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GM’s First V-6 Direct Injection Engine

Illustration of the V-6 VVT DI. Click to enlarge.

GM announced that it will make the 3.6L V-6 gasoline engine with direct injection (DI) and variable valve timing (VVT) technologies the standard engine in the 2008 Cadillac STS.

With direct injection, less fuel is required to produce the equivalent horsepower, especially at normal cruising speeds, compared to a conventional port-injection combustion system. The technology can be used to support downsizing engine applications for bigger benefits in fuel consumption, or, as in this case, to deliver more power with incremental benefits in fuel consumption.

The new standard engine for STS delivers 302 horsepower (225 kW) at 6,300 rpm (+18%) and torque of 272 lb-ft (366 Nm) at 5,200 rpm (+8%).  At the same time, the engine is expected to deliver improved fuel efficiency. Official EPA fuel economy statistics for the 2008 model have not yet been announced. On the outgoing 2007 model STS, EPA fuel economy is 18 mpg city and 27 mpg hwy.

Our goal was to deliver an engine with outstanding power and improved efficiency...It’s the latest example of our strategy to continue to reduce emissions and improve fuel economy without sacrificing performance.

—Tim Cyrus, chief engineer for high-feature V-6 and Northstar V-8 engines

The 3.6L V-6 engine is GM’s third engine variant offered with direct injection technology. GM offers an Ecotec 2.0-liter four-cylinder Turbo engine with direct injection on the 2007 Saturn Sky Red Line and Pontiac Solstice GXP roadsters. Since 2004, Opel has offered a naturally aspirated Ecotec 2.2-liter direct injection engine in Europe.

By the end of 2008, GM forecasts it will produce as many as 200,000 vehicles globally with direct injection technology, and projects that by 2010, one of every six GM vehicles in North America will be equipped with a direct injection engine.

With direct injection technology, fuel is sprayed directly into the engine cylinder where it is mixed with air. As the fuel vaporizes in the cylinder, the air and fuel mixture is cooled. This enables the use of a higher compression ratio in the combustion chamber, 11.3:1, which improves engine performance and efficiency.

On cold starts, direct injection can be controlled to create a richer air/fuel mixture around the spark plug, making it easier to ignite in a cold engine. This results in a smoother operation and an approximate 25% reduction in cold-start hydrocarbon emissions during the cold-start and warm-up.

Direct injection requires higher fuel pressure than conventional fuel-injected engines, and the engine-driven high-pressure fuel pump is used to supply up to 1,740 psi (120 bar) of pressure. The system regulates lower fuel pressure at idle—approximately 508 psi (35 bar) and higher pressure at wide-open throttle. The exhaust cam-driven high-pressure pump works in conjunction with a conventional fuel tank-mounted supply pump.

The 3.6-liter V-6 also features the US automotive industry’s first isolated fuel-injector system. This helps reduce the overall engine noise.

In addition to direct injection, variable valve timing (VVT) also helps reduce exhaust emissions and improve performance and fuel economy by optimizing the phasing of the intake and exhaust valves relative to the crankshaft position at all operating conditions.

The result is linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (maximum horsepower per liter of displacement) without sacrificing overall engine response and driveability.

Cam phasing helps reduce exhaust emissions by optimizing exhaust valve overlap and eliminating the need for a separate exhaust gas recirculation (EGR) system.

By closing the exhaust valves late at appropriate times, the cam phasers allow the engine to draw the desired amount of exhaust gas back into the combustion chamber, reducing unburned hydrocarbon emissions.

The return of exhaust gases also decreases peak temperatures, which contributes to the reduction of oxides of nitrogen (NOx) emissions. In tandem with the 25% reduction in cold-start hydrocarbon emissions enabled by direct injection, the 3.6-liter VVT DI V-6 surpasses all emissions mandates, and does so without emissions control systems such as EGR and air injection reaction (AIR).



Good to see GM near the forefront of technology in production for a change. It should push hard to introduce DI across its product lines, especially since it isn't eager to introduce diesels to America. A 2.0L I-4 in a similar state of tune would deliver 167 HP.


Here is the GM problem in a nutshell!!

They could have created an engine with significantly better fuel consumption, but instead went for more power, but remember it would cost $6000 to improve fuel consumption as required by CAFE.

