Jun 6, 2008 5:25:55 AM
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Ron (Houston)
- Rennteam Moderator
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- Loc: Houston, TX , United States
- Posts: 8812, Gallery
- Registered on: Apr 10, 2002
997 facelift more info
The engineers at Porsche AG are seizing upon the imminent introduction of the mid-life 997 911 Carrera and Carrera S coupe and cabriolet to evolve the company technology portfolio - and in big fashion. Beneath the always tentative minor tweaks to the exterior look of this sports car icon, the boffins have brought direct injection to the two Porsche 911 motors. Not only this, but they've updated and finally implemented their Porsche Doppel Kupplung twin-clutch transmission for major series production.
That Porsche introduced its direct injection first in the new 4.8-liter V8 of the Cayenne is no major surprise since doing so on a fairly traditional configuration was easier than for the oddball flat-sixes. But both the 3.6- and 3.8-liter are done at last and stratified direct injection once again results in more power and torque, greater fuel efficiency, and lower CO2 spewage. In this case as well, there are fewer individual components on the completely overhauled engines and the coinciding development of the PDK seven-speed transmission is bringing out the very best in either six-cylinder.
Regarding the direct injection itself, it is not a revolutionary spanking new approach, but applying it to a flat engine in a very confining engine bay is rather revolutionary. The injector for each cylinder sits in between the two intake valves and spurts fuel into the combustion chamber at up to 120 bar pressure depending on throttle load and current rev count. Below 3500 rpm and/or when the engine is cold, to avoid fuel losses, when the throttle is at or near the floor the injectors are ordered into tiny multi-spurt mode during only the intake stroke until things heat up sufficiently to guarantee a complete burn of a fuller spurt. Combustion in this case happens very late to help build heat quickly. Through all of this, the new shape of the piston crowns feeds the fuel swirled directly into the chamber directly toward the optimal points near the spark plugs. There is a slightly different idle sound happening now, as is to be expected with a new efficient burn.
Both engines in this development process have taken on modified dimensions to the combustion cylinder, ending up with 3614cc for the 3.6 (was 3596cc) and 3800cc for the 3.8 (was 3824cc). Bore and stroke measurements for the 3.6-liter motor have changed from the former 96 x 82.8mm to 97 x 81.5mm, while the 3.8-liter goes from 99 x 82.8mm to a very altered 102 x 77.5mm. What these modifications reflect chiefly is the desire for a faster revving experience, and redline moves up to 7500 rpm on both powerplants from the former 7300-rpm ceiling.
Besides the new combustion chamber dimensions, there is an updated crankshaft, a new set of oil and water pumps, and the entire intake area has naturally been redesigned as no more pre-mixing of air and fuel needs to happen in the "waiting room" outside the chambers. The fresh crankshaft is used mainly due to the newly engineered crankcase. In the previous port-injected engines, the crankcase was a four-piece unit and the crankshaft mounted in a separate bearing housing. Now, we get a two-piece crankcase with fully integrated crankshaft bearings.
Meantime back at the sparking end of the cylinders, we now have one-piece cylinder heads with integrated camshaft bearings plus new guide cylinders for the hydraulic cup tappets. This scheme strips away some weight while adding mechanical stability, as lower operating friction was a priority. As well, new profiles for the intake and exhaust camshafts help enhance engine responsiveness and overall economy while keeping things smooth at the highest engine speeds. The formerly necessary intermediate shaft to help drive the timing chains and assist reduction of the loads on the camshaft drive has been eliminated, since there are new highly resistant timing chains now used to handle the stresses imposed upon them.
Diameter on the shift tappets has now been reduced from 33 millimeters to 31 mm and tappet size on the exhaust valves comes down also, from 33 mm to just 28 mm. This is key in lowering mass inertia as well as facilitating the new higher revs required of the whole machine. In an ingenious touch, an additional coolant element has been designed into the very seat ring of the outlet valves to help markedly in keeping the cylinder heads cooler.
The thermal and mechanical stability of the new motors has been upgraded by switching from a former "open-deck" interface for the cylinder liners and their gaskets. The new closed-deck scheme ensures the cylinder liners are no longer freely exposed around the cylinder head gaskets, now opting to actually connect them with the housing via a top plate which also comprises the coolant sleeves. This ensures, again, greater stability in the cylinder shape and design, while promising less oil consumption, and the always desirable lower mechanical friction.
Thermal efficiency, air flow, and 20 percent improved coolant management are now so good on either flat-six that the traditional center pancake radiator up front has also been eliminated. In this less-friction-with-fewer-components design both engines can also boast an overall weight that is 13.2 pounds less than the engines they replace.
