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Aluminum Cylinder Head - Overview |
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This page will give you a brief overview of our new aluminum cylinder head for the Ford small inline sixes (144/170/200/250ci). We will touch on our reasons for choosing the OZ250-2V platform (rather than a cross-flow) as well as the advantages, the flow test results, and estimated performance gains. Eventually, we will add the results and comments from customer field testing and dyno results, once they have been provided.
The advantages of designing a our new aluminum cylinder head based on the US/OZ head, rather than a cross-flow format, basically came down to cost. A cross-flow format would have required designing, developing, and purchasing custom parts, all adding to the overall cost of a new cylinder head. Whilst the 250-2V design allowed the ability to utilize existing parts, whether stock or aftermarket. This means your existing valve train components, (rocker assembly), valve covers, and headers are compatible with our new aluminum head, which saves you money. Even though a cross-flow design would have resulted in significantly higher gains in air flow and overall performance, we felt the added cost of designing, developing, and producing the additional parts required, would have been prohibitive for most of our customers. By the time you add the expense of new rocker assemblies (even if shelf items), valve covers, headers, and a new or modified distributor, you could easily double or even triple the end cost to the consumer. Therefore we designed our new cylinder head around the OZ-250-2V platform. The end result is an affordable cylinder head which offers a substantial increase in air flow and performance when compared to the integral log head or the OZ250-2V head. For more information and complete details, read the Design Parameters and Development pages. You can also read about the OZ250-2V head, and/or visit our Aluminum Cylinder Head Photo Gallery which contains photos of the cylinder head, intake manifolds, various induction setups, and customer installs.
Contrary to popular belief, the primary goal in designing an efficient cylinder head, is to reduce the total ignition advance. Increasing the air flow, or cfm, is the secondary goal. A well designed cylinder head will accomplish both task, resulting in maximum power and performance gains, while maintaining reliability and economic efficiency. Not knowing where we stood with the cast iron heads, our first task was to flow test the US and OZ heads, both wet and dry. It was immediately apparent that the chambers were inadequate in both heads, yielding poor fuel distribution and quench. This also explains why both heads respond so well to boost. Not only is the cfm increased, the fuel distribution is enhanced when under boost. These issues have been resolved in our new aluminum head, which offers excellent quench and fuel distribution characteristics. The exhaust ports and the high velocity intake ports, which are slightly smaller than those on the OZ head, were also elevated to allow a more gradual port radius. These improvements in the port and chamber designs allowed us not only to reach our original goals, but to exceed them.
A good street/strip cylinder head has an intake to exhaust ratio of approximately 75%. By using a 1.84 intake and 1.500 exhaust valves, we achieved an average ratio of 75-79% at all valve lifts, thus making our aluminum cylinder head well suited for naturally aspirated as well as boosted applications. The fuel distribution was raised from 40-50 percent, to 80-90 percent by applying a new high swirl chamber design and high velocity intake ports. The chart and graphs below show the airflow (CFM) as compared to a US log head, the OZ250-2V head, and two popular V8 aftermarket cylinder heads. The exhaust graph shows a substantial increase in airflow over both the US and OZ heads, which were nearly identical. While we did initial flow testing on our proto type heads we decided to do additional flow test with our new intake manifold attached, as well as an exhaust header, to see what differences might be realized. The following graph is a result of those test. To our surprise, we actually saw an improvement of 4-5 cfm on both the intake and exhaust ports.
Flow Charts
While we are uncertain of the precise gains until field or dyno test can be completed, we do expect substantial increases in performance. Therefore we ran six engine builds on a dyno program using the various flow numbers. The results are posted in the charts below. These are not actual numbers, and should only be used for estimated comparisons. A total vehicle and driver weight of 3200 lbs was used to figure ET's and MPH.
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