The Regular Brumfield Head and its comparatively odd compression ratio of 5.9 to 1 was designed specifically to give maximum performance within the limits of properly adjusted, original Ford type babbitt bearings. Our goal was to produce a cast iron cylinder head with an original stock appearance that would be most appealing to the greatest number of Model "A" enthusiasts and yield excellent results throughout the normal r.p.m. range. The head's construction is similar to Ford's original (large B) high compression police head, only better, with changes in the combustion chamber's configuration and volume which improved the air flow in the valve area, increased the power, and the compression ratio.
Any increase in the compression ratio of a normally aspirated engine will increase the cylinder pressure, but maximum cylinder pressure won't be obtained unless the incoming and outgoing air keep up with the draw and the expulsion. In other words, air flow restrictions in a high compression head's design can lower the filled volume of the cylinder resulting in reduced compression pressure that may not be in proportion to the higher compression ratio. Therefore, compression and air flow must work together for maximum results. The Regular Brumfield Head achieves this compression and air flow harmony by having the correct radii in the valve area, over and toward the piston. By having the correct radius, the valves have more room to breathe which increases the air flow. The actual increase in the compression ratio itself, which coincides with the air flow, occurs as a result of the reduction of the overall volume of the chamber. More compression is also gained as the flame front traverses the charge and the expanding, burning gases further compress the unburned mixture ahead of the flame.
On the Regular Brumfield Head, the correct radii also has a direct effect on the turbulence. Turbulence is the spinning action of the mixture as it is being compressed and it is created when the air flow follows the shape of the combustion chamber. The result is a more uniform mixture that burns faster and allows the charge to be consumed to a greater extent. Moreover, the movement of the swirling air helps to reduce detonation by keeping the chamber temperature below the detonating point. The effect is a smooth burning, non-detonating flame which increases the power of the engine. As an added benefit, the formation of carbon on the Brumfield heads is delayed because the proper amount of turbulent air flow allows the maximum amount of the mixture to be vaporized and completely burned. Many of our customers have noticed this and refer to it as a "slick spot" in the valve area when describing how clean the chambers stay.
The circular counterbore above the piston on the Brumfield heads is most important, and it is another area which intensely affects the turbulence. The counterbore area serves as the quench area, sometimes referred to as the "squish" area. The quench area includes the surface area and the distance between the top of the piston and the bottom of the head in the top dead center position. The thickness of a compressed head gasket adds to the distance. The purpose of the quench area is to drive the compressed mixture toward the combustion chamber at great speed. As a result, turbulence is increased, and the closer the piston is to the head, the greater the amount produced.
The optimum quench height varies from one engine to the next with .040" being a good average. However, on the Brumfield heads, the large surface area above the piston in conjunction with the chamber's particular radius can cause too much turbulence with a close quench. There is about 75% flat surface area above the piston on the Regular Brumfield Head and even more on the Brumfield Super Head. Turbulence increases the flame speed, and too much turbulence can make the fuel burn erratic. With increased flame speed, if the timing is not sufficiently retarded, too much of the burning process will occur early when the piston is in its top dead center position. At that position, the piston is static for an instant and resisting downward motion. While the piston is temporarily static, the heat of the flame is increasing the chamber temperature which will promote detonation. Any great rise in heat also necessitates the need to further retard the timing because the heat increase makes the mixture burn even faster.
Stated more simply, a close quench on the Brumfield heads can cause erratic burning and detonation that may not be eliminated with timing adjustments. Consequently, the quench distance will vary from .140" to .160" depending on the thickness of the gasket used and a flush deck height. At the same time, detonation can also occur if the quench distance is set too far, especially in higher compression ratio engines such as 9.5 to 1, etc. The higher chamber temperature of these engines needs the cooling effect of the close quench turbulence. However, with the Brumfield heads, this is not the case. Since the compression is low (as compared to 9.5 to 1, etc.), the loss of turbulence from a greater quench distance still does not promote detonation and provides enough turbulence for a smooth running engine. Moreover, a greater quench distance allows the Brumfield heads to accommodate the varying deck heights caused by multiple or excessive block resurfacing.
One of our highest priorities when we were developing the Regular Brumfield Head was to make sure that the compression pressure was not too much for the old Ford to handle. One of our first customers kept saying, "Those old rods can't take it!" Now, after several years and many miles of trouble free service, that same customer is singing us a different tune! However, we still cannot make any bearing guarantees because we have no control over the condition of a customer's engine. To understand exactly, we conducted several tests with different compression ratios to determine the limits of properly adjusted, sound, original Ford type babbitt under severe loads. These particular tests were conducted as "street" tests because a dynamometer does not simulate the exact bumps, strains and irregularities encountered on the road. During each test, the engine was allowed to reach the maximum r.p.m. possible and held there for long periods. The results of these tests are the reason that the Regular Brumfield Head has a comparatively odd compression ratio of 5.9 to 1. At that ratio, our inspections never revealed any damage to the bearings regardless of the pressure applied. Since that time, we have seen this fact appreciated because babbitt bearing failure has been the biggest concern of our customers when increasing the power of their engines, since day one (1986). However, as the ratios increased, inspections revealed that the effects on the babbitt varied all the way to the early stages of flattening or mushing out the side of the bearing.
When running a higher compression head on the Model A/B block, there is not as much room for error and careless installation as with the stock head. There are only 14, 7/16" studs and nuts, and that number and size were designed for a stock head's compression ratio. With a higher compression head, they have to work much harder to hold the extra pressure. For that reason, new studs and new nuts no less than Grade 5 should be used and used only one time. That may sound like a waste to some people, but the studs and nuts lose a certain amount of their clamp after the first time they are used, especially when torqued to our recommended amount of 60 to 65 ft.-lb. In addition, the gasket surfaces should be flat within .003". Gasket surfaces that are not flat and insufficient clamp are the primary reasons for head gasket failure on any cylinder head. Moreover, gasket surfaces should be completely, physically clean. On the Brumfield heads, to ensure more accurate torque, we recommend that the contacting surfaces on the stud bosses should be left unpainted, smooth and oiled. We also machine the bottom gasket surface to a finish with slight roughness instead of perfectly smooth to aid in the head's grip on the gasket.
The best gasket to use with the Regular Brumfield Head is the Fel-Pro 7013 C R3 copper-clad. They are the most widely available, and even though they are made for the original stock head, they work best because the Regular Brumfield Head is made as wide as possible in the valve area for maximum breathing. That's part of the secret of the performance.
In conclusion, if today's gasoline had been available at the time of the Model A's manufacture, Ford would have probably lost sales with a compression ratio of only 4.22 to 1. However, it was a good decision at the time because nobody wants a poor running engine full of knocks and pings. Fortunately, the desire for better performance created a need for better gas, and at the risk of sounding like a salesman, Model A'ers who are not running a Brumfield high compression head just don't realize what a difference they make in performance and driving pleasure. There's nothing like it. Try one and you'll see, guaranteed!