Subscribe to a magazine

2010 Toyota Tundra 4.6L V8 Engine Review - First Drive

Front View Drags
John Stewart | Writer
Posted August 1, 2009
Photographers: Courtesy Toyota Motor Sales USA

How Toyota Gets More Out Of Less

There is a new grille and a few other minor changes for 2010 Toyota Tundra, but the big change is under the hood.

We've always felt the new Tundra is a solid pickup truck, big enough and strong enough for heavy jobs in the real world. The 5.7-liter V-8, in particular, has always stood out as a hot-rod power plant with advanced features.

But in the last year, the pickup truck market has changed, and mileage has become a more important selling point. It's now possible to get a full-size pickup truck that can do 21 mpg on the highway from Ford and GM, although you have to order a narrowly specialized 4x2 package to do it. For the average 1/2-ton, 19 or 20 mpg on the highway has become the new standard, and until now, Toyota did not have a pickup that could compete in that range.

Enter the newest Tundra engine, the 4.6-liter V-8. It delivers more horsepower and more torque than the prior 4.7 V-8, and it has a six-speed transmission behind it to help the 2010 Tundra get much better mileage. Performance-wise, it's clear that the 4.6 V-8 is no 5.7, but nothing is, and it's certainly a much more advanced engine than the older 4.7 V-8. According to Toyota, the 4.6 will deliver the best combination of power and fuel economy among any standard V-8 in the full-size pickup segment.

How do they do it? The new V-8 is essentially a slightly destroked version of the 4.7 V-8, but with all the tweaks that the optional 5.7L received when it was developed.

There are only a few changes inside the 2010 Tundra, but Toyota will offer a work truck version that has a plain interior (shown) at a reduced price.

That includes Dual Variable Valve Timing (VVT-i). Dual VVT-i controls valve timing and overlap on both the intake and exhaust valves. The older 4.7 V-8 had an earlier version of Variable Valve Timing (VVT), which allowed for advancing or retarding the timing of the intake valves only. Dual VVT-i allows for controlling both intake and exhaust valves, in effect creating a more elastic variable cam profile. That's a big deal.

In an ordinary engine, the cam profile--determined by the shape of the cam lobes on the camshaft--works best within a certain rpm range, forcing a choice between low-end torque and high-end power. At high rpm, an engine requires more air, so the longer the intake valves can stay open, the more top end power the engine can make. But if the cam keeps the valves open longer, as with a racing cam, problems start to occur at low rpm, reducing torque and ability to idle, and creating the tendency for unburned fuel to exit the engine when both intake and exhaust valves are still open. So you end up with lower engine performance and increased emissions.

Dual VVT-I manages both the intake and exhaust valves to make sure the timing is optimized at low rpm (for more torque) and high rpm (for more horsepower). Another benefit is that it allows for faster heating of the catalytic converter, and with less unburned fuel exiting the combustion chamber, there is improvement in emissions and operating efficiency. By the addition of Dual VVT-I, we would expect to see the 4.6 make more power than the 4.7 at higher rpm, and make the same torque with smaller displacement, with less wasted gas. And that's exactly what it does.

The new standard 4.6L V-8 may be smaller than the 4.7 V-8 it replaces, but it's more powerful and much more efficient. Engineering transferred from the optional 5.7 i-Force V-8 help make the difference.

Another factor at work is that with better electronic controls on the 4.6, compression can be slightly increased. Just like the 5.7, the new 4.6 runs on a higher compression ratio (10.2:1 instead of 10:1) than the old 4.7. More compression means more power with every stroke.

The new 4.6 V-8 also uses water-cooled exhaust gas recirculation (EGR), which lowers peak temperatures inside the combustion chamber. In the new 4.6, a computer controls the timing and amount of cooling the exhaust gas receives before it is recycled through the combustion chamber, so the combustion process is never over-cooled. Generally speaking, cooled EGR provides an emissions benefit, but it's also known that the technique improves overall efficiency, which translates into better mileage.

The new engine has a cast-iron block, like the current 4.7, and both use 32-valve aluminum heads. (The 5.7 block is aluminum, to reduce weight, which also adds expense.)

All Tundra engines, even the 4.0 V-6, have the same bore: 3.70 inches. Toyota gets more displacement out of the truck engine line by adding stroke, permitting the manufacturing and service advantage of a standardized piston. In the case of the 4.6, the engine has same bore as all the other V-8s, but a shorter stroke. With a shorter stroke, it revs higher, so it can make more peak horsepower.

