From Mechanical Database
The CHV engines were a new design originally made for Ford Escorts. They were made from 1.6L to 2.0L sizes in the U.S. CVH stands for "Compound Valve angle Hemispherical" combustion chamber. These all are cast iron blocks with aluminum heads. The camshaft is mounted in the head and the lifters also serve as pushrods actuating the rocker arms.
This engine is very durable and has stood the test of time. Up until recently, it was still being produced 21 years after it was first introduced. The most common problems are warping the head by overheating the engine or breaking a timing belt. The timing belts should be changed every 50,000 miles. Unfortunately, this engine group along with the Zetec was phased out in 2005, and replaced with the Duratec line of engines.
All the engines are similar in design and function but the 1.9/2.0L has a taller deck height to achieve the longer stroke. Many parts are interchangeable, many are not. There are at least 6 different piston designs and they must be used with the proper cylinder head casting. If not, clearance problems or low compression will result.
The best power producing heads are from the 1.9L GT / hemi design. These heads used the 42mm intake valves and 37mm exhaust valves. The valves are unshrouded and with a little help from the grinder, will make good horsepower numbers. The earlier 1.9L heads are very similar but had a high swirl combustion chamber and requires removal of a lot of aluminum to work well. The ports and valves are identical. The poorest designs are the CFI and SEFI injected engines made from 1987-1996. They have the smaller 39mm intake valves and the SPI an offset (with the valve centerline) intake port intended to increase swirl in the combustion chamber. The exhaust valve size was reduced to 34mm. They do respond well to proper porting. All the exhaust ports and bolt patterns are identical in all CVH engines but the intake side varies quite a bit based on the style of intake system used.
The newer SPI (Split Port Induction) engines have the larger 37mm exhaust valves and the largest intake valves ever put in a CVH engine measuring 44.1mm. Half the combustion chamber is similar to the hemi head but he other side is filled in. They still have the potential to flow very well. There are two intake ports in the head leading to one valve, the crescent shaped one for high torque and the round one for high rpm power. There is a control assembly between the head and the intake manifold that opens butterfly valves above 3000 rpm for added top end power. This setup works reasonably well but does cause slower acceleration and a part throttle surge in low gear when it opens. As Ford designed it, the valves take several seconds to fully open.
Larger valves are nice but very expensive to install as the pressed in valve seat must be removed, machined out, and a larger seat installed. Also the valve reliefs in the pistons must be machined to match the valves. In most cases, the added expense is not worth the small amount of power gained. Without proper porting, the valves will not help at all. In an all out head, the floors of the exhaust ports need to be welded and the port raised. There is no short side radius to speak of even after porting and it hurts flow. As cast, there is a sharp 90 degree bend between the bottom of the port and the valve throat.
The head at the left has the earlier hemi combustion chamber. The heads at the right are late SPI heads.
The lower assembly is reasonably strong for moderate usage. Of course forged pistons are necessary for any serious power attempts or when running over 50 hp of NOS along with a performance ignition system. The bottom end could be made stronger with the use of aftermarket connecting rods. These are not cheap for this engine as they usually custom made. Adding high quality rod bolts will help the stock rods live longer in a higher rpm application. If going this far, the rods and pistons need to be made differently than the stock design specs. The rods are too short for his engine to make good power above 6500-7000 rpm. A shorter rod creates more of an angle with the bore centerline and increases friction and cylinder wall loading. A longer connecting rod and a piston with a higher piston pin location will be needed. A longer rod will also give the cylinder head more time to start flowing and works better for high rpm with a smaller port head like most CVH's.
This article was reproduced with permission from escortfocus.com.
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