By: Mark Williams
There was a time when making the strongest, most powerful, hardest-pulling V-8 for a half-ton pickup was all you needed for success, but the world is changing. Just last year, the new Ford F-150 (winner of several Truck of the Year accolades) came out with two midlevel 4.6-liter V-8 options — one in two-valve-per-cylinder configuration, the other in three-valve-per-cylinder dress. Now, Toyota is coming to the half-ton market with a completely redesigned midlevel V-8 option. Replacing the aging 4.7-liter V-8 that was developed all the way back in 1998, the Tundra will debut an all-new, all-aluminum 4.6-liter V-8 at the 2009 Chicago auto show, along with two other new option packages.
Significant cost-cutting means Toyota won’t have a press conference at the show this year, but the company did give us quite a bit of background on the new engine (see videos). As you might imagine, this will be an important engine for the Tundra (and Sequoia) lineup -- especially with so much attention focused on full-size pickups and SUVs. While we haven’t heard anything official yet, we’d guess Toyota has bigger plans for both the new 4.6-liter V-8 and the new six-speed transmission, as well as what it will mate to in the future. For now, here’s the story.
According to David Lee, University of Toyota product administrator for truck and SUV, Toyota engineers had very specific targets in mind when designing the new engine. The all-new alloy engine is smaller than the previous entry-level V-8, but they wanted it to be more powerful, more fuel-efficient and lighter. Of course, fresh off their iForce 5.7-liter V-8 design, they had some pretty good ideas about how to accomplish their goals. Sharing many of its technologies with both the 4.0-liter V-6 and the 5.7-liter V-8 engines, the new middle V-8 uses an aluminum block and two alloy heads. It provides almost 100 pounds of weight savings compared to its 4.7-liter counterpart. Although the cylinders are exactly the same diameter, 3.70 inches, the stroke of the pistons is just a touch shorter, at 3.27 inches in length. Engineers also bumped up the compression ratio (to 10.2:1) on the 4.6-liter V-8 to allow for a cleaner, more controlled burn in the chambers. The results are significant.
Toyota is stating the new V-8’s specs at 310 horsepower at 5,600 rpm and 327 pounds-feet of torque at 3,400 rpm. Although these numbers may not sound hugely impressive -- especially compared with its direct competitors -- this new engine does offer the best horsepower and torque for its size, especially when you look at horsepower and torque per liter (see chart).
As for fuel economy -- an all-important number nowadays -- EPA numbers haven’t been finalized, but Toyota is saying the numbers will be as good as, if not better than, the leading V-8 numbers in the class, which means upward of 15 or 16 mpg in the city and a minimum of 20 mpg on the highway. These numbers are most likely for the regular cab, short-bed, two-wheel-drive model.
Toyota says the performance improvements are largely due to one very important change to the new engine: a dual VVTi valvetrain. The middle engine choice still offers dual overhead cams and four valves per cylinder, but it now has a chain-driven system that also allows for independent adjustability between the intake or exhaust sides of the camshaft. (The previous 4.7-liter V-8 only had VVTi on the intake side of the cam). Additionally, just like its 5.7-liter V-8 big brother, this new engine has roller rockers and hydraulic lifters to reduce friction losses and to improve throttle responsiveness.
It’s also worth noting that this is the first Toyota engine to offer a water-cooled, computer-controlled EGR -- sitting directly on top of the engine, right under the plastic engine cover -- which allowed engine tuners to more accurately control the combustion burn temperatures through more of the power band, which means more overall power; a wider, flatter torque curve; and cleaner emissions out the tailpipe. Under light engine loads the EGR system also pushes non-combustible gases into the cylinders, creating a kind of pneumatic displacement that requires less fuel to burn the charge and helps improve fuel economy.
On the intake side, the 4.6-liter has a two-stage intake that channels intake air down two separate paths, depending on whether the engine is looking to maximize low- or high-rpm power. Although this sounds like a huge amount of technology that could potentially clog up the engine compartment in a tangle of tubes and electronics, the physical dimensions and the space it takes up under the hood is about the same as the old V-8. Of course, the new engine is lighter because of the alloy block material, but it’s also a touch wider at the top of the cylinder heads, where all the new dual VVTi technology is hiding. Still, looking into the engine compartment you’d be hard-pressed to see any significant size distinction between the old and new engines.
This new engine isn’t the only trick up Toyota’s sleeve; along with the new V-8, the automaker also has a “new” six-speed transmission (the A760E). Some might have guessed Toyota would use the six-speed it already pairs with its 5.7-liter V-8, but after considerable testing engineers concluded that transmission wasn’t a perfect match for the horsepower and torque output of the smaller V-8. Instead, they decided to slightly modify the gear ratios of the existing five-speed auto and include another cog without having to increase the size or weight of the transmission itself. As a result, 1st gear is a respectable 3.52:1 and 6th gear is a low-rpm-running 0.59:1. Preliminary fuel economy numbers are calculated with the lower (numerically) of the two ring-and-pinion gearsets offered (3.91:1 and 4.10:1). We’re guessing Toyota is leaving itself plenty of room for a possible high-mileage option package down the road, possibly offering 3.55:1 or 3.73:1 axle gear options. Some major players in the segment are using 3.15:1 gears for their high-mpg packages.
The new engine and transmission pairing will be available as an option on the 2010 Tundra starting in April 2009. Expect Sequoias to get the same entry-level V-8 option soon after that. Toyota sold just under 20,000 4.7-liter V-8s last year, and it’s hoping to at least match that number in the coming year. According to Toyota’s marketing gurus, the smaller V-8 is for the customer looking for a work engine that gets better fuel economy, offers enough power to do a good amount of work, and isn’t too complicated to work on or keep running smoothly. Clearly, it looks to be a step in the right direction, but whether or not it’s enough to get people interested in big pickups and SUVs again remains to be seen. For now, we’re guessing this will be the target other manufacturers will have to hit for several years to come.
We’ll have more details when we get a chance to do some real-world driving and towing with a production model. Stay tuned.
Drivetrain layout: Front-engine, RWD or 4WD
Engine type: 1UR V-8, aluminum block/heads
Valvetrain: DOHC, four valves/cyl., chain drive (dual VVTi)
Displacement: ci/cm 3:281.2/4608
Bore & stroke: 3.70 x 3.27
Compression ratio: 10.2:1
Horsepower: 310 hp @ 5,600 rpm
Torque: 327 pounds-feet @ 3,400 rpm
Transmission: A760E six-speed auto
- 1st 3.52:1
- 2nd 2.04:1
- 3rd 1.40:1
- 4th 1.00:1
- 5th 0.72:1
- 6th 0.59:1
- Rev. 3.22:1
Ring and pinion: 3.90:1, 4.10:1
Fuel efficiency: 15/20 mpg city/highway (preliminary numbers)
Emissions cert.: ULEV II