mikex25

Coming from the BMW world a tune can definitely bring out 70+ hp and turbo motors are very capable. Reason why it doesn't roll out of the factory with this much power? I am not sure, could be to keep the same motor but different tuning for different model years to sell more cars with less R&D for a new motor. We can agree with this power kit and it's warranty that's already worth its price of admission.

I still think this a great option for those who like the narrow body, got their cars before the GTS came out, or don't like the GTS package.

randr

^^^absolutely, I am one of those that doesn't like the wide body, but generally likes the GTS concept and look.

Some facts and figures for those that aren't really familiar or don't understand the nature of high static compression ratio turbo charged engines. The first figures (highlighted in blue) represent the engine HP calculated from the torque curve in the range 4000rpm to redline. The second figure (in red) is a spot value of HP calculated from the torque curve at 4000rpm.

991.2GTS/X51 408HP (4000-7500rpm) and 308HP @ 4000rpm - the power increase is available across the whole torque curve.
991.2S 375HP (4000-7500) and 282HP @ 4000rpm

991.1GTS/X51 342HP (4000-7700rpm) and 217HP @ 4000rpm - the NA X51 power kit in the 991.1 made a small difference because the kit only increased peak HP over a very narrow rpm range and had little impact on the majority of the torque curve - thus power gains under the curve were small over a pull.
991.1S 338HP (4000-7700) and 213HP @ 4000rpm

991.1GT3RS 387HP (4000-8700rpm) and 199HP @ 4000rpm - compare with .2X51 - note these calculations are relative to crank - if losses are are viewed at the wheel the difference is larger between the .2GTS/SX51 and .1RS/GT3
991.1GT3 365HP (4000-9000) and 185HP @ 4000rpm

Petevb

Also driveability and long term durability, particularly of the turbos.

Typically the approach the aftermarket takes is to over-speed the turbos causing more heat (engine heatsoak, issues in hot weather) and shorter turbo bearing life. How short depends- manufactures tend to be pretty conservative, and sometimes they build significant headroom in (the BMW N54 in the 335i was good for at least "35" hp in the 1M). Tuners tend to push much further by going to the edge of the turbo map, to the point that you can eventually see your turbo bearings go if you put miles on.

Driveability and feel are more "right now" issues. Porsche intentionally limits torque in both its normally aspirated and Carrera turbo models to make the car feel like it's rushing to the redline. Simply cranking up the boost without bigger turbo will make the car faster, but it will also feel like it's "running out of breath" towards redline in the same way many complain about with older turbos. Finally any increase in boost will increase the time between asking and getting full power delivered. This is why some prefer the engine in the non-S 991.2; its lower boost level means it's actually got the sharpest response of the bunch. It's down to personal preference if that's more important than outright power.

Power is cheap these days, and outside of Porsche it's growing exponentially. You can get a 707 hp dodge for 50k, or you can spring for the 840 hp version with a 9.6 1/4 mile @140 mph for less than the price of a base Carrera. Tesla sells a 4 door that'll crack 2.3 seconds to 60 for the price of a Panamera Turbo. It won't be long before even the average Porsche buyer stops asking themselves "how fast can I go for the money" and starts asking that other question- how fast do I want to go. Because as virtually infinite speed gets ever cheaper that question becomes harder and harder to ignore. I first ran into it head on building a 600 hp 944 turbo over a decade ago, and have run into it since many times since- behind the wheel of a 918 or a supercharged viper, etc. When everything is stupid quick it really does come down not to how fast you go, but rather how you go fast. And that's personal preference, but on the street I can say it's slower than I once thought.

If it's me I'm taking this kit over a tune because no tuner's going to do drive-ability as well as Porsche. But I'd also be pretty tempted to leave well enough alone depending on how I was using the car.

evilfij

I agree wholeheartedly with the above from Petevb.

