by Jim Kerr
Click image to enlarge
Ford’s new 2004 F150 pickup will be arriving at dealerships in a few weeks and the 5.4 Triton engine has had some major redesigns to increase it’s horsepower to 300 ponies and 365 ft. lb. torque. Several changes have been made to this engine including new intake and exhaust manifolds but the new cylinder head design is one of the major contributors to the power now available.
Still utilising a chain driven overhead camshaft design, the Triton’s new heads feature three valves per cylinder instead of the more conventional two valves. Most engines use two valves per cylinder, one intake and one exhaust valve, while some performance engines use four valves per cylinder (two intake and two exhaust valves). There are several advantages to using more valves, and a couple disadvantages.
With two valve cylinder heads, the valves have to be quite large to allow sufficient airflow into the engine and exhaust gases out. The problem with larger valves is that they open very close to the edge of the cylinder and some of the airflow is blocked. Another problem with big valves is that they are heavy. Stronger valve springs, stronger valve train components, and a more gradual camshaft profile are required to keep the valves from bouncing at high rpm’s due to their inertia.
Four valve cylinder heads have much smaller and lighter valves so the problems with two valve designs are eliminated, but now there are new problems. Four valve heads have a lot more parts, so they are more costly to build and repair. Often, dual overhead camshafts are used to operate these valves, so there is the complexity of additional camshaft drives. Another problem with four valve head design is that with so much of the space used by the valves, it is difficult to make room for the sparkplug!
2004 Ford F-150 3 valve sectional head. Click image to enlarge
Ford’s Triton three valve cylinder heads are a compromise between complexity (and it’s cost) and breathing ability. Two intake valves are used to allow ample airflow into the cylinders. Only one exhaust valve is used, but because exhaust is forced out of the engine by the piston during the exhaust stroke, the exhaust flow is still quite efficient. Exhaust ports on the cylinder head have been reconfigured in an upside down D shape to improve exhaust gases flow from the head and into the freer flowing exhaust manifolds.
All three valves are operated by one overhead camshaft. Overhead camshafts require more complex drive mechanisms than engines with the camshaft in the cylinder block, but the complexity is offset by the improved port designs allowed. Camshaft in block engines use pushrods to transfer the movement from the camshaft to the valves, but the pushrods pass through the cylinder head so port design is often compromised to accommodate them.
The sparkplugs used on this engine have a small tip (just a little larger than a pencil) so they can be centrally located in the cylinder head between the three valves. This position improves combustion but required a new design that locates the sparkplug threads into the middle of the plug with a long but small extended shell to hold the electrodes. Not only do they work, but sparkplug life has been extended as well.
Variable camshaft timing is another added feature to provide more power and control emissions. The camshaft can be moved by computer-controlled hydraulic pressure up to 50 degrees in relation to the crankshaft depending on engine speed and load conditions.
While there are many other small improvements, two more are noteworthy. Electronic throttle control helps optimise power at all throttle positions and provides a smooth progressive feel to the power. Charge-Motion control valves in the intake manifold just below the injectors close electrically to induce turbulence in the intake for increased burn efficiency at lower rpm’s. At higher engine speeds, the computer opens the valves for undisturbed maximum airflow.
Internal combustion engines in automobiles have been around well for over a 100 years now. Even after all those years, there are bright people out there still coming up with ways to improve both engine efficiency and power while reducing emissions. Some of them were definitely working on Ford’s new Triton V8 truck engine.