cars, and even at 4.1 liters there’s some margin in the Sharkwerks build vs common state of the art. The pistons are large for the rpm but reasonable given the race spec components.
As far as overall reliability no aftermarket program can hope to match factory testing, but good tuners have the major advantage of hindsight: they get see what breaks in the real world on the factory cars then design specific solutions to those issues after the fact. Nothing’s perfect, and there are a half-dozen known weak points on the 997 RS 4.0 that will likely cause issues under heavy track use. In that light I’d trust their 4.1 a similar amount to the factory effort. I would not say the same for the vast majority of tuners, however.
On that front I have more faith in the new GT3 engine than any of the previous versions given the testing and commonality with Cup cars. Time will tell if that’s well placed.
I'm not sure the bolded statement is true:
Cup Car = Porsche spec series; can run whatever they want to
GT3 R = GT3; naturally aspirated engine displacement in excess of 4.0L allowed (witness Mercedes NA 6.2L V8, Audi 5.2L V10, etc.)
911 RSR = GTE; forced induction up to 4.0L; naturally aspirated up to 5.5L (Corvette)
Cup Car = Porsche spec series; can run whatever they want to
GT3 R = GT3; naturally aspirated engine displacement in excess of 4.0L allowed (witness Mercedes NA 6.2L V8, Audi 5.2L V10, etc.)
911 RSR = GTE; forced induction up to 4.0L; naturally aspirated up to 5.5L (Corvette)
03-12-2018, 12:05 AM
