Intake/Exhaust ports

 

The original Ford flathead V8 has some unique ports. The intake and exhaust ports are partially obstructed by the large removable valve guides. In addition the outboard exhaust ports are very long as they travel the width of the block around the bores to exit in what we consider to be the normal areas. The center exhaust ports are forced to share a common outlet but also have the problem of no divider to separate the pulses between the adjacent cylinders. A passage to the intake manifold allows for carburetor heating. This arrangement, while suitable for the requirements of a stock production vehicle, leaves a lot to be desired in terms of raw performance. Another problem is the restrictive production factory exhaust manifolds

 

The ports in the new MCF block are a result of numerous flow tests. The problem of factory removable valve guide was resolved by resorting to a pressed in guide of a smaller diameter. This increases the cross sectional area of the port in a critical spot. The new port is d-shaped to further increase the cross sectional area and allow for a better shape leading to the short side radius. The valve size is increased to 1.7 diameter and it uses a smaller stem (7mm vs 11/32). The smaller stem takes up less area in the port and eliminates some weight from the valvetrain.

 

The exhaust port benefits even more from the use of the smaller diameter pressed in guide. The exhaust valve head remains at 1.5 and it uses the smaller valve stem diameter. Recent exhaust development confirms that this valve size should be more than adequate for most applications. For example, current Nascar engines use a 1.56 diameter exhaust valve to produce 800 hp in a naturally aspirated engine.

 

The intake and exhaust valves in the MCF block are using 30 degree valve seat angles for improved low to mid range flow and better seating. The MCF block does not use seat inserts for the exhaust valve. Inserts have been shown to increase valve temps by 100 degrees F. This could cause or further aggravate detonation.

 

The ports in the new MCF block are cut with a 3 angle cutter which qualifies the bowl at the same time. The design of the ports along with the above cutter eliminates 95% of the porting and cutting that was previously required on the original blocks.

 

The center exhaust ports on the new block are significantly different. The passage to the intake manifold has been eliminated and a divider now provides separation between the adjacent center cylinders.

 

Airflow continued:

 

The ports are only part of the flow path in the flathead V8. Two other important areas are the combustion chamber and the transfer area. The combustion chamber forms the shroud around the valve heads. This area can restrict flow if too small. If too large it gives away compression with nothing in return. The same thing can be said for the transfer area. It is crucial as it provides the same path for the intake charge and the exhaust during the 4 cycles of the engine. Old school thinking more or less relieved this area in a flat plane parallel to the deck surface.

Some of the factory relieved blocks were done in this manner and involved using a milling machine to remove a set amount of material from the deck surface between the valves and the cylinder bore. An optimal relief area includes a radius on the edge of the cylinder bore and a set amount of height between the block and the head in the transfer area. This area can be developed on a flow bench or dyno. Current multi axis machinery can now be programmed to properly cut this relief area saving countless hours of hand grooming. The transfer area in the cylinder head, once developed, can be incorporated into the cylinder head casting. The cylinder head is an intricate part of the flow path and can be very engine specific.

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