Beneath the working part of each engine, a new baffle plate separates the crank case and sump to thereby reduce splash losses and oil foaming. The dry-sump management has been updated as well with two suction pumps per cylinder head sending the oil back to the sump. A new fifth electronically operated on-demand compressed oil pump is driven off of the new crankshaft via a chain, and this constantly changes the amounts of oil that get sent downstream as needed by the use of a hydraulically operated gear that moves in an axial direction, changing the amount of mesh depending on the amount of oil needed. One more physical nuance is the main coolant pump now sitting outside of the crankcase to facilitate access to it for repair or upgrading.
The port-injected engines (which will continue being built for the rest of the 911 lineup that still needs them) have for a long time used a single chamber air filter system with an integrated intake funnel. For the new DI units, the air filter system now takes on a double-chamber design with two intake openings and separate intake funnels on the car's rear engine lid. The old flat pancake filter now alters to two round air filters with a longer service life.
The 3.8-liter flat-six does still get special treatment with its actively switchable resonance volume function in the upper section of the filter housing which causes greater air flow and better engine sound when engine speeds and heat are high. The new manifold now has more resonance chambers, while the resonance pipe and distributor pipe are now integrated as one component between the right and left distributors. A good reason for this freshened design is additional torque at lower engine speeds. Between 2600 and 5100 rpm, the resonance butterfly on the 3.8-liter remains closed to not anger the villagers, but beyond 5100 rpm the sound booms in a new note that shows that Porsche has finally paid some mind to our constant laments regarding the asthmatic 911 rasp.
Power ratings tell no lies either. The 3.6-liter flat-six without all of these modifications rates SAE 321hp at 6800 rpm, while the new DI version reads 341hp at 6500 rpm. The bigger 3.8 goes from 350hp at 6600 rpm to now putting out 380hp at 6500 rpm. Torque measurements meanwhile improve as well, the 3.6 upping from 273lb-ft at 4250 rpm to 287lb-ft at 4400 rpm, while the 3.8 moves up from 295lb-ft at 4600 rpm to 310lb-ft at 4400 rpm. At its quickest, according to company estimates, the 911 Carrera S with the seven-speed PDK box and Sports Chrono Plus option can accelerate to 62mph now in just 4.3 seconds. The base Carrera with manual Getrag six even gets there now in just 4.9 seconds - not bad for the slowest member of the hardtop family.
And, all the while, of course fuel mileage improves and CO2 emissions drop. For the 3.6-liter in the Carrera, fuel consumption on the cabriolet body with PDK (versus the outgoing Daimler five-speed Tiptronic S) drops by up to 13.2 percent, carbon dioxide levels dropping likewise by 14.7 percent. For the 3.8 in the Carrera S, the coupe with PDK lowers consumption by up to 12.8 percent, CO2 emissions dropping in similar fashion to the 3.6.
That Porsche introduced its direct injection first in the new 4.8-liter V8 of the Cayenne is no major surprise since doing so on a fairly traditional configuration was easier than for the oddball flat-sixes. But both the 3.6- and 3.8-liter are done at last and stratified direct injection once again results in more power and torque, greater fuel efficiency, and lower CO2 spewage. In this case as well, there are fewer individual components on the completely overhauled engines and the coinciding development of the PDK seven-speed transmission is bringing out the very best in either six-cylinder.
Regarding the direct injection itself, it is not a revolutionary spanking new approach, but applying it to a flat engine in a very confining engine bay is rather revolutionary. The injector for each cylinder sits in between the two intake valves and spurts fuel into the combustion chamber at up to 120 bar pressure depending on throttle load and current rev count. Below 3500 rpm and/or when the engine is cold, to avoid fuel losses, when the throttle is at or near the floor the injectors are ordered into tiny multi-spurt mode during only the intake stroke until things heat up sufficiently to guarantee a complete burn of a fuller spurt. Combustion in this case happens very late to help build heat quickly. Through all of this, the new shape of the piston crowns feeds the fuel swirled directly into the chamber directly toward the optimal points near the spark plugs. There is a slightly different idle sound happening now, as is to be expected with a new efficient burn.
Both engines in this development process have taken on modified dimensions to the combustion cylinder, ending up with 3614cc for the 3.6 (was 3596cc) and 3800cc for the 3.8 (was 3824cc). Bore and stroke measurements for the 3.6-liter motor have changed from the former 96 x 82.8mm to 97 x 81.5mm, while the 3.8-liter goes from 99 x 82.8mm to a very altered 102 x 77.5mm. What these modifications reflect chiefly is the desire for a faster revving experience, and redline moves up to 7500 rpm on both powerplants from the former 7300-rpm ceiling.
