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Discussion Starter · #1 · (Edited)
B6 3.0 991.2 Carrera

Horsepower: 370
Torque: 332 lb-ft
Boost Pressure: 13.1 psi
Bore x Stroke: 91mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 10.0:1
Intercooler: Air to Air
Turbos (2): 49mm compressor/45mm turbine

B6 3.0 991.2 Carrera S

Horsepower: 420
Torque: 369 lb-ft
Boost Pressure: 16.0 psi
Bore x Stroke: 91mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 10.0:1
Intercooler: Air to Air
Turbos (2): 51mm compressor/45mm turbine

B6 3.0 991.2 Carrera GTS

Horsepower: 450
Torque: 405 lb-ft
Boost Pressure: 18.0 psi
Bore x Stroke: 91mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 10.0:1
Intercooler: Air to Air
Turbos (2): 55mm compressor/48mm turbine

B4 2.5 982 718 Boxster/Cayman S

Horsepower: 350
Torque: 309 lb-ft
Boost Pressure: 14.5 psi
Bore x Stroke: 102mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 9.5:1
Intercooler: Air to Water
Turbo (1): VTG 64mm compressor/55mm turbine

source (991.2) PorscheBoost - Comparing Porsche 991.2 Carrera, S, and GTS 3.0 9A2 engine output and turbocharger sizes
source (982) https://www.motoring.com.au/porsche-working-on-more-boxer-fours-101482/
I could not establish turbo size for the B4 2.0, if someone has that info, kindly fill-in.

Analysis*: All these engines have essentially the same internals, B4 basically being two-thirds of the B6 (longitudinally). Incremental power increases throughout the 3.0 Carrera line are achieved solely with larger turbos and tuning. By contrast, the bored-out B4 runs lower compression and has air-to-water intercooling; but its main difference is having one quite larger VTG turbo with more flow capacity than either of the B6's twin conventional turbos.

Now, that single VTG feeds all 2.5 litres of swept-area in the B4, versus 1.5 litres in each bank of the B6 for its smaller twin turbos. That seems like an advantage for the twin configuration, but I think a simple formula like turbo count*compressor-size/swept-area misses something about the physics of squeezing air molecules. Something that, crucially, can make one big turbo more powerful than two smaller ones. Because at peak power the big turbo's larger internal volume means air molecules are squeezed down less for the same flow; equals less heat generated in the compressed stream flowing out of the turbo. Therefore a cooler, denser charge for a given level of boost; more oxygen/fuel drawn into the cylinders on intake; more power. Of course you need variable vane geometry allowing the larger VTG to spool-up like a smaller turbo for reduced lag -- that, not ultimate power, was the historical advantage and motivation driving twin turbo set-ups pre-VTG (along with packaging and cooling considerations).

I think this single-but-large-VTG turbo effect helps explain the 718 S ability to 'run above' hp rating and power/weight calculations.

*this is my best -- but entirely non-engineer-reviewed -- analysis based on reading everything I can find online (which is not all that much!) on VTG and engineering aspects of twin-turbos versus one larger VTG (or twin-scroll) turbo. If you have corrections or addtl. insights, please contribute to this thread.
 

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The 718 Boxster may not have the most power on paper, but it certainly has a lot of on road personality and that's what counts towards something you take onto and off city roads.
 

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Discussion Starter · #4 ·
Updated this chart to include 718 GTS data (from the just-published C&D First Drive, link below). Of note: unlike earlier GTS previews, the C&D piece identifies a new, larger VTG turbo (with 67mm compressor wheel) as part of the GTS spec. I think this opens up the possibility of Porsche offering a factory X51 power kit to upgrade S engine to GTS power (similar to Carrera X51 kit, see PorscheBoost link below).

B6 3.0 991.2 Carrera

Horsepower: 370
Torque: 332 lb-ft
Boost Pressure: 13.1 psi
Bore x Stroke: 91mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 10.0:1
Intercooler: Air to Air
Turbos (2): 49mm compressor/45mm turbine

B6 3.0 991.2 Carrera S

Horsepower: 420
Torque: 369 lb-ft
Boost Pressure: 16.0 psi
Bore x Stroke: 91mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 10.0:1
Intercooler: Air to Air
Turbos (2): 51mm compressor/45mm turbine

B6 3.0 991.2 Carrera GTS

Horsepower: 450
Torque: 405 lb-ft
Boost Pressure: 18.0 psi
Bore x Stroke: 91mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 10.0:1
Intercooler: Air to Air
Turbos (2): 55mm compressor/48mm turbine

B4 2.5 982 718 Boxster/Cayman S

Horsepower: 350
Torque: 309 lb-ft
Boost Pressure: 16.7 psi
Bore x Stroke: 102mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 9.5:1
Intercooler: Air to Water
Turbo (1): VTG 64mm compressor/55mm turbine

B4 2.5 982 718 Boxster/Cayman GTS

Horsepower: 365
Torque: 317 lb-ft
Boost Pressure: 18.1 psi
Bore x Stroke: 102mm x 76.4mm
Redline: 7500 rpm
Compression Ratio: 9.5:1
Intercooler: Air to Water
Turbo (1): VTG 67mm compressor/55mm turbine

source (991.2) PorscheBoost - PorscheBoost - Comparing Porsche 991.2 Carrera, S, and GTS 3.0 9A2 engine output and turbocharger sizes
source (982) https://www.motoring.com.au/porsche-working-on-more-boxer-fours-101482/
source (982 GTS): https://www.caranddriver.com/reviews/2018-porsche-718-boxster-cayman-gts-first-drive-review
I could not establish turbo size for the B4 2.0, if someone has that info, kindly fill-in.
 

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ZuffenHouseRule, Thank you again and again for your constant efforts to bring more and more info to this forum and for sharing your knowledge.

I am impressed at the fact that the 718 GTS comes with a 67mm compressor (vs twin 49mm for the 911 C). I wonder at what RPM these turbos spin. It must be insane. Do the smaller ones spin faster?

Do any of these numbers tell us which turbo is under the least and the most stress ( the big ones or the twin smaller ones)? Would this be pertinent when we wonder which one may last longer?
 

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From what I have found, which isn’t much, the 2.0t turbo is a variant of the K04. Hopefully is similar to the IHI38 in the golf R. They are good for up to 400whp in the R 2.0.
 

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From what I have found, which isn’t much, the 2.0t turbo is a variant of the K04. Hopefully is similar to the IHI38 in the golf R. They are good for up to 400whp in the R 2.0.
interesting. I hope so, I’ve been debating if I should start mods or just wait it out a bit before jumping up to a GTS.
 
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