So, now that the GT4 specs are finally known....

So, now that the GT4 specs are finally known....

Poll: So, now that the GT4 specs are finally known....

Total Members Polled: 158

I'd take a 997.1 GT3 please: 33%
I'd take the GT4 please: 67%
Author
Discussion

Mario149

Original Poster:

7,750 posts

177 months

Monday 9th February 2015
quotequote all
NewExigeS said:
Thanks for providing this data, very interesting.

How did you get it btw?
You can match the dyno charts, in gear speed curves and gear ratios from the Porsche car handbooks i.e. choose the speed you're considering, match it to a gear on the in gear chart, look up the gear ratios to find find the rpm, use the rpm to get the torque, use the gear ratios to get a multiplier for the torque to get thrust. then plot the thrust (force accelerating the car) against speed. Then repeat many times for different speeds (say every 5 mph) on a spreadsheet. If you're comparing different cars you can bring their weights (masses technically) into it to account for any differences in how much they weigh e.g. for a given thrust, a car weighing 10% more will accelerate 10% less since Acceleration = Force / Mass

At least that's how I'd do it!

fioran0

2,410 posts

171 months

Monday 9th February 2015
quotequote all
I have a rather sprawling spreadsheet that I use on my Cups. I made it up to help when looking at regearing options etc over the years though it can also be useful for knocking out stuff like the above once in a while.

In short it uses the known engine power curve to calculate the force available for accelerating the car across the entire rev range, for each gear, taking into account things like gear ratios, final drive, tyre size etc.
It also calculates velocity across the entire rpm range for each gear given the same data.
From this one can generate a graph of force versus velocity by overlaying the data for each gear. Usually I use a graph where the lines for each gear simply show as several individual lines on the one graph.
It is of course possible to make the graph type posted here where the data is shown as one continuous line by just adding in a couple of extra steps.

To adjust for weight, use Force = Mass x Acceleration, the known force data and the known mass of the car to calculate acceleration across the rev range. This second graph simply had the acceleration data replace the force data used earlier.

Edited by fioran0 on Tuesday 10th February 00:47

fioran0

2,410 posts

171 months

Tuesday 10th February 2015
quotequote all
franki68 said:
So looking at that , the gt4 will accelerate in a similar manner to the 997gt3.1 ?
More than adequate for my use
Yeah, it looks like they should be pretty close in straight line performance.
The expected ring time of 7.40 given by AP for the GT4 versus 7.42 for the 997.1 GT3 back in 2006 is really quite interesting in that light. I am looking forward to seeing what it officially posts there, though admittedly because I am a nerd.
My curiousity regarding what new cars (in general) are really bringing to the table has been itching at heightened levels since the Jack Olsen video of his car and the 991 GT3 around Willow Springs raised some interesting questions.
The GT4 has 8 years or so worth of advancements in chassis manufacturing/materials, tyre technology, PASM development, electronics such as torque vectoring and the likes going for it over the 997.1.

Harris_I

3,225 posts

258 months

Tuesday 10th February 2015
quotequote all
fioran0 said:
The GT4 has 8 years or so worth of advancements in chassis manufacturing/materials, tyre technology, PASM development, electronics such as torque vectoring and the likes going for it over the 997.1.
Just shows how exceptional the 997 chassis was. I wonder what it'll post at the 'Ring on passive dampers and the latest Cup tyres. We should set a PH challenge for Steve Rance...

The 996 Cup was also very capable against much more modern machinery in its class (Maserati MC, Ginetta G50, Aston GT4) and managed to trouble the gentleman drivers in the class above (Ferrari 430 Challenge cars... before they inevitably suffered a breakdown). All without electro-trickery and flappy paddles.


NewExigeS

423 posts

125 months

Tuesday 10th February 2015
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With a longer wheel base than a 991 GT3, shorter over hangs, dropped by 30mm, 90kg less mass to lug around, huge Cup 2 rubber, 991 GTS suspension parts and brakes, will the GT4 handle better than the 991 GT3?, and possibly all previous GT3s?

V8KSN

4,711 posts

183 months

Tuesday 10th February 2015
quotequote all
NewExigeS said:
With a longer wheel base than a 991 GT3, shorter over hangs, dropped by 30mm, 90kg less mass to lug around, huge Cup 2 rubber, 991 GTS suspension parts and brakes, will the GT4 handle better than the 991 GT3?, and possibly all previous GT3s?
Possibly and I hope it does!

I hope it gets rave reviews and is lauded as a great drivers car with a heavy focus on feedback as opposed to the speed it can achieve.

