Nick

regarding future models. Got this from the RT site.

http://www.autocar.co.uk/car-news/ne...ating-supercar

0Q991

Thanks for sharing.

Serge944

640hp for the 650s and anticipated 670hp for the upcoming turbo 458. They better change that "as much as" to an "at least" 600hp.

Should be interesting. They're not going to steal any Ferrari buyers, because, well, they're Ferrari buyers. I don't think they'll be taking any McLaren buyers, well, because at the end of the day it will still be a budget saving parts bin VAG car and not "special enough." How many 911 turbo buyers are going to step up to the plate for a $400k car? I dunno.

But then again, they're Porsche, and it will probably be fantastic.

Nick

What is strange is presently Porsche executives claim they have a 458 beater. It is the 991TTS. So why this obsession with Ferrari?

I also agree that their is a limit to what I am willing to pay for a car. Unless the car is so spectacular that it is must have, I cannot justify paying more the $250,000 for any car. More importantly, where would I use it. As it is I am trying to figure out how best to use the GT3. It shines when revved past 7000rpm's but unless I am tracking it, the opportunities will be brief and limited.

Petevb

Forced induction 4.0L flat 8... If true, I'm curious about the thinking behind this. I see little advantage over 4.0L forced induction flat 6- it'd seem to be longer, not fundamentally lighter, nor fundamentally cheaper. Meanwhile either could make phenomenal power.

Three potential technical reasons come to mind:
1. If room for expansion is needed the V8 could have room to grow to 5 liters or more.
2. The flat eight could make for a more powerful normally aspirated motor.
3. Eights potentially lend themselves to cylinder cut better than sixes- they might be planning to deactivate half the motor to improve economy?

Not sure which of these justifies the development of a new motor... perhaps as the basis for a new race motor/ mezger replacement? Though you'd think they'd want to stick with racing the 911...

Or perhaps they'll simply see cost reductions due to component sharing from the upcoming smaller turbo motors? It does sound like exactly 2x the rumored flat 4.

Serge944

I think V8 makes sense for forced induction too. Smaller piston and, more importantly, shorter stroke for a given displacement, so you can rev higher and make more power at a given boost pressure.

armbar

Looks like a rebranded Audi.

Petevb

But adding revs and top end isn't great for lag, and making the quoted power is far from a problem with forced induction at these displacements. The GT2 RS was making 620 conservative hp from 3.6 liters without direct injection, etc. Thus power wise I'd be thinking about well north of 700 hp before making a new motor made any sense.

The more I think about it, the more I think it's modularity. The Cayman gets 4 cylinders, the 911 six and the 988 eight. 350, 525 and 700 hp respectively, +/- depending on tune...

Guest89

It would be very unlike Porsche to let the V8 from the 918 go to waste with no other applications over which to amortize the initial development cost.

Serge944

I certainly prefer the high revving McLaren tt v8 to anything forced induction from Porsche. It's what the gt2 should be (and may be with the new GT3 RS - we'll see).

Besides, Porsche's torque specifications are not accurate for that car - at all. The peak torque arrives some 1250 rpm past the quoted engine speed and lasts for a range of about 2500 rpm (3500-6000). The McLaren provides peak torque from 3500 to 7000 rpm, for a range of 3500 rpm. This is all without even using variable geometry turbos. The Porsche is an absolute sledgehammer, but the McLaren certainly has a better powerband. Afterall, it traps the same speed through the 1/4 even being 100whp down on power!

Both amazing cars, but I think the higher revving powerplant is the way to go. Besides, with the V8, you can use a flat plane crank and actually make the engine sound good. Porsche's turbo sound is completely soulless.

Petevb

I think the mistake is in assuming that the differences you mention are mainly to do with the engine architecture- Porsche could easily get the power band you're asking for with a flat 6 if they wanted. Instead the differences are primarily down to tuning philosophy- Porsche and McLaren both want their motors the way they are.

