How much NA power is technically possible from a flat six?
03-12-2018, 08:16 PM
#76
I wish Porsche could have brought back the flat 8 at some point....
03-12-2018, 09:34 PM
#77
Drifting
4.4 FI would have the BMW M6 right on the limit; the M8 GTE has a 4.0L engine so now it actually conforms to GTE/GTLM rules
I spent a few minutes talking to Atherton on Saturday at Amelia but forgot to bring up the farcical M6 GTLM car
On a related note, Porsche needs a signal victory for the new RSR - hopefully Sebring and Le Mans this year. Otherwise ...
I spent a few minutes talking to Atherton on Saturday at Amelia but forgot to bring up the farcical M6 GTLM car
On a related note, Porsche needs a signal victory for the new RSR - hopefully Sebring and Le Mans this year. Otherwise ...
03-13-2018, 03:06 AM
#78
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Apologies for stating the obvious, but there is a very rigid relationship between torque, revs and power. It's like how tall your glass is, how wide it is and how much water fits in it. So, for example, a 9K rpm engine with 300lbs/ft of torque is the SAME as 6K RPM engine with 450lbs/ft of torque in every way because you can get from one to another with just a 1.5 reduction gear. And if GT3 were making 450lbs/ft in the working range (6.5K-9K) while still revving to 9K, it would have made way more than 500HP.
03-13-2018, 03:15 AM
#79
Drifting
Apologies for stating the obvious, but there is a very rigid relationship between torque, revs and power. It's like how tall your glass is, how wide it is and how much water fits in it. So, for example, a 9K rpm engine with 300lbs/ft of torque is the SAME as 6K RPM engine with 450lbs/ft of torque in every way because you can get from one to another with just a 1.5 reduction gear. And if GT3 were making 450lbs/ft in the working range (6.5K-9K) while still revving to 9K, it would have made way more than 500HP.
Or is ~340 really the max, given the formulas posted earlier?
03-13-2018, 09:42 AM
#81
03-13-2018, 12:55 PM
#82
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But with much higher revs, that gives you the ability to lower the gearing more which in turn improves the torque to the ground (gearing acts as a torque multiplier). This is one of the reasons that the NA 4.0L in the GT3/RS pulls as hard as some much larger and torquier motors that don't rev as high.
03-13-2018, 01:17 PM
#83
Drifting
03-13-2018, 07:19 PM
#85
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Meanwhile the rest of the time I felt like a shark stuck in a fishbowl- give me a Boxster Spyder 9 days out of 10. So I'm largely past wanting "more" for its own sake, and I suspect that as it becomes more accessible others will come to the same conclusion. Sure there will always be some who're playing a clubhouse game of Top Trumps and others who are chasing lap times, but for the rest of us extreme experiences can be had with much less power than is already fairly easy to buy.
03-17-2018, 09:44 AM
#86
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.
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.
Take a look at this graph (generated on a maha) and it becomes clear that the increasing friction being measured has far more to do with road speed than RPM. You can clearly see that in 2nd gear increasing revs has no effect on friction, though at high speeds it looks like it does. Basically whichever car is going slower (dyno speed) will produce “lower losses”, so typical dyno practice of using whichever gear is closest to 1:1 will increase speeds and hence disadvantage whichever car revs high. This is why when I dynoed my car (on a hub mounted dynopack, better for this purpose than a maha) the race team operators made it clear that the loss calculated friction measurements were only relatively (same gear, same car) rather than absolutely useful.
Other reasons driveline losses must be viewed with skepticism: estimates are generally made using a “coast down” tests. Take the engine up to max rpm, clutch in then measure how the transmission brakes the already spinning wheels/ drum. Unfortunately many variables are different in this situation. Chief among them for the speed related results above is aero drag, but clutch drag, the gears being loaded in reverse (important because Porsche uses hypoid gears, which are directional and have different losses in one direction vs the other) and other factors are both important and different than on the road.
Back to the point and repeating, there is nothing inherent in higher rpm engines that means well designed gearboxes will have higher losses, and the many dynos like this give the lie to the idea that power to the wheels on GT3s is inherently falling off due to climbing friction.
Last edited by Petevb; 03-17-2018 at 02:32 PM.
03-17-2018, 09:48 AM
#87
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)