Would it really kill them to do both, after all they are the second largest auto maker in the world, a more power variant and a better fuel economy variant, offer both in the STS and other models, and see what sells!

They are just so frustrating


Could you not do both by remapping the engine in s/w ?


GM long ago figured out what sells - power - particularly in a premium line like Cadillac. It would have been easier for them to make the engine more powerful *without* improving the efficiency, so why not appreciate this for the good thing it is?


Anybody else would have kept the same power and reduced the size of the engine's footprint. Maybe it costs too much to downsize the engine. Detroit is frustrating, alright. They can watch as they shoot themselves in the foot and then, keep shooting. They'd do better spending their energies and money developing a plug-in. They already let Japan get a ten year headstart on hybrids.
The world's passing them by and they still have their heads in the sand. If I were the government, I wouldn't bail them out either. They'd waste the money on the wrong project and go out of business anyway. Sad. You can't blame the workers and the unions for GM having the wrong mindset. They just build what they are told to.


Remapping might save a little, but to really see a economy gain at the same power GM would have to downsize the engine to about 3.0L. The VVT is tuned one way at the factory so the opportunity for on-the-fly engine remapping gains may be limited. Having sport/econ modes programmed in the transmission and available via a console button would probably do more than engine remapping.

Rafael Seidl

Direct injection is already fairly common in Europe and I expect, in Japan as well. It's important to realize that GDI is not a single technology but rather a field, with large differences in how it is implemented.

First-generation systems use special piston shapes and/or charge motion to deliver an ignitable air-fuel mixture at the spark plug at the right time. The injector tip usually lies near the intake valves and close to the head gasket. Injection pressures are moderate and injection events early relative to ignition. Pioneered by Mitsubishi, this approach failed to live up to its hype because the fraction of the engine map in which stratified combustion is feasible is quite small. Moreover, tightening emissions standards everywhere mean that stratified combustion now requires an expensive NOx aftertreatment system. Those are typically quite sensitive to sulfur in the fuel.

For these reasons, VW/Audi switched from Fuel Stratified Injection (FSI) to homogenous GDI, mostly by increasing injection pressures. They kept the FSI moniker but cannot currently deliver the full potential of GDI.

Mercedes and BMW have both introduced engines feature second-generation spray-guided GDI. In this, the tip of the piezo injector is located centrally in-between the four valves and close to the spark plug. Injection pressures are high (up to 200 bar) and the final injection event (there are typically 2-3) occurs just prior to ignition. The fluid dynamics of the conical spray pattern produce a toroidal vortex of ignitable air-fuel mixture in the immediate vicinity of the spark plug.

Spray-guided GDI permits fuel stratification even at the power levels required to maintain cruising speeds of up to 100mph. In the European NEDC cycle, these systems deliver 10-12% improvement in average fuel economy. However, the combination of expensive injectors, tight manufacturing tolerances and the overhead of an NOx store catalyst make the approach very expensive.

My guess is the GM system described above is a first-generation homogenous GDI implementation. This is very compatible with not just VVT but also turbocharging, because of improved scavenging in part load. Of course, a 2.4L V6 with a single twin-scroll turbo would match the rated power of a 3.6L naturally aspirated unit, with even better fuel economy and acceptable turbo lag (<0.2s).


Agreed, the fact that GM is leading the way in GDI (any advanced ICE technology for that matter) in the US market is a refreshing trend. For a vehicle of this class/size I would personally prefer a smaller (LIGHTER) I-6 2.5 VG turbo GDI with slightly less power but w/a much-improved torque curve. The weight savings of an I-6 over a V6 alone would be large enough to allow for significant weight reduction throughout the entire vehicle. Picture what the above power/torque could do in a 3000lbs CTS. I, for one, would like to see auto manufacturers start reveresing the trend of heavier and heavier vehicles.


"Anybody else would have kept the same power and reduced the size of the engine's footprint."

Wrong. Show me ANY car manufacturer that kept power the same across a model re-design and I'll eat my hat. Check out the specs for the 2005 and 2007 Camry, or Hyundai Sonata, or the last version of the Accord relative to the current model. I have NEVER seen power stay the same, it always goes up, at least a small amount, engine redesigns always push power up higher.