Both the Porsche and McLaren are quite short stroke, giving them the ability to run high revs if they choose to. It's slightly harder for Porsche- the longer stroke and larger valves both limit RPM sooner than the smaller cylinders on the McLaren, however this is only a limitation north of 8500 rpm as the GT3s prove. Thus Porsche could choose to roughly duplicate the McLaren's power curve (below) if they wanted to, mainly by selecting a different cam profile, changing the intake runners and fitting a smaller turbos:

Above you can see that they chose a different direction, fitting larger turbos to make more peak power, but still spooling it earlier than the McLaren despite a smaller engine displacement. If they'd started with something like the GT3 motor, however, which would be almost identical to the LFA curve but 15% lower, you can see it'd be easy to end up in the middle where the McLaren is.

Each strategy has its merits, but I suspect the direction chosen came down largely to feel- Porsche wanted its car to feel turbocharged with that big torque hit, while McLaren preferred their car did not.

It's clear neither motor has reached its absolute potential- McLaren could easily add direct injection, a variable cam and turn up the boost, while the GT2 RS also has at least DI and an ~11% displacement increase before it's close to topped out. In either case you get to motors that put out close to 700 whp with a number of different power curve options.

Hence my question- if all the different power curves are available without making a new motor, what's the real driver for the flat 8 with these reported power levels? And remember we're talking flat 8 here, not V8. V8s tend to to be slightly lighter due to the inherent rigidity of the block. They are also narrower, so easier to package, but usually with a slightly higher CG.

kosmo

exactly.

Serge944

I would take Edmund's dyno chart with a serious grain of salt. You cannot dyno a McLaren on a 2WD dyno and produce linear power - you have to do it on an AWD dyno, just like the 991 GT3. This is why the torque curve is wrong.

I don't think the turbos have anything to do with peak power. The power difference you are seeing is a result of 17.5 vs 23.5 psi of boost (thats 34% more). The chart below is what happens when you run 23 psi on the m838. AT WOT, you're always making peak power through every gear. I can't support your notion that a shorter power band was Porsche's strategy. It just is what it is - a glorified 911 turbo engine. You can only do so much with 6800rpm. But still an amazing car!



Black line is representative of stock output when dynoed properly:

Petevb

Turbos must be sized for the power level- significantly more power requires larger turbos. You can't turn up boost infinitely to make more power- on a correctly sized turbo this only works within a small range, beyond which you need a larger turbo which has more rotational inertia and inherently brings with it additional lag.
Obviously the 911 is making more power because it's running more boost, but we can see because it's able to make more power that the turbo is larger. Increase the McLaren's turbos to support the same peak power and you'd also increase the McLaren's lag.
First, the below isn't the dyno of a McLaren at all. It's a 5.5 Liter Mercedes twin turbo V8. Let's try to stay accurate...
http://www.hennesseyperformance.com/amgglv8bi.html

Second, the below isn't the result of increasing absolute engine pressure (1 bar atmospheric + boost pressure) by 17%. Torque is up 40% at the 90 mph point, not something you'll see by only cranking the boost that amount. Instead it looks like the tuner is turning up the boost much further, then probably intentionally ramping it down, perhaps to avoid overspeeding the turbo too much.

This stuff is all fairly straightforward to get a handle on with basic engine simulation software, something I've used when doing cam selection and engine design, etc. You can easily use cams to push the 911 powerband up, and the factory did exactly that with the GT2 Evo, GT1, etc.


It is a 911 turbo engine, and there is nothing wrong with that. However the 911 engine is immensely capable- there is a reason they won LeMans over a dozen times, almost exclusively in turbocharged form. There is nothing limiting it to 6800 rpm, and in fact both the factory and aftermarket tuners have built turbo engines that operate well beyond 7500 rpm. There are solid reasons to do this, and solid reasons the factory chose not to for the current motors, but none of them have to do with 6 vs 8 cylinders.

mikes603

Good read, thanks