To achieve high horsepower levels with the Ford DOHC 6 cyl engine, the gas exchange process (wet flow cylinder filling with air/fuel ratio, followed by dry flow purging of burnt gases) needs to be matched to other criteria of the engine. Fortunately, the standard cylinder head is designed to exchange gases in a reasonably efficient manner, and like almost every internal combustion engine it responds favorably to reworking. Of particular benefit is the coordinating of the inlet airflow and valve movement with the downward motion of the piston.
This can be achieved with fast opening/closing camshafts and efficient porting. In an engine equipped with hydraulic lifters, the valve movement is relatively slow as the lifter takes up some of the valve acceleration as it constantly adjusts itself.
To move the valves faster from their seats (hence increasing cylinder filling/purging) the opening/closing rates of the camshafts must be increased. Hydraulic lifters are not up to the task, so a “solid” lifter is fitted.
Our range of matched cylinder head/cam packages are tailored to precisely match the requirements of high performance street and racing applications, right up to 2000+ HP monsters.
The DOHC 4 valve per cylinder head is very well designed and suits forced induction applications due to the high percentage of exhaust to inlet flow, a short, semi pent roof combustion chamber (66 cc average in BA-BF Series), two small squish areas and a centrally located spark plug for fast and efficient flame propagation.
Valve springs are always a problem in forced induction DOHC engines as comparatively light reciprocating valvetrain mass usually means a short, light spring is fitted as standard equipment. This usually limits the number of valve spring options available, however we have many different springs available to suit almost every conceivable application – please refer to our valvetrain section.
Forced induction engines also need good quality valves, especially on the exhaust due to increased heat. The OE high nickel exhaust valve (identifiable by the O forged in the head) is good for moderate performance applications and for extreme duty applications we have USA made single groove Inconel stainless valves with flash chromed stems and hardened tips. The hi flowing exhaust port also produces high exhaust gas temperatures, typically 200-300 degrees F higher than other turbo engines, which again highlights the need for an extreme duty exhaust valve.
O-ringing of combustion chambers is required when using a copper head gasket and is part of our DLM Spec Series pro-race engine packages.