Cayman GT4: Where are we up 2 now? Déjà vu Edition

[Brian_Innes]

Interesting video Ralph.

To my ears, which btw are not as good as they used to be and will defer to the appraisal of others more qualified. I'm not convinced the GT4 on the clip is a flat-6.

Time will tell.

Brian

 

[MrDemon]

no vids of high revs which I find odd time and time again.

 

[Twinfan]

no vids of high revs which I find odd time and time again.

My thoughts exactly, it's always low revs. F6T from the Carrera anyone?

 

[Motorhead]

Let's not go there again..!

Jeff

 

[ralphmusic]

Jeff,

Deja vu all over again... see below (Chrome translated from German)

QUOTE

So on multiple request here now a little digression to DIY audio analysis:

The audio tracks (or videos with audio track) must be local. Various websites allow the download of Youtube content as an MP4 file. Audacity can read MP4 if the FFMPEG library is installed.

The default representation of Audacity as a waveform is not appropriate, we switch to the spectrogram view. It will then display a waterfall chart in which the time history will be shown from left to right, the low frequencies below, the high ones above. The color expresses the energy that has this frequency in the spectrum, the color scheme can be adjusted.

The resolution of the diagram can be changed, but a higher resolution on the frequency axis degrades the resolution on the time axis and vice versa. A "window size" of 8192 "rectangle" is a good compromise for our purposes. If you want to concentrate on the engine noise and tire squeals, etc. does not want to see, then you should represent the section from 100Hz to 600Hz.

Now you can see lines to every vehicle. There are always several, because no "sound" consists of only one frequency. Rather, the two-, three-, four-fold, etc. of the frequency can be seen. They are only * integer * multiples. How do you know which line is the fundamental frequency? Well, if you see lines at 200Hz, 300Hz and 400Hz, then 200Hz can not be the fundamental frequency, because 300Hz is not an integer multiple. The fundamental frequency is often also the lowest strong frequency (note: in addition to the frequency of the exhaust valves, an engine also produces slightly weaker noises due to the crankshaft revolutions and even weaker ones due to the camshaft). In addition, you can exclude nonsensical variants, if, for example, more than 9000 / min result or visibly forced driving <4000 / min.

Here is a small gallery, what you can see there:

A 911 RSR accelerates and switches to the Rettifilo chicane. https://youtu.be/-I5lwezLlls#t=2m07s



A "GT4" luptens because of Power Oversteer in Adenauer Forest. Even the tire squeal can be seen as an area above 800Hz.https://youtu.be/uoIrIyIDOGU#t=36s



Doppler effect (the gentle downswing at 1:16) at the outset of Parabolica with fast passing of a GT2. https://youtu.be/hbqkZ7IDSqo#t=1m13s



Basically, you have to take into account the Doppler effect when the car approaches or moves very quickly. One sees the effect also with the 911RSR picture, it looks so, as if the later switching operations take place at lower speed --- the effect comes off however by the increasing distance speed. When driving past without luffing / braking / shifting, you can roughly take the average, here about 330Hz. For slower driving by, the error is not so great because of the unknown speed, at any rate this error does not make a 6-cylinder a 4-cylinder.

I could not hear a GT4 or Spyder with more than 200Hz in any video so far. Corresponds to 6000 cylinders with 4 cylinders. With a 6-Ender that would be only 4000 / min, as they would be quite underertourig on the way.

END QUOTE

 

[Brian_Innes]

Ralph,

It may well be alleged that I'm thick, but I've had to read that quote over several times to get the gist. It's a bit like reading the script from the Gendarme Crabtree in Allo' Allo!

The interesting thing for me is the very last sentence of the quote.

Ignoring the "6000 cylinders", which I take it to be 6000rpm, the author is saying the engine note on the videos seem to point to that of a 6-cyclinder engine, according to the revs on pass-by.

I'll defer to more qualified opinions on this subject.

Brian

 

[Motorhead]

I'm with you Brian - and signal processing is my specialty..!

Actually, in his last sentence I think he's saying that the video clip points to a 4-cylinder engine: at 6,000 revs/min a 4-cylinder's dominant 2nd engine order frequency will be 200Hz whereas for a 6-cylinder that frequency would correspond to 4,000 revs/min for its dominant 3rd engine order.