Besides the new combustion chamber dimensions, there is an updated crankshaft, a new set of oil and water pumps, and the entire intake area has naturally been redesigned as no more pre-mixing of air and fuel needs to happen in the "waiting room" outside the chambers. The fresh crankshaft is used mainly due to the newly engineered crankcase. In the previous port-injected engines, the crankcase was a four-piece unit and the crankshaft mounted in a separate bearing housing. Now, we get a two-piece crankcase with fully integrated crankshaft bearings.
Meantime back at the sparking end of the cylinders, we now have one-piece cylinder heads with integrated camshaft bearings plus new guide cylinders for the hydraulic cup tappets. This scheme strips away some weight while adding mechanical stability, as lower operating friction was a priority. As well, new profiles for the intake and exhaust camshafts help enhance engine responsiveness and overall economy while keeping things smooth at the highest engine speeds. The formerly necessary intermediate shaft to help drive the timing chains and assist reduction of the loads on the camshaft drive has been eliminated, since there are new highly resistant timing chains now used to handle the stresses imposed upon them.
Diameter on the shift tappets has now been reduced from 33 millimeters to 31 mm and tappet size on the exhaust valves comes down also, from 33 mm to just 28 mm. This is key in lowering mass inertia as well as facilitating the new higher revs required of the whole machine. In an ingenious touch, an additional coolant element has been designed into the very seat ring of the outlet valves to help markedly in keeping the cylinder heads cooler.
The thermal and mechanical stability of the new motors has been upgraded by switching from a former "open-deck" interface for the cylinder liners and their gaskets. The new closed-deck scheme ensures the cylinder liners are no longer freely exposed around the cylinder head gaskets, now opting to actually connect them with the housing via a top plate which also comprises the coolant sleeves. This ensures, again, greater stability in the cylinder shape and design, while promising less oil consumption, and the always desirable lower mechanical friction.
Thermal efficiency, air flow, and 20 percent improved coolant management are now so good on either flat-six that the traditional center pancake radiator up front has also been eliminated. In this less-friction-with-fewer-components design both engines can also boast an overall weight that is 13.2 pounds less than the engines they replace.
Beneath the working part of each engine, a new baffle plate separates the crank case and sump to thereby reduce splash losses and oil foaming. The dry-sump management has been updated as well with two suction pumps per cylinder head sending the oil back to the sump. A new fifth electronically operated on-demand compressed oil pump is driven off of the new crankshaft via a chain, and this constantly changes the amounts of oil that get sent downstream as needed by the use of a hydraulically operated gear that moves in an axial direction, changing the amount of mesh depending on the amount of oil needed. One more physical nuance is the main coolant pump now sitting outside of the crankcase to facilitate access to it for repair or upgrading.
The port-injected engines (which will continue being built for the rest of the 911 lineup that still needs them) have for a long time used a single chamber air filter system with an integrated intake funnel. For the new DI units, the air filter system now takes on a double-chamber design with two intake openings and separate intake funnels on the car's rear engine lid. The old flat pancake filter now alters to two round air filters with a longer service life.
The 3.8-liter flat-six does still get special treatment with its actively switchable resonance volume function in the upper section of the filter housing which causes greater air flow and better engine sound when engine speeds and heat are high. The new manifold now has more resonance chambers, while the resonance pipe and distributor pipe are now integrated as one component between the right and left distributors. A good reason for this freshened design is additional torque at lower engine speeds. Between 2600 and 5100 rpm, the resonance butterfly on the 3.8-liter remains closed to not anger the villagers, but beyond 5100 rpm the sound booms in a new note that shows that Porsche has finally paid some mind to our constant laments regarding the asthmatic 911 rasp.
Power ratings tell no lies either. The 3.6-liter flat-six without all of these modifications rates SAE 321hp at 6800 rpm, while the new DI version reads 341hp at 6500 rpm. The bigger 3.8 goes from 350hp at 6600 rpm to now putting out 380hp at 6500 rpm. Torque measurements meanwhile improve as well, the 3.6 upping from 273lb-ft at 4250 rpm to 287lb-ft at 4400 rpm, while the 3.8 moves up from 295lb-ft at 4600 rpm to 310lb-ft at 4400 rpm. At its quickest, according to company estimates, the 911 Carrera S with the seven-speed PDK box and Sports Chrono Plus option can accelerate to 62mph now in just 4.3 seconds. The base Carrera with manual Getrag six even gets there now in just 4.9 seconds - not bad for the slowest member of the hardtop family.
And, all the while, of course fuel mileage improves and CO2 emissions drop. For the 3.6-liter in the Carrera, fuel consumption on the cabriolet body with PDK (versus the outgoing Daimler five-speed Tiptronic S) drops by up to 13.2 percent, carbon dioxide levels dropping likewise by 14.7 percent. For the 3.8 in the Carrera S, the coupe with PDK lowers consumption by up to 12.8 percent, CO2 emissions dropping in similar fashion to the 3.6.
not now not ever 