"They could have created an engine with significantly better fuel consumption, but instead went for more power"

I think you guys are being a little hard on GM here. This engine will likely entice many more STS buyers to go for the V6 instead of the V8. The STS is a 4000lb+ car. If they went with a smaller engine, you'd wind up with more people opting for the V8.


GM does make a 2.8 liter high-content V6,as well as a 3.2, of the same engine family. It's used in Asia, Europe, etc.

The horsepower race prpbably precluded them from using it here for now, but if CAFE or market demand called for it, its there.

Angelo is right; probably (hopefully) more buyers will chose the V6 in the STS than the V8.

Stan Peterson

What a tough crowd.

A decade go, GM ballyhooed the NorthStar V8 as its premium engine. It sported a Small downsized, aluminum block DOHC, 32 Valve design and after a redesign to eliminate seal leakage it went VVT a few years ago. GDI will soon follow. In effect it obsoleted all its old V8 families. The SFC of the Northstar is fine.

GM's V6 lines were pretty prosaic. A cheap V6 starting with OHV 12 valve, iron block 2.8 liter designed for the entry range X-cars (Citation etc), and an antique chopped iron block Buick OHV V8 reduced to a OHV V6 produced by Buick, the 3.8 liter. This was done in the response to the original downsizing efforts in the 1960s-1980s.

The 3.6 liter Shortstar V-6 is a high technology replacement for those engine families and sports DOHC 24 valve, aluminum block, VVT and GDI. Many V8s will not be installed, and the start of the phaseout of the OHV 12 valve 3800 is ongoing.

The SFC of the 3.6 is much better than either of those designs and compares to any ICE V6s in the world, including those from the best of the Japanese or the the Germans.

GM also has a a cheap I4 and a high tech I4 in the Ecotec-4; which is all alloy DOHC, 16 valve, engine that awaits general adoption of the VVT and GDI technology.

In short GM's engine technology now will match any in the world. You should be celebrating; instead all I hear is derision.

A little refinement work on the Ecotec-4 to add GDI and Atkinson cam phasing, together with the GM/DCX/BMW dual mode hybrid transmission, and you have the basis for a wonderful state of the art HEV/PHEV compact drive trains. Ditto with the 3.6 V-6 for larger vehicle HEV/PHEVs applications.

By comparison, DCX is only now only funding the factories to build a V6 family called the Phoenix V-6 a line to match the GM 3.6 technologies in in 2010 or 2011. Although DCX does already have a fully modern I-4 World engine; an alloy, DOHC 16 valve design with VVT, it only introduced last year. It's V8s are crude (Hemi for truck) or under-developed (4.7) by comparison to the Northstar.

DCX might have had a lucky break; V-8s may not be needed for long. With the coming of HEVs/PHEVs, even DCX will have the basis for very good such drive trains based on their World I-4 (or Phoenix V-6s) mated to a dual mode hybrid transmission.

Come on guys, celebrate. You can see the outlines of the future coming as another major chunk of technology and factory infra-structure to build it, is laid in place.


Imagine what the 275bhp + 300ft-lbs from a 2.5 I-6 GDI VG Turbo could do in a 3000 lbs CTS.

I, for one, would like to see auto manufacturers start reversing the trend of heavier and heavier vehicles.

A 20% weight reduction across all vehicle ranges would be a welcome start. This would be attainable through the implementation of small (right-sized) GDI turbo alloy engines with polymer body panels (as seen in 335iC and older Saturns), extensive use of aluminum (Jaguars & NC Miata), composites (see newest M3's roof- & any number of "ricers"), not to mention: friction stir welding, hydroforming, adhesive bonding, rivets, etc.

Even without any further advances in ICE or battery technology there are numerous ways to lighten their vehicles so that GM could improve on their CAFE ratings. Additionally, they won't cost over $6,000 per vehicle as Lutz claims!

Stan Peterson


I have to make an apology. The moniker "Shortstar" does not apply to the new DOHC 60degree 24 valve all alloy premium v6 line of which the above 3.6 liter v6 is a member. The line was is called simply the High Feature V6 family, and is availble in 2.8 and 3.2 and 3.6 liter versions of the same engine with the two smaller versions availble outside the USA.