I ordered a base because as fun a stupid fast is (ever drive a new 991 turbo), there is no current production 911 that can be driven remotely close to the limit on public roads without committing a felony. Sure, a 0-60 stop light drag once and a while is entertaining, but absent a track the difference between 370hp and 450hp let alone 420hp and 450hp is largely meaningless. I am sure the kit is great and well thought out etc., but for me the path forward ie the next step is a GT3. And if you want the kit, ticking the box on a new S build is easy enough (albeit $13k).

surquhar

You have it down my friend. Please put a period/and or grammer in your statement. The ******** are out.

randr

For me the combination of drivability and reliability is important - thats what Porsche will deliver. It was obvious the engine was over engineered from the get go - there was always going to be a GTS version and that was going to have to be reliable too.

I don't need to test the depths of the headroom - 550nm and 450 peak HP is plenty of mumbo. On track, you can't play fast and loose with the very high torque in mid-range, particularly on corner exit - more so in the wet. The GT2RS is certainly going to be interesting in that regard

To put it another way, the AWD 991.2 TTS puts down 117Nm/tonne (engine, per driven wheel) on over boost per driven wheel, the 991.2 X51S puts down 186Nm/tonne (engine, per driven wheel)

In terms of headroom, my best guess is about 15nm (not really a guess) per litre (above and beyond GTS spec).......

Petevb

And this is why I avoid the 991 board... First, let's skip the name calling. I'm both an engineer and sometimes automotive author, and I'm here to have a straightforward discussion.

Re response it's fairly simple: For the 488 GTB, for example, Ferrari measures "response time to accelerator" as the delay between the accelerator being fully depressed until the engine gives full power. Obviously this changes depending on RPM, etc, but the more boost you're running the more the turbo needs to spool up in order to deliver that power and hence the longer the delay. If it's a ship and the captain asks for full power how long until the engine fully reacts? Put another way, how long is the rubber band between your foot and the throttle. For some it's an important number.
I used the 1M only as a concrete example of a car manufacture building reliable headroom into their hardware, nothing more. What you've just said supports that point.
Porsche absolutely and intentionally limits torque to provide a top end rush and an early 911S style feel in many of its motors. Particularly with the long stroke engines, ie 991.1 GT3 RS vs GT3 they have gone to great lengths to limit the increase in torque, largely by playing with intake runner diameter and exhaust headers. Because of this when the aftermarket goes looking they do find huge amounts of torque. Simple headers and a tune on a GT4, for example, have been known to increase torque by over 60 lbs feet in places, while gains in the upper rpm range are much smaller. Similarly when Porsche modified the 997.2 GT3 RS engine by stroking it they did not get disproportionately more torque than hp despite the fact that every book, tuner and engine simulator will tell you they should have.

To avoid this they massively oversized the intake runner diameters, cutting low RPM torque. Thus Porsche's 4.0 makes only 25 lbs ft more than the 3.8 at lower rpm. When the aftermarket strokes the same engine and doesn't change out the intake runners such as Sharkwerk's 4.1, they find over 80 lbs feet. This is not because Porsche was incapable of doing the same engineering. I have spoken to Porsche engine designers who have told me as much directly.

Porsche is tuning for engine feel, and while our butts are not very good as distinguishing absolute acceleration they are very good at detecting changes. Falling torque as you approach redline is interpreted as running out of breath, and it's a feeling Porsche has been trying hard to avoid. You only need to look at the relatively low torque on the 991.2 for confirmation.
See "response time to throttle", above. Note that some of the most experienced Porsche reviewers around consider the base 991.2 engine the best of the bunch for this reason.

randr

Petevb - it is absolutely clear that Porsche design engines to respond in a certain way (although there is some chicken and egg in this).

I think this is something they get right - perhaps more so because they focus on integrated response e.g. all key facets of performance working together.

However, its also true the 991.1 GT3 drop off from peak power to redline is greater than that for the 991.2 S/GTS/X51 from peak power to redline. . Its also true that the losses of high revving engines have to be taken in to account - but rarely are.

Valvefloat991

While the aftermarket can always easily find more power in a turbocharged engine by raising the boost, it's clear that reliability margins are sacrificed in the process. The OEMs calibrates their turbocharged engines so that they will survive if a driver fills the tank with regular octane fuel and then proceeds to power up a long hill in top gear at low rpm and full boost on a 115-degree day. The engines won't blow up or overheat and the catalysts won't melt.