It would mean there is a NEW Porsche to want to own, and that can only be a good thing.

Steve Rance

5,435 posts

230 months

Tuesday 10th February 2015
quotequote all
NewExigeS said:
With a longer wheel base than a 991 GT3, shorter over hangs, dropped by 30mm, 90kg less mass to lug around, huge Cup 2 rubber, 991 GTS suspension parts and brakes, will the GT4 handle better than the 991 GT3?, and possibly all previous GT3s?
The longer wheelbase of the 991 GT3 is one of the reasons that the 991Cup is no quicker than the 997Cup. Whilst a long wheelbase is more advantageous at faster circuits like the ring, it does not suit the more typical ciruit.

A longer wheelbase may help a car post a decent ring time but I'll take a shorter wheel base every day because it's much easier to rotae the car.

hondansx

4,562 posts

224 months

Tuesday 10th February 2015
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Harris_I said:
fioran0 said:
The GT4 has 8 years or so worth of advancements in chassis manufacturing/materials, tyre technology, PASM development, electronics such as torque vectoring and the likes going for it over the 997.1.
Just shows how exceptional the 997 chassis was. I wonder what it'll post at the 'Ring on passive dampers and the latest Cup tyres. We should set a PH challenge for Steve Rance...

The 996 Cup was also very capable against much more modern machinery in its class (Maserati MC, Ginetta G50, Aston GT4) and managed to trouble the gentleman drivers in the class above (Ferrari 430 Challenge cars... before they inevitably suffered a breakdown). All without electro-trickery and flappy paddles.
Proof of this?

Watched Blancpain at Spa and a like-for-like 997 (GT4) against a comparable GT4 was no quicker. Ultimately, that is the point; GT3 and GT4 are meant to be equalised.

Moreover, i've raced against 996s and they have been signficantly slower than 997 Cup cars. However, the 997 Cup has way more aero than the likes of a Ginetta so is an unfair comparison. In my experience a G55 is as quick as a 997 Cup but far cheaper (they are made like s**t though).

Mario149

Original Poster:

7,750 posts

177 months

Tuesday 10th February 2015
quotequote all
Mario149 said:
NewExigeS said:
Thanks for providing this data, very interesting.

How did you get it btw?
You can match the dyno charts, in gear speed curves and gear ratios from the Porsche car handbooks i.e. choose the speed you're considering, match it to a gear on the in gear chart, look up the gear ratios to find find the rpm, use the rpm to get the torque, use the gear ratios to get a multiplier for the torque to get thrust. then plot the thrust (force accelerating the car) against speed. Then repeat many times for different speeds (say every 5 mph) on a spreadsheet. If you're comparing different cars you can bring their weights (masses technically) into it to account for any differences in how much they weigh e.g. for a given thrust, a car weighing 10% more will accelerate 10% less since Acceleration = Force / Mass

At least that's how I'd do it!
Posting here as well as the other thread for reference...

Here's my effort for a version of fioran0's acceleration chart. Points to note:

1) It accounts for weight of the cars as per the other graph does
2) It uses the gear ratio figures to calculate km/h per 1k rpm, referenced on speed in 2nd gear for each car at redline (6.5k in the 993, 7.8k in the GT4, 8.4k in the GT3). I do not have gearing info for the GT4, but AP seemed to say it was the same as the GTS, so I have assumed it will do the same speed speed in 2nd gear as the GTS, just at alightly higher revs as it goes to 7.8k rather than 7.4k i.e. it has a slightly shorter final drive. If it doesn't and the gearing is *exactly* the same as the GTS, it has a very negative impact on performance so this is the "best" case
3) It doesn't account for drag, but I'm working on a rough calc to include it, not sure it'll bring much to the party though
4) Acceleration on y-axis is plotted as a percentage of the max acceleration achieved in 2nd gear in the 993 NVR - I figured that 2nd gear shove is where we subconsciously "butt dyno" a car on the road so it seemed a useful normlizing figure.
5) Torque figures used in the calcs were read off factory dyno charts from the owners manuals every 500rpm on each rev range with the 250rpm intervals extrapolated as a mid value between the 2 points either side

Any questions, fire away.

Enjoy....



It's not beyond the realms of possibility I might find calc errors, but will update the chart if I do.

If anyone has exact gearing data for the GT4 let me know and I'll update the chart if it's diff to what I used





Steve Rance

5,435 posts

230 months

Tuesday 10th February 2015
quotequote all
hondansx said:
Proof of this?

Watched Blancpain at Spa and a like-for-like 997 (GT4) against a comparable GT4 was no quicker. Ultimately, that is the point; GT3 and GT4 are meant to be equalised.

