• Nov 13, 2007
Squeezing 480 HP from a 3.6L flat-six is an impressive feat, and the latest 911 Turbo does it with a level of sophistication, refinement, and reliability that would have been thought impossible just a few years ago. Everything is relative, though, and "more" is always the operative word when it comes to Porsche's GT2. So, how does one squeeze fifty additional ponies from an such a powerplant? Considering all the different challenges - emissions, durability, drivability, and fuel economy - it's certainly not an easy task. Fortunately, Porsche has no small amount of experience squeezing more power from turbocharged boxers, and that knowledge was put to good use on the new 2008 GT2.

Live Photos Copyright ©2007 Eric Bryant / Weblogs, Inc.



Porsche's latest turbocharged engines are a far cry from the automaker's forced-induction offerings from two decades ago. Modern engine management systems tamed the lightswitch-like power delivery, and now the use of variable camshaft phasing and variable-vane turbocharger technology has resulted in a powerband that's flatter and fatter than that of larger naturally-aspirated motors.



The GT2 uses a pair of BorgWarner/KKK turbochargers that are similar to those employed on the Turbo, but with a slightly larger compressor and some flow optimization applied to the turbine side. Additionally, the ECU allows a bit more boost, and the result is an astonishing 505 lb-ft from 2200 to 4500 RPM. Even after the peak is reached, plenty of thrust remains through the next 2000 RPM up to the horsepower peak of 530 at 6500 RPM. To the driver, this means that enormous power is on tap basically anywhere between idle and redline. Gear selection can be treated as an afterthought with minimum penalty, which is a useful attribute when there are several other decisions to be made on the racetrack or street.



Visible in the shot above is the tangle of oil lines that's required to operate the variable vanes on the turbo's turbine side. Expect future generations of this technology to utilize direct-mounted electrical actuators, but temperature in this area remains troublesome - as it is, miraculously tight tolerances and careful management of thermal expansion is required to make VVT technology work with the hotter exhaust temps of spark-ignition engines.



The management of induction tract resonances is critical to maximizing the power of naturally-aspirated engines, but the turbocharged engines have typically foregone this technique in favor of adding additional manifold pressure (resonances in a pressurized manifold are also extremely tricky to tame). Cranking up the boost has a drawback, however, in the form of additional heat, and so more fuel and less timing is required to maintain acceptable durability.



Porsche claims to have countered this with an "expansion-type" manifold that makes use of the typically-unused oscillations that are still present in a forced-induction manifold. A longer and smaller-diameter primary tract is combined with more plenum volume and shorter individual cylinder runners to yield a cooler intake charge for a given flow rate, which means that the fuel mixture can be leaned and more ignition timing can be utilized. Both changes improve fuel economy and dump less heat into the exhaust system - undoubtedly a win-win scenario. Amazingly enough, it all fits in the restrictive rear engine compartment of the 911, and we expect to see this on future forced-induction engines from Porsche.



The use of titanium components for the exhaust system frees up several pounds, and while Porsche doesn't credit it with any improvement in power, we like it just for the enhanced sonic qualities. For those viewing the tail end of the GT2 - that'd be most observers - a set of polished tips poke through the rear valance.



Routing all 530 HP to the six-speed transaxle requires a heavy-duty clutch, but balancing torque transmission with pedal effort and durability requires some fancy engineering. Additionally, it's desirable to keep mass and diameter to a minimum to avoid creating too much inertia (ground clearance also becomes an issue with low-riding sports cars). A twin-disc clutch from Sachs is used here; doubling the number of discs increases the torque capacity accordingly without an increase in pressure plate force. The GT2's clutch pedal is still heavier than most, but it's manageable. We'd still recommend some time at the gym before getting stuck in rush-hour traffic.



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  • 13 Comments
      • 7 Years Ago
      I think the engineers design a great engine, very interesting power plant package. Porsche's 911 GT2 display-cutaway engine model looks complex/amazing.

      Porsche's 2008 911 GT2 engine advancement technologies...I think the engine looks very compact but packs a lot of power. I like the twin turbo setup...(I think newer garret turbochargers could produce even more horsepower).

      I also like the twin disc high performance racing clutch and strong lightweight flywheel. The top and bottom high rev camshaft lobes/layout are interesting to match with and allow clearance for the turbochargers. The oil lines, fat-cat titanium exhaust system and etc looks well designed too...)

      Hmmm...interesting, with that much power, I wonder if the engine has adequate cooling capacity-overheating? Overall, interesting article on engine advancements.
      • 7 Years Ago
      I am not an engineer, but in comment to the posts about the "smashed pipe" on the cool side. If it is true that one of the problems of long routes to intercoolers (eg subaru front mount) is a loss of intake velocity. I would think the same can be said for too large or long a pipe.

      Scenario: if I have a very long fat hose on my shop vac it seems to work just as well as with a short skinny one(with the same nozzle), however if I turn it on suddenly there seems to be a longer delay untill it is a peak vacuum.

      While I am sure the shape of the pipe is a packaging compromise I wonder if having a smaller internal volume makes it act like a shorter pipe. Correct me if I am wrong, but I would guess there is still a MAF on the other end of that pipe. I would think having the smallest drop in vacuum through that length would allow for faster response and more accurate flow readings.

      I started thinking there must be a good reason because Madgamer is right, Porsche engineers are not stupid...
        • 7 Years Ago
        It is all due to packaging concerns. It is not ideal to have many bends or intrusions in piping geometry. It is also not ideal to have long pipe length. The Porsche's engine bay does not leave many options for the placement of the turbochargers so they had to work with what they were given.

        The charge piping on the BMW 335i also does a pancake job to meet packaging constraints.
      • 7 Years Ago
      What is the large silver box in line with the flywheel on the passenger side in this picture?

      http://www.autoblog.com/photos/2008-porsche-gt2-intro/482032/full/

      Is it a localized cooling reservior for the turbos and/or other fluids? It could be an external sump, but its vertical orientation seems to preclude that possibility.
        • 7 Years Ago
        That's the oil tank of the dry sump system. The vertical orientation minimizes sloshing around under cornering forces.
      • 7 Years Ago
      Very cool article, thanks for posting it!

      It is interesting to see the oil lines running to / from the turbo for the variable vanes in the turbine. I guess I never really thought about how those would be actuated!

      It also looks like the turbo has it's own little oil sump? I wonder what the purpose of that is? In most turbo cars the oils drains back into the pan just as fast as it's pumped into the turbo.

      BTW, that is such a cool job someone has to create these cutaway engine displays!
        • 7 Years Ago
        The turbochargers have their own oil sump mostly because of where they are mounted. On many turbocharger configurations oil drains back to the engine oil pan via gravity. However if the turbocharger drain is below the oil pan level gravity will not move the oil and it will just pool in the turbo bearing housings. Since Porsche mounted the turbos at a low point the oil needs a sump and a pump to move it back to the pan.
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