- Feb 22, 2006
High-end V6s - the Lexus direct-injection 3.5L and Cadillac 3.6L
No, that's not some sort of captured alien - it's Toyota's rather unique way of showing off its latest 2GR-FSE direct-injection V6. We're going to take a look at this engine, which is interesting primarily for the means that it introduces fuel into intake air. We'll also check out what's going on with GM's so-called "High Feature" DOHC V6 that currently sees use in the Cadillac CTS and Buick LaCrosse, and will soon be available under the hood of the upcoming Saturn Aura.
Sorry, Lexus fans - the poor lighting combined with the acrylic walls of the display enclosure to result in a terrible environment for photography. You'll have to take my word that the bottom end of this engine is, well, rather mundane when compared to what's going on in the intake manifold and cylinder heads.
If you look at the first picture, you can see that Toyota has avoided the usual cutaway techniques and instead takes a slice from the middle of the block. This chunk o' engine is motorized, and runs up and down while the engine is on display. It makes it difficult to see what's going on in the bottom end, but does an excellent job of showing off the top end.
Check out the vertical intake runners; this looks more like velocity stacks on a race engine than something we'd find in a luxury automobile.
Check out the cool little roller rockers that are used to transfer motion from the cam lobes to the valves. They add a bit of packaging height, but they also multiply valve lift and therefore require smaller cam lobes. There's the benefit of reduced friction as well.
We can also see the coil-on-plug (COP) assembly tucked between the two camshafts. It's extremely slender, and allows a narrow "included valve angle". This is important for two reasons: 1) Quite simply, it reduces packaging bulk; and 2) Narrower valve angles lend themselves to better intake and exhaust port geometry. The size of this coil is one of those "little details" that impacts so much of the engine's design.
The real story, though, lies just above and below the intake runner. You can see that there are actually two injectors for each cylinder - the top one is a standard port fuel injector, while the bottom one injects fuel directly into the combustion chamber. The two injection systems are used together to optimize the fueling over the engine's operational envelope.
As described in the January 2006 issue of SAE Automotive Engineering International, the system primarily relies on the port injection system when low engine speeds are combined with high loadings. Under these conditions, a direct injection scheme cannot properly atomize the fuel, and so approximately 60% of the fuel is provided by the port injector. As engine speed increases, the direct injection system takes over more of the fueling responsibility, until eventually it provides 100% of the necessary go-juice. Obviously, there some complex calculations going on to determine the optimum fueling over the engine's operating range, and that has led to over 300 patents being issued to Toyota concerning the design of this system.
There's a 7 increase in torque from the system, some of which comes from the 11.8:1 compression ratio that's enabled by the use of direct injection. Better yet, the benefits apply to the entire powerband, so this is a feature that will be useful to most any driver.
The dual injection system also reduces cold-start emissions. The port injection system dumps a bit of fuel on the back of the closed intake valve; when that valve opens, the fuel is evenly distributed throughout the cylinder. As the piston approaches the top of its travel, the direct system injects a bit more fuel into the cavity on top of the piston. The total air/fuel mixture in the combustion chamber is slightly lean, but the mixture is significantly richer in the area around the spark plug, making it easier to ignite in a cold engine. The result is quicker warm-up and smoother operation when cold.
The engine produces 306 HP at 6400 RPM, and 277 lb-ft at 4800 RPM; a remarkable accomplishment for a luxury-car V6.
Next we'll take a look at GM's "High Feature" V6. Where as GM's V6 lineups have previously involved more players than the average football team, the company is moving forward with plans to use only two V6 engine architectures from here on out - the updated pushrod design that is being sold as the 3.5L and 3.9L, and this DOHC design.
Like every other modern engine, it's apparently necessary to cover this one in a large, non-descript plastic shroud. I'd always figured that hoods were the part of the car designed to cover up engines. Seriously, such covers are as much about reducing noise as they are about decreasing visual clutter.
Here's the left rear of the engine. GM did a nice job of minimizing the packaging height, as can be witnessed by how closely the decorative cover hugs the cam covers. There's the now-typical swooping exhaust manifold as well. Just to the left of the manifold in the photo, we see what appears to be the oil filter. The up-top positioning of it is probably nice for service, but I'm guessing that there's a bit of a mess upon removal.
There's the chain drive for the camshafts, as well as variable-valve-timing (VVT) actuators on both cams.
This appears to be a well-designed intake tract (255 HP at 6200 RPM and 252 lb-ft at 3200 RPM doesn't come by accident). The intake manifold features a shorter path that what we've seen on other engines; some of that is likely due to a bit of bias towards higher-RPM power, while there were probably also tradeoffs made to minimize packaging volume (let the intake manifold guys have their way, and we'll be driving around with all manners of bumps sticking up through the hood).
The intake path into the head isn't quite as vertical as other engines, but it shows a considerable improvement over the Northstar V8 (which has its roots in the original Quad 4). Note that this engine also uses roller rockers to actuate the valves, and there's some nice beehive valve springs in there as well.
I mentioned the compactness of Toyota's coil assembly; compare it to the slightly larger unit used here on the GM engine. This relatively minor increase in packaging volume results in the cams being pushed out slightly, which affects the intake and exhaust tracts while slightly increasing the size of the head.
The flat-top pistons contribute to a 10.2:1 compression ratio. And, yes, that's another crankshaft position sensor setup there, just ahead of the flywheel.
This is yet another example of a "deep-skirt" block, where it extends well below the centerline of the crankshaft. Also take notice of the amount of material in the valley of the block (above the crank and between the cylinders). Presumably, all that webbing is there to stiffen the block and reduce NVH (noise/vibration/harshness).