More power is all good, but getting more power with better mileage is the Holy Grail. Gearing has a lot to do with it. If you can make the power to pull taller gears, you'll get better mileage without sacrificing performance. In the case of the 4.6, taller gearing comes from a slightly taller axle ratio and a much taller Overdrive gear in the six-speed transmission. The "new" six-speed is essentially the same five-speed unit used with the 4.7, but with one extra ratio, a 0.586:1 overdrive Sixth gear. All the other ratios are exactly the same. Just by adding the tall Sixth gear, a much more efficient final "cruising ratio" can be achieved. Formerly, the five-speed allowed for an overall cruising ratio of 2.94:1 (multiplying the axle ratio of 4.10 x 0.716 Fifth gear). With the six-speed's taller Sixth gear at 0.586, plus the ability to pull a taller 3.901:1 rear end ratio, we get a cruising ratio of 2.29:1. Net result: Highway mileage jumps to 20 mpg, when it was 17 for the 4x2 4.7 Tundra, and just 16 mpg for the 4x4. That's an improvement of four mpg, or about 20 percent. Performance is about the same, and in fact, the maximum towing rating has been increased from 8,500 pounds to 9,000 (that's on two-wheel drive models).

To get a sense of how it feels, we spent a day track testing a 2010 Tundra, measuring acceleration both loaded and unloaded, with a little highway driving mixed in. The idea was to quantify how much acceleration had been given away in the quest for better mileage.

We tested the new powertrain for acceleration, loaded and unloaded, and found that it would hit 60 mph in under nine seconds with a 1,000-pound load in the back.

Our test unit was a pre-production 4x4, not an actual production unit, but likely to be quite representative of the final product in terms of drivability. With the new Tundra loaded with 25 40-pound bags of salt, we found the 4.6 would power the truck to 60 mph in less than 9 seconds, with the fastest run at 8.92 seconds. The 2010 Tundra has a standard Automatic Limited Slip (ALSD) that allows for a little wheelspin before locking the diff. It's designed for use on sand or mud, but the drag strip at Irwindale Raceway is a sticky surface, so we were better off without any form of traction control. Our fastest times came when we switched everything off, which happens when the traction control icon on the center stack is held down for three seconds, three times in a row. With the traction control on, there was a quick chirp and a brief moment of hesitation before the truck began acceleration. With the ALSD off, the truck just moves out without any hesitation. At about 3,400 rpm, the engine begins to pull like a train, and continues ripping up to the 5,600rpm shift point. We tried a few runs shifting manually, which the transmission permits, but we kept bumping into the rev limiter and in the end, went much slower.

Empty, our fastest runs were just under eight seconds, with our best 0-60 time allowing the truck to cover 407 feet in 7.91 seconds. That's not all that much slower than a Tundra with the hot-rod 5.7 V-8, for which reported 0-60 times have been in the 7.20 to 7.15 range. In an 1/8-mile race, we guess that's about a truck length, but more important would be how responsive the Tundra is with the smaller engine. With no load, it's obvious the truck moves out more readily at part throttle, and loaded, it still feels like there is midrange power to burn. Overall, the difference between loaded and unloaded acceleration at full throttle is not really that noticeable, other than slightly higher shift points under load. We were pleased at how well the test unit handled the first 1,000 pounds; our guess is that at maximum load--1,255 pounds as indicated on the door sticker--it would still feel stable and have passing power in reserve.

On the highway, the new Tundra shines, cruising easily, hitting 73 mph at about 2,000 rpm. It's also unusually quiet. Preliminary Toyota spec sheets do not mention any change in the way the 2010 Tundra is insulated against noise or vibration, but to our ear, the truck seems substantially quieter.

We did not attempt any off-highway testing, but there are certain changes for 2010 that may have some impact. For one thing, the seven-pin towing hitch connector now sits above the hitch to improve departure angle, so it won't get ground off when the truck drags the hitch on the way out of a deep ditch. Plus, we think the fact that the new traction control system is switchable may make it easier to use on sand or in mud. However, the taller overdrive and rear axle ratio does make for a slightly higher crawl ratio, which might impact four-wheeling ability. Our guess is that the 3.91:1 rear end, combined with a 2.62:1 low range gear, leaves plenty of crawling power and downhill control, but that's something we'll be taking a much closer look at during Pickup Truck of the Year testing.

ENGINE SPECS
Engine: 4.6L V-8 4.7L V-8 5.7L V-8
Bore x stroke (in): 3.70 x 3.27 3.70 x 3.31 3.70 x 4.02
Compression ratio: 10.2:1 10.0:1 10.2:1
Horsepower@ rpm: 310 @ 5,{{{600}}} 276 @ 5,400 381 @ 5,600
Torque (lb-ft) @ rpm: 327 @ 3,400 313 @ 3,400 401 @ 3,600
MPG: 15/20* 13/16 (4x4) 13/17 (4x4)
Transmission: 6-spd auto 5-spd auto 6-spd auto
Axle ratio: 3.909:1 4.100:1 4.{{{300}}}:1
Emissions class: ULEV II ULEV II ULEV II
Cruising ratio: 2.291:1 2.936:1 2.528:1
Crawl ratio: 36.02:1 37.78:1 37.52:1
*(mfg est.)

Comments

Advertisement