I posted about this a few months back but there is more detail available now.
https://rennlist.com/forums/993-turbo-forum/366805-vrus-can-you-comment-on-this.html

the 997GT2 boosts at max 1.4bar which is 0.2bar higher than the 997tt. 1.4bar sounds like a lot for only 530hp but the high boost is part of the trick in the new expansion manifold system.
I have read the following many times and think I am begining to understand what is happening. Perhaps our cleverer RLers can explain in layman's terms the process which leads to needing 1.4bar to produce only 530hp

 

Is the GT2 IC improved?
Seems like they need very efficient IC for this to work.

 

this resonance tuning is a crock. The resonance is going to change at difference engine speeds anyway. The GT2 uses the same VTG compressors as the 997tt despite what Porsche may be alluding. The only difference may be some kind of pre-load circuit for launching. The Gt2 is also has no real headroom for quick tuning, since it the engine setup is essentially a stg 2 997tt

 

As far as I know, the GT2 has larger than 997T turbochargers. This was one of the issues involved in the Techart scandal with Porsche.

 

1.4 bar for 530 hp means you are already at the edge. Considering the stock 997tt only boosts to 1.2 in midrange and always drops to 1.0 at higher revs and manages 480hp, I think it is clear whatever they are calling the modified VTG is not going to be a bigger compressor - if it is any bigger, it is going to be a marginal difference with almost the exact same compressor map.

 

But doesn't it say above that the expansion effect "only works" at certain revs anyway ? How do you know its a crock ?
Are they lying then ? How do you know the compressors are the same ?

This is the point I am looking for explanation on, the 1.4bar seems to be handled (in heat terms) differently by the 997tt engine thanks to the Expn manifold removing the usual heat which would be generated at this level of boost... If the compressor IS bigger (you say not ?) then you can't compare directly with the 997tt engine, throw in the expn manifold and the relative boost levels are meaningless....

FWIW 480hp at 1 bar already points to an elevated (temperature) inlet charge, typically a K24/26 993tt engine makes 480hp at 1 bar (with a CR of 8:1) so it seems the VTGs are already over heating the air (relatively) ?

 

TB,

all tubing produces a resonance effect no matter what. The question is why Porsche would market such a thing in the Gt2 when it exists already in all of the other intakes they build? At what specific rpm are you going to make the "expansion" effect occur in the Gt2 and why?

In regards to the VTG claim, I use Porsche's own numbers and engine dyno plots to see that the Gt2 has the EXACT same torque plot as a regular TT in overboost mode. The regular TT puts up 505ft/lbs from 2100 rpms to roughly 4000-4500 rpms at 1.2 bar. The GT2 has the exact same torque curve shown by Porsche. Given the same curve either the compressor in the Gt2 must have nearly the same flow map as the TT compressor, or Porsche publishing a simplification/underestimation of the torque of the Gt2.

For the expansion intake and larger VTG compressor to be realistic, the GT2 should produce its power at less than 1.4 bar.

 

Aren't they saying that the expan manifold does away with the resonance (which is caused by the compression) and the result is that the cylinders are filled with "slightly less air in the expansion phase than during the compression phase" which is compensated for by that increase in boost -the resulting increase in IAT is "dealt with" by the I/Cs (implies but doesn't specify that the I/Cs are more efficient than 997tt ?
I don't think you can make a call on the turbos simply by looking at the two torque curves in isolation, there are (according to Porsche) other things going on
Do you also believe that Porsche's claim of resulting 15% fuel consumption reduction is a crock ? surely they will get found out ?

 

If you look thru Porsche history the "GT" cars and special edition cars had larger turbochargers.

K24 vs K16's.. With the 965 you have the 7006 vs 7200. It will just be a matter of time before we see the turbochargers on the new GT2.

 

I don't understand the point of heating up the intake charge with 1.4 bar only to then cause a intake pressure drop and subsequent loss of boost prior to combustion. The heat is still getting turned up in the turbochargers and subsequently putting additional load on the cooling systems of the car, and driving up the EGT's which are very dangerous for the VTG mechanism. Also, if you simply eliminated the drag of the AWD in the TT and stripped 300 lbs (nearly 10% of the weight), would you not expect a similar reduction in fuel consumptions in an otherwise stock TT? While this new intake system may somehow increase some efficiency, to ignore the other obvious large factors of 2wd and weight loss is a bit misleading for Porsche.

 

My thoughts exactly - just can't grasp how the "expansion" bit manages to overcome the extra heat of the 1.4bar
Is it 1.4bar just after the compressor and in the "narrow" part of the intake pipe, with the "expansion" bit allowing the real boost pressure to drop slightly as the air expands into the combustion chambers so the "real" boost pressure of the "expanded" air availble may be back down around the 1.2bar mark ?

 

TB,

we are on the exact same page. Imagine "innovating" such a manifold to optimize "expansion" cooling in just one narrow part of the power band, versus simply incorporating a more efficient intercooler (a much larger and effective "expansion chamber") which would benefit the entire power band with hopefully less pressure drop. According to my Service Technik manual, the IAT and boost sensors are both just upstream of the throttle body.

 

I don't know guys, I think Porsche is smarter than what you're imagining is going on. I think if they say 1.4 bar, then it is 1.4 bar that the intake/combustion chamber 'sees' dispite the 'expansion and compression' that goes on. I don't think the pressures change, just the volume depending on temp. If you look at the blue 'dot' - I assume they represent molecules. Although the density of the dots change as you go through the intake port, the density with in the combution chamber is the same, just at a lower temperature. Pressures can remain the same while density/volume changes. (if I remember by physics correctly, I could be wrong - I'm a MD not an engineer)

 

I also think the 15% improvement in efficiency is whether this technology is used or not vs a regular 997tt weight vs a gt2 weight.

 

PV= nRT or P = nRT/V

P= pressure
v= volume
n= # of moles
R= ideal gas constant
T= temp

The only way to keep pressure constant while decreasing temps and keeping volume the same is to increase the # moles of gas. The pressure sensor is in front of the expansion chamber - there has to be a pressure drop in expansion. Regardless, the extra heat is still going to be added to the intake and to the turbos, which effectively could negate the theoretical benefits.