How dedicated camshafts help improve engine performance and fuel economy.

[dascrow]

All Toyota Tundra engines feature dual overhead camshafts (DOHC). This means there are two camshafts placed at the top of each cylinder head for a total of four camshafts on V6 and V8 engines. One camshaft on each head opens and closes the intake valves while the other camshaft operates the exhaust valves. (Actually the valve springs close the valves but the camshaft lobes control the operation and determine when valves return to the closed position.) Each cylinder has four valves: two intake and two exhaust.

This is the standard engine design in almost all high-performance cars and racecars. Some trucks like the Ford F-150 have a single-overhead-camshaft (SOHC) design with a single camshaft located on top of each cylinder head. On the Ford, this cam can operate a single intake and single exhaust valve per cylinder, or on the 3-valve motors it operates two intake valves and one exhaust valve. Other ½-ton trucks like the Chevrolet Silverado, GMC Sierra and Dodge Ram use a cam-in-block and two-valves-per-cylinder design in most of their engines. This means a single camshaft operates all the valves through a complex and heavy arrangement of lifters, pushrods and rocker arms.

Because the Tundra’s camshafts are placed almost directly over the valves, the valve operation is much more precise, even at high engine revs or RPM. Engine breathing is also more efficient over a wide range of engine speeds with four valves controlling airflow into each cylinder. Remember, an internal combustion engine is an air pump in its simplest form. Multi-valve engines allow more air and fuel to enter the cylinders, which in turn produces more useable power and increases fuel economy.

DOHC makes it much easier to implement variable valve timing. To operate at peak efficiency, the airflow in and out of the cylinders must be carefully managed. Proper valve timing is critical to engine operation. Too much air or not enough at different engine speeds will adversely affect performance and fuel economy. Variable valve timing adjusts the valve operation in relation to the position of the piston. The Tundra’s engines feature Variable Valve Timing w/ intelligence (VVT-i), a unique mechanism that selects the ideal times for the intake and exhaust valves to open and close. By changing the valve timing, VVT-i eliminates the traditional tradeoff between low-RPM torque and high-RPM horsepower while at the same time improving fuel efficiency.

A standard VVT-i found on the Tundra’s V6 and 4.7-liter V8 engines changes the timing of the intake and exhaust valves at the same time and relative to each other. The Tundra’s 5.7-liter i-Force V8 engine goes one step further with Dual Independent VVT-i. This system can change the intake and exhaust valve timing independently of each other for even greater precision and airflow management. As a result, 90% of the torque in the 5.7-liter V8 occurs from 2400 RPM up to 5500 RPM. This wide-range or torque band gives the Tundra incredible pulling power and fuel efficiency.

Some other benefits of DOHC engines are that the:

• Engine can be specifically engineered to improve fuel economy
• Engine can be specifically engineered to improve performance
• Engine burns fuel completely, reducing emissions and improving fuel economy

[source] Toyota

[CJ$]

Originally Posted by dascrow

As a result, 90% of the torque in the 5.7-liter V8 occurs from 2400 RPM up to 5500 RPM. This wide-range or torque band gives the Tundra incredible pulling power and fuel efficiency.

Does this mean that the best fuel economy occurs when RPMs are between that range? I try not to go above 2,000/2500 when I accelerate. Is this worse on the gas mileage?

[Matthewo_03]

Originally Posted by CJ$

Does this mean that the best fuel economy occurs when RPMs are between that range? I try not to go above 2,000/2500 when I accelerate. Is this worse on the gas mileage?

yea mee too

[blackdemon]

I'm also jumping on that ban waggon. I'm curious on that subject due to the fact that it appears to me I get better fuel economy abve 2k rpm, or about 75 to 80mph.

[FirstToy]

That is very interesting! I am off to South Dakota next week, so I will experiment with different RPMS.

[Nukedog]

I get MUCH WORSE fule economy in any vehicle i have EVER owned when above 1800rpm for any length of time. More RPM requires more FUEL.

At 60mph you will get about 21mpg with this truck. At 75mph you get about 19mpg...

[Mickey]

Originally Posted by Nukedog

I get MUCH WORSE fule economy in any vehicle i have EVER owned when above 1800rpm for any length of time. More RPM requires more FUEL.

At 60mph you will get about 21mpg with this truck. At 75mph you get about 19mpg...

I agree with Nukedog at 80mph I get 17.3 and depending on terrain and weather it could go down to 16.7mpg....Hard to believe that statement.....

[FirstToy]

Originally Posted by Mickey

I agree with Nukedog at 80mph I get 17.3 and depending on terrain and weather it could go down to 16.7mpg....Hard to believe that statement.....

It doesn't work! I tried different PRMs (12 hours on the road) and the best was at 65 MPH for and average of 24.5 MPG (no wind and very few hills) The worst was 8 MPG at 90 MPH (wind and hills and stupid ass drivers), but it was fun there for a bit The higher the RPM... the worse the gas mileage.

[blackdemon]

Guess is different from place to place, I take a trip about once a month to visit family in TJ, including a 3k+ft mountain climb. I've taken different trips and set the cruise at 65 from the beginning of my trip -42 ft below sea level, all the way to the border, the most I've seen has been around 15.5 - .7. I've floored it in small spurts here and there, more in the mountain climb than any where else, and I've seen better improvements to 16.8 - .9. Mind you this is manually, not by what the cpu says. Cpu usually states 14.3 to 13. I'm taking another trip this weekend as well, and I'll repost again.

[FirstToy]

Originally Posted by blackdemon

Guess is different from place to place, I take a trip about once a month to visit family in TJ, including a 3k+ft mountain climb......

Well... I actually could not believe it either I filled up when I left. I drove the 150 mile stretch to the gas station where I normally fuel up, and I put 6.12 gallons of gas in. I drove this stretch in the morning when it was cool... about 55 degrees. It was a nice morning, there was no wind, very few cars and very few hills. I set the cruise control, and I bet I only passed 1 car. I was on a secondary highway that for the most part is very smooth. It was a perfect drive, and one that never ever happens with me. I did not see that kind of mileage the rest of the trip. The rest of the trip was more in the range of 15 to 16 MPG. When I said I got about 8 MPG at 90 MPH, that was an average from what I read from the truck.

[blackdemon]

well, out here we usually get pretty high winds, usually a 62 mile stretch of head on wind. This time a year it usually stays in the hundreds up until 8 o clock when it cools down to about 90. In the mountain climb sometimes i get about 8 as well out of the cpu, but I'm usually haulin' to pass jokers on the right and left lanes.

[Mickey]

One of my trips to Savannah I got 24.5mpg at 55mph. I couldn't replicate it on my return trip. The avg I get on most trips is between 20 - 22mpg at 60 - 70 mph. The rpms are at 2,000 or below so I never hit that range between 2400 - 5500 rpms. Most vehicles I had when driving economical was around 1700 - 2000 rpms was the best mpg's off those vehicles.

[blackdemon]

I did my weekend trip to TJ on Saturday. we departed about 10am, and it was just over a 100. Set the cruise at 65mph, went across the border, and waited in line for about 50 minutes, the cpu stated 15.0mpg, manually I tallied up 15.4mpg that was a 161 mile trip and I pumped slightly over 10 and a half gallons. I got to make another trip this week, for a doctor's appointment. I'll try 70 this time, and will repost.