Moreover, i've raced against 996s and they have been signficantly slower than 997 Cup cars. However, the 997 Cup has way more aero than the likes of a Ginetta so is an unfair comparison. In my experience a G55 is as quick as a 997 Cup but far cheaper (they are made like s**t though).
The 996 Cup is about a second slower than the 997 on average. Say just under on a short circuit and about 1.5 on a longer one. A lot of that time is entirely down to the flat shift sequential in the 997. I drove a bog standard 996 Cup in the Silverstone 24 hours in 2008 and for most of the race we were running 3rd over all leading Moslers, 996RSR's etc.. The car didnt even have a cup engine, just a standard 996 Gt3 engine taken from a road car. The Aston GT3 car made it's debuit there. We thought 'Christ this thing looks amazing, we dont have a chance' Lovely prep, looked and sounded lovely. We ended up lapping it about 20 times. Towards the end of the race, one of our drivers had an off and we lost a lot of time. Still came 7th over all. The day after, the owner of the car did a track day in the same car. It just plodded around all day - Amazing!

The 997 was quicker and easier on the tyres - but more difficult to drive. The GT4 versions are horribly compromised. They ere not designed to be competitive within those regs. If they are raced in the spec and on the tyres designed for them, they are incredibly fast. I Always managed to stick a bog standard 997 Cup on pole in the GT cup against far more exotic machinery. They are small, behave well under braking and - if you know what you are doing - easy to rotate. Devistating on exit.

The 991 cup is no quicker than the 997 cup. An embarresment that this year Porsche will/must undo. Probably by stickier tyres and a different gearbox/ratios. The road 991GT3 is however much quicker than the 997GT3. The difference being mainly gearbox, electrical driving aids and a Torque vectoring diff. In standard road car spec, these advantages are substantial but whist the more analogue chasis of the 997 responds immediately to tuning, the 991 will be much less inclined to as bypassing the electronic systems will take it a step backwards so any analogue tuning solutions will need to be radical from the outset if a performance gain is viable. Take the diff on the 997 for example. A few simple upgrades to the Diff will make substantial gains in performance. There are no such gains to be made with the 991 Diff. Mess with that at your peril.

I've know that there was a lot more to come from a 997 GT3 since I raced the Cup version and then jumped into the raod car. The dynamic differences between the 996 GT3 and 996 Cup are much smaller. However, the 997 GT3 has all of the basic components to be incredibly fast and much closer dynamically and in terms of performance to the 997 Cup car.

But this is a different story and something that should not cloud the coming of the Cayman GT4 in any way. Surely the Cayman should be applauded for it's individuality and should be judged for what it is rather than subjectively against what it isnt.

A cayman can never be a 911 and a 911 can never be a Cayman. In my opinion, it is the 991 that may be the meat in the sandwich.





bcr5784

7,102 posts

144 months

Tuesday 10th February 2015
quotequote all
While not disagreeing with anything Steve is saying, it's often difficult to make meaningful statements about the genuine pace of cars in most endurance GT racing at the GT3 level

1) Because the standard of drivers is very variable - and teams are normally not allowed to run a team of professional drivers.
2) "Gentlemen" drivers generally get closer in performance to their professional team-mates if they have ABS and sequential boxes. Professional drivers generally gain much less from such aids.
3) The organisers attempt to equalise performance of the various car models either by restricting power, raising the minimum weight, by limiting grip either by restricting ride height or suspension mods allowed BUT
4) Teams sometimes sandbag in qualifying to avoid this occurring
5) Porsches are more fuel-efficient than much of the opposition (particularly Moslers), so while often not as fast outright as some of the opposition may still outpace them overall.
6) Even in the race cars may run somewhat below their ultimate pace either for reliability reasons (keeping off kerbs, limiting revs) or tyre degradation reasons.


Edited by bcr5784 on Tuesday 10th February 17:38


Edited by bcr5784 on Wednesday 11th February 07:17

fioran0

2,410 posts

171 months

Wednesday 11th February 2015
quotequote all
Just to add in some more.

Its 100% not double wishbone at the rear. Its still struts all round for the GT4 as with the rest of the range. The lower control arm got beefed up as did the sway bar mounting at the back end. No mention that the rears are split design to allow more static negative camber though. Only that the front are of a split design.

The diff is also the zero preload, 27/22, do nothing diff thats in the rest of the Cayman range. (Hopefully the phone to GT gears will be heating up)

The gear ratios are indeed exactly as per the manual transmission in the Boxster and Cayman GTS.