When an aftermarket tuner increases an engine's power, this margin, to some extant at least, diminishes. It may diminish less with the 991.2 engine which seems to share the same cooling system, internal engine parts, and intercoolers among the 370. 420, and 450 hp versions. It sure seems like you could simply bolt the GTS turbos onto the base engine and add the GTS software and gain a reliable 80 hp.

Beyond that, you start sacrificing your safety margin. This might not be a problem for a driver who is aware of this and stays away from the boneheaded mistakes that the manufacturer is protecting against, but there is clearly going to be some loss.

And there will obviously be some loss in responsiveness as well. It takes longer to go from zero boost to 20 psi than it does to 10. And bigger turbos spool up more slowly than smaller ones. This is reflected in the GTS, where peak torque doesn't arrive until 2150 rpm rather than the 1700 of the base care and the S. Yes you can tune the engine with a later spark and earlier exhaust valve opening to dump more energy in the exhaust stream, but I suspect Porsche is already doing this as well, so there's probably not much room for the tuners to do more.

As to Porsche limiting the torque of the naturally aspirated engines, I would probably not have stated it that way. It's clear that in the GT engines, the goal is maximum peak power. As we know, the valve timing, port sizes, and intake manifold sizing for optimum breathing at high rpm is not the same as it is for the mid-range. This is true even with variable cam phasing and the various flaps that can alter the intake manifold geometry.

With the GT3 engines developing 125 hp/liter, clearly everything is biased towards high-rpm breathing. I think that's why mid-range torque is more modest rather than any overt limitation on the part of the engine engineers.

By the way, the same is true with high performance motorcycle engines that are making roughly 200 hp/liter and revving beyond 14,000 rpm. These engines also feel like the GT3 does, with no obvious torque curve, but simply feeling stronger the higher you rev them.

Petevb

Let me see if I can get simple points across one at a time:

I'm at say 2k rpm under no load. I have zero boost in the system and the turbo is idling.

I now give it full throttle. Intake opens, exhaust gas is created, the Turbo starts to spin, manifold goes from vacuum to 0 psi. For the sake of argument let's say this takes .1 seconds. Now I continue to build boost. More power is made in the engine, more exhaust gasses are created to spin the turbo, more pressure builds in the intake.

Say I get to 5 psi in .3 seconds (total time) before the wastegate opens. Or I could keep it closed and keep building boost, getting to say 14 psi in .8 seconds. Or go further still and build to a full 26 psi in ~1.8 seconds. That difference of .5 seconds or 1.5 seconds is the extra time I'm talking about- the elapsed time between requesting full power and getting it.

Theses numbers are not entirely arbitrary, they are taken from Ferrari's 488. Ferrari limits boost in lower gears specifically to improve throttle response, and they trumpet their "class leading response" of .8 seconds at 2000 rpm in 3rd gear. The per-gear torque curve that results from reducing boost in lower gears in order to improve response is on the right below, and limiting boost is key to the response impovement.



Now please explain again what you're suggesting? Somehow it does not take any time to build boost? It just magically jumps to 26 psi with zero delay?

J.Ho

mikex25

its a car forum so I could careless about my grammar. I wuickly wrote this in the middle of myself having breakfast on vacation, but I get what you mean.

Petevb

Point 2: Ever ask yourself why mid-range torque is going backwards with newer generations of engines? Why there was some mystical engine technology Porsche developed for the 997 RS 4.0 and then lost to the sands of time, leaving only a gaping hole in the mid-range of the more advanced engines that came after it? Must be impossible to make torque on the newer 9A1 engines...



Yet for some reason the aftermarket seems to fill the hole with little trouble:


How could that be, I wonder?

motobell

Is this kit also for carrera 2 aka base or is there a different kit

R_Rated

This... there was another thread about an 80 hp increase with a tune and no improvement over the expected factory 1/4 mil time. With launch control it's not about the driver either since the driver is simply there to aim.