918GT4 v. 991.2GT3 ....

[ChrisW.]

Is the difference really this big ?

[Twinfan]

Yep, standard 981 GT4 curve on the top by the look of it?

The new 4.0 fills in the holes...

Edited by Twinfan on Friday 2nd April 16:38

[ChrisW.]

Yes, standard 981 GT4 torque curve at the top and standard 991.2 GT3 curve at the bottom ... both from the car.

That's why I tuned my GT4 ... but Porsche certainly knew what they were doing when they specced the original GT4, even if it is the engine they continue to use in the 981 and 718 Clubsports ...

[Twinfan]

The new Clubsport engine is what I suspect the road car would have had if they could have made the right power and met emissions limits. I think they needed the extra CC for the 718 GT4 road car. I think yourself and TDT have the same mods on your cars i.e. Clubsport spec-ish?

The 991.2 GT3 engine is of course another step up

[ChrisW.]

My last GT3 was a 3.6 997 ... so this 4.0 991.2 is a real experience particularly with the GT3 version of the PDK which I first experienced on my Cayman R.

Yes the manual is very tactile, but I drove a very technical section of my favourite road this afternoon (without traffic) and the PDK is extremely effective and satisfying for that road !

[TDT]

ChrisW. said:

Is the difference really this big ?

Those in-car graphs bear only a passing resemblance to real life, and then each car is a little different. It’s just a representation.

If you look at the in-car graphs vs Porsches marketing dyno charts vs actual dyno chart, the torque plotting can look different also.

That said 991.2 GT cars have a dual resonance flap intake plenum, so it can optimise cylinder fill for both low revs with high velocity, but then openup at high revs for big volume for the big power.
This was one of the key engine advancements in the 991.2 GT3/RS over 991.1 GT
718 GT4 has its own version of a dual resonance intake plenum.
Multiple resonance flaps is something Porsche have used a lot over their history, probably most extremely in the X51 power kit for 9A1. This solution had 7 flaps in total.

981 GT4/Spyder and 991 GT3/RS have single flap intakes plenums.

This difference you see, where the torque seems to jump up on the 981, is representative of the cross over point when the flap opens.

If you know how, dual flap resonance GT intake plenum can be fitted into 9x1 cars which will offer a benefit there too, of optimised low end and big volume capacity at the top, right to redline .

In your case Chris your GT4 puts out similar peak torque to your 991.2 GT3(on paper figure) but the difference will be in how the GT3 carries that way up in the heavens at over 8.5k and allow you to rev out to 9k.

981 GT4/Spyder with some 718 CS components ends up looks very similar to 718 GT4 plot as posted by TwinFan, smoothed out torque and then power peaking higher than 718 GT4, but plots looking like a 35-40° diagonal from 0-8k RPM.

Edited by TDT on Friday 2nd April 20:00

[TDT]

Twinfan said:

The new Clubsport engine is what I suspect the road car would have had if they could have made the right power and met emissions limits. I think they needed the extra CC for the 718 GT4 road car.

I think this is probably right, it makes the power easily.
It’s about compliance with the new rules.

Also casuals wouldn’t have understood it, so 4.0 for marketing.

Edited by TDT on Friday 2nd April 19:13

[Cheib]

TDT said:

That said 991.2 GT cars have a dual resonance flap intake plenum, so it can optimise cylinder fill for both low revs with high velocity, but then openup at high revs for big volume for the big power.
This was one of the key engine advancements in the 991.2 GT3/RS over 991.1 GT

Edited by TDT on Friday 2nd April 19:07

Is that what causes the surge in power at around 6k rpm ?

[TDT]

Cheib said:

TDT said:

That said 991.2 GT cars have a dual resonance flap intake plenum, so it can optimise cylinder fill for both low revs with high velocity, but then openup at high revs for big volume for the big power.
This was one of the key engine advancements in the 991.2 GT3/RS over 991.1 GT

Edited by TDT on Friday 2nd April 19:07

Is that what causes the surge in power at around 6k rpm ?

If you’re referencing GT3, then likely yes. This will be a flap changeover point, and also changeover in the cams.
The flaps open and close singularly or in conjunction with each other throughout the rev range.
Complex to model.

Edited by TDT on Friday 2nd April 20:54

[ChrisW.]

Thanks Tyrone, Too technical for me but it sounds a likeable explanation.

The engine in the 991.2 GT3 is on other level to my tuned 981 ... it's like my GT4 completes it's real story at 7k and the 991.2GT3 adds another 2k to it ...

And our GT4 engines are in a different league to the standard "positioned" 981 GT4.

I can't talk for the 718 ...

There is no doubt that Porsche needed to tone the original GT4 down ... the £62k bargain ...

Edited by ChrisW. on Saturday 3rd April 08:53

[TDT]

Yep 991.2 GT3/RS unit is something special.
Will be added to the fleet at some point in the future.
I had a deal in November and maybe I should have taken it, but it was missing a few things that I really wanted, so decided to wait.
Hopefully 992 deliveries will see more coming back to market.