Porsche figures are 4.2s 0-60 mph, 4.4s 0-100 km/h, 1/4 mile 12.5s, top speed 183 mph.


Steve Rance

5,435 posts

230 months

Wednesday 11th February 2015
quotequote all
bcr5784 said:
While not disagreeing with anything Steve is saying, it's often difficult to make meaningful statements about the genuine pace of cars in most endurance GT racing at the GT3 level

1) Because the standard of drivers is very variable - and teams are normally not allowed to run a team of professional drivers.
2) "Gentlemen" drivers generally get closer in performance to their professional team-mates if they have ABS and sequential boxes. Professional drivers generally gain much less from such aids.
3) The organisers attempt to equalise performance of the various car models either by restricting power, raising the minimum weight, by limiting grip either by restricting ride height or suspension mods allowed BUT
4) Teams sometimes sandbag in qualifying to avoid this occurring
5) Porsches are more fuel-efficient than much of the opposition (particularly Moslers), so while often not as fast outright as some of the opposition may still outpace them overall.
6) Even in the race cars may run somewhat below their ultimate pace either for reliability reasons (keeping off kerbs, limiting revs) or tyre degradation reasons.


Edited by bcr5784 on Tuesday 10th February 17:38


Edited by bcr5784 on Wednesday 11th February 07:17
Yes agreed re endurance. My experience is mainly in sprint racing which - although it is very happy to run in endurance - is what the 996 and 997 cups were designed for. Very effective in spirit as well as endurance format.

ras62

1,086 posts

155 months

Wednesday 11th February 2015
quotequote all
A 54l fuel tank, is this correct?

theRossatron

1,028 posts

231 months

Wednesday 11th February 2015
quotequote all
ras62 said:
A 54l fuel tank, is this correct?
yeah and 64l is a no cost option.

ras62

1,086 posts

155 months

Thursday 12th February 2015
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theRossatron said:
ras62 said:
A 54l fuel tank, is this correct?
yeah and 64l is a no cost option.
That's more like it. The first tick on the option list for most people but I could see a few owners being unaware and getting caught out with the smaller tank. The default option should be the larger tank imho.

theRossatron

1,028 posts

231 months

Thursday 12th February 2015
quotequote all
ras62 said:
That's more like it. The first tick on the option list for most people but I could see a few owners being unaware and getting caught out with the smaller tank. The default option should be the larger tank imho.
Apparently it's default to keep the quoted weight figures down.

Harris_I

3,225 posts

258 months

Thursday 12th February 2015
quotequote all
hondansx said:
Proof of this?

Watched Blancpain at Spa and a like-for-like 997 (GT4) against a comparable GT4 was no quicker. Ultimately, that is the point; GT3 and GT4 are meant to be equalised.

Moreover, i've raced against 996s and they have been signficantly slower than 997 Cup cars. However, the 997 Cup has way more aero than the likes of a Ginetta so is an unfair comparison. In my experience a G55 is as quick as a 997 Cup but far cheaper (they are made like s**t though).
I can't add to Steve's response other than to say my evidence is first hand and anecdotal, and therefore not scientific in any way. Also I may not have explained myself well first time: I wasn't suggesting the 996 was as quick as the 997. I was saying the basic platform was just brilliant: brilliant enough for an 8 year old car to slug it out toe to toe against brand new cars in the same class (which obviously wouldn't include the 997).


Mermaid

21,492 posts

170 months

Thursday 12th February 2015
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theRossatron said:
Apparently it's default to keep the quoted weight figures down.
Same with CR's, just fill less.

fioran0

2,410 posts

171 months

Thursday 12th February 2015
quotequote all
Steve Rance said:
Yes agreed re endurance. My experience is mainly in sprint racing which - although it is very happy to run in endurance - is what the 996 and 997 cups were designed for..
Just to add on to what others have said, I am about 1 second slower per lap slower at somewhere like Laguna Seca in a 996 versus a 997 Cup with lap times in the order of low-mid 1.3X's. Somewhere like Lime Rock where its sub 1 minute laps I find that my lap times are very similar regardless of which I am in. At a longer track like VIR where lap times are in the high 1.5X's I find not quite 1.5 seconds difference in my times depending on what car I am in.
Quite a different driving experience between the two platforms of course but thats what I find the actual pace difference to be. This seems in line with what others are doing.
This is for cars in GTC class form; ie standard Cups as delivered by the factory.
The balance of performance stuff is really only needed for series where there is a need to reconcile all sorts of engine and platform differences to try and keep the racing competitive.

Edited by fioran0 on Thursday 12th February 17:34