Classic Inlines
603 W Pecos Ave
Mesa, AZ 85210


 
Aluminum Cylinder Head - Overview

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.


OZ250-2V vrs. Cross-flow

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.


Advantages and Specifications

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.

Additional Flow Test Results

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.


Ford Inline Six - Aluminum Cylinder Head
(144/170/200/221/250ci)
Intake
Valve Lift / Flow
.100
.200
.300
.400
.500
.600
US Log
45 cfm
87 cfm
108 cfm
119 cfm
124 cfm
127 cfm
OZ 250
63 cfm
101 cfm
133 cfm
155 cfm
156 cfm
156 cfm
CI Alum
52 cfm
99 cfm
143 cfm
180 cfm
201 cfm
210 cfm
Ported CI
55 cfm
103 cfm
159 cfm
196 cfm
223 cfm
231 cfm
Exhaust
Valve Lift / Flow
.100
.200
.300
.400
.500
.600
US Log
36 cfm
68 cfm
91 cfm
98 cfm
103 cfm
105 cfm
OZ 250
36 cfm
68 cfm
91 cfm
98 cfm
103 cfm
105 cfm
CI Alum
40 cfm
79 cfm
111 cfm
144 cfm
164 cfm
174 cfm
Ported CI
44 cfm
87 cfm
122 cfm
159 cfm
179 cfm
184 cfm

Flow Charts




Estimated Performance Gains

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.

Engine Build Specs - Naturally Aspirated- 250ci (+.040)
Head
Cam
Valves
C/R
Induction
Exhaust
Rockers
Stock Log
H-64/64-112
165/138
8.5
1V-185
Header
1.50 Adj
Mod Log
H-64/74-112
175/150
9.5
2V-500
Header
1.50 Adj
OZ250
H-64/74-112
175/150
9.5
2V-500
Header
1.50 Adj
CI-500
H-64/74-112
184/150
9.5
2V-500
Header
1.50 Adj
CI-600
S-78/78-110
184/150
10.0
4V-600
Header
1.60 Tip
CI-EFI
S-78/78-110
184/150
10.5
TBI/EFI
Open H
1.65 Roll


Estimated Performance Comparisons
Engine
Torque
Horse Power
1/4 Mile
Peak
RPM
Peak
RPM
ET
MPH
Stock Log
176
3000
133
4500
18.01
74.23
Mod Log
203
3500
179
5000
16.27
82.78
OZ250
217
3750
202
5250
15.63
86.16
CI-500
245
3750
237
5500
14.82
90.89
CI-600
312
4000
302
5750
13.67
98.55
CI-EFI
335
4250
351
6000
12.99
103.60












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