The automakers say they can't meet the proposed CAFE standards now in congress. This announcement shows why. Something needs to be done to stop this performance race. While congress is at it, they should cap or at least seriously penalize horsepower.


There's just no pleasing some people.

Angelo rightly points out that this engine will likely keep many buyers from considering the V8 option. GM has produced a V6 engine with more horsepower, more torque, lower overall emissions, and greater fuel efficiency.

I thought this was the kind of engine downsizing that some people here wanted to see. There's no reason why we can't have both high performance and high efficiency.

This is luxury car, not an econobox. If you want this technology to show up in smaller, less expensive vehicles it has to show up in makes like Cadillac, BMW, Mercedes, etc. first. Once costs drop, it will move into different market segments.

hampden wireless

Kevin wrote:
"They could have created an engine with significantly better fuel consumption, but instead went for more power"

Well they did make the engine with better fuel consumption... in fact they made it FIRST. From the article..."The 3.6L V-6 engine is GM’s third engine variant offered with direct injection technology. GM offers an Ecotec 2.0-liter four-cylinder Turbo engine with direct injection on the 2007 Saturn Sky Red Line and Pontiac Solstice GXP roadsters. Since 2004, Opel has offered a naturally aspirated Ecotec 2.2-liter direct injection engine in Europe."

So they made a 2.0 l 4cyl direct injection FIRST. This new 6cly will more often replace an 8 cyl in GM's lineup.

Stan Peterson


Your request has already been met. The Ecotec 4 all aluminum, I4, has GDI and dual VVT and DOHC, and balance shafts and turbocharging if you want it, in a 2 liter version. Adds up to 260 HP and EPA mileage figures of 21-29 in a 3100 LB Pontiac or Saturn.

The non turbo version produces 174 HP but no significant mileage improvements at 2.2 liters.


As some have already said they already have high tech 4 bangers.. this is thier new v6 to replace all the old big engines.


The Cadillac STS has to have a certain minimum power or it won't sell. And if you don't sell any cars you aren't improving mileage at all, or anything else.

IMO the STS should go away but marketing is not quite that simple. They need a car in the tier above the CTS. The STS is what they have, hence, the STS is what they offer.

Buyers above $50K won't care if gas is $6/gal. They will care about performance. So Cadillac can only do a little about mileage for now.


I think the complaining is because GM is no longer a leader, but is always playing catch-up to the Japanese these days.  Ditto the barbs aimed at the union:

  1. The retiree benefits are not sustainable, and have driven the abandonment of the small-car sector.
  2. The taxpayer should not assume the costs for benefits over and above Medicare.
Excessive benefits are just one luxury we can no longer afford.


Whats going on with gm is simple.

The gov xant afford to let gm fall as the benfits are MASSIVE and cover far too many people.

They cant even afford to have the benifiys lowered too much becuase so many count on that money and its shrinking would tank many STATE econs thus hurting the entire us.

So all they xan do is wait for them to slowly die and hope gm holds up under the pressure.


Union extortion has forced GM and many other US manufacturer’s legacy costs to become over 50% of their operating budget. This along with other factors makes US jobs non-competitive with the east. When the manufacturing jobs go to Communist China you can blame union and corporate greed.

This is much like FDR’s New (socialist) Deal "entitlement" programs have created $TRILLIONS in US public debt. Much of this debt is owned by the People's Republic of China. When the economic power transfers to Communist China, so does the political and military power. You can lay blame squarely with the US people's greed for their neighbor’s tax money. The US and “freedom” may have won the Cold War, but we are losing the Economic War. The Chinese have silently watched and learned how to defeat us without a shot being fired.


Did the wheel need re-inventing?


I used to live in the UK, which used to have relatively cheap gas, this evolved to more of a European model of taxation (i.e.high!) over a 10-20 year period.

The reaction of the auto manufacturers was as follows:
British, couldn't adapt and died a long and very painful death
American, Japaneese, European, built more efficient cars, switched to Diesel, and crucially, figured out that there was a definate market for small and medium sized luxury cars, i.e. cars that were frugal but with luxury refinements. I cant see why this is any different in the US, except the US manufacturers are not responding to the need.

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