His spectral analysis is rather dubious in my opinion without the inclusion of engine rpm, which is the only means of identifying the actual engine orders which my friend and I did back in May with much more sophisticated analysis software.

For what it's worth I still think that having invested a significant amount of time and resources, Porsche are persevering with the n/a flat-6 for the GT4 despite the problems associated with WLTP. However that's not to say they're not investigating alternatives, and a tuned flat-4 turbo would be a relatively straightforward possibility.

Meanwhile, the rumour-mongers continue to have their say..!

Jeff

 

[981TC]

I'm with you Brian - and signal processing is my specialty..!

Actually, in his last sentence I think he's saying that the video clip points to a 4-cylinder engine: at 6,000 revs/min a 4-cylinder's dominant 2nd engine order frequency will be 200Hz whereas for a 6-cylinder that frequency would correspond to 4,000 revs/min for its dominant 3rd engine order.

His spectral analysis is rather dubious in my opinion without the inclusion of engine rpm, which is the only means of identifying the actual engine orders which my friend and I did back in May with much more sophisticated analysis software.

For what it's worth I still think that having invested a significant amount of time and resources, Porsche are persevering with the n/a flat-6 for the GT4 despite the problems associated with WLTP. However that's not to say they're not investigating alternatives, and a tuned flat-4 turbo would be a relatively straightforward possibility.

Meanwhile, the rumour-mongers continue to have their say..!

Jeff

Going to be interesting to see how this plays out, especially given recent rumours on the new GT3 having a turbo power plant.

https://www.autocar.co.uk/car-news/new-cars/next-gen-porsche-911-gt3-go-turbo

Personally, I’d love another na 6 on the GT4 and Im hoping I’m lucky enough to get one

 

[Motorhead]

I'm not at all sure what those pictures are about Jose. Yet more journalistic fluff I reckon.

A turbocharged GT3? If that's the case then why have the turbo cooling ducts in the rear PU been blanked off?

Jeff

 

[ralphmusic]

..and off we go again..

https://rennlist.com/forums/gt4/1033199-718-gt4-220.html#post15301625

 

[Twinfan]

Interesting. That's the best engine spec they could have gone for in my opinion. The question now is how the WLTP and GPF regulations affect it...

 

[Motorhead]

This speculation is becoming more tiresome than Brexit..!

If Porsche are having problems getting the 4-litre engine through WLTP why would there be lesser problems with a 3.8-litre? Porsche have invested a lot of development time and money in the revised engine and I can't see the logic in them backtracking at this very late stage. If they were going to make a drastic last-minute change I'd have thought taking the flat-4 turbo route would be preferable, assuming that engine isn't throwing up WLTP issues too.

Jeff

 

[Twinfan]

Maybe the change means they can hit their target power figure easier under WLTP regulations with a higher tune on a 3.8 than a lower tune on a 4.0?

It might not even be WLTP related, it could be a marketing move to keep the Cayman "less" than a 911.

Who knows!

 

[Motorhead]

As you say Dave, who knows?

Since you can't even order a new 718 Cayman at the moment there's no point Porsche releasing the new GT4 even if it's actually ready to go, as would appear to be the case from the spy shots. And as we know, delays fuel speculation..!

Jeff

 

[Twinfan]

It depends whether the GT4 is further up the list of the WLTP testing schedule than the existing 718 models - it may be tested before them but I would guess that's unlikely.

 

[Motorhead]

Agreed Dave. I would think that base models would take precedent over a limited-run model like the GT4, especially since the prospective purchaser list is now getting very long according to a very frustrated sales rep I spoke to on Tuesday.

Jeff

 

[Twinfan]

I've just posted this on PH, but for completeness I'll add it here too:

Here's a thought... Under the rules, can the new Clubsport car race with an X51 981 engine if they sell the car to customer race teams? The homologation car is the 981 GT4 and I I assume homologation rules allow cars up to a certain age to be entered into the GT4 series. Would the engine tweaks be allowed under the rule book? If so, then the updated race car doesn't have to bear any relation to the new road car i.e. the new road going 718 GT4 and Spyder can be turbos.

 

[Motorhead]

Dave,

I'm no expert on the GT4 regs but I don't think engine mods are allowed; which is what a 981 Clubsport with X51 would be.

Nice try..!

Jeff

 

[Motorhead]

....

 

[Twinfan]

Cheers Jeff, I thought that might be the case...