Classic Inlines
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Mesa, AZ 85210

Aluminum Cylinder Head - Development

The primary goal in designing and developing a new cylinder head, is the reduction of total ignition advance, while simultaneously increasing the air flow capabilities and chamber efficiency. By utilizing the best engineers and pattern makers, foundries and machinist, as well as the latest technology available, our goals were not only realized, but exceed.

In the past few years, other companies have produced aluminum cylinder heads for a limited market, such as an inline application, however their cylinder heads were designed for maximum performance with little or no considerations being given to cost. As a result, the cylinder heads were very expensive and beyond the reach of most potential buyers. Hence the demand for such a cylinder heads drops dramatically, just after the initial release date, and production is eventually terminated after a short run. It is our belief that a reasonably priced, high quality cylinder head, which maximizes the performance within the given design ("best bang for the buck"), will maintain a much higher demand long after the initial release date. In others words, unlike other companies we are in this for the long run, rather than the fast buck. The following article documents the entire design process and our results.

In the early stages, we spent several months doing extensive engineering studies which would assist us in making a decision as to the overall cylinder head design. This decision would be based on the initial design parameters, our desired performance goals, and our target price.

We began by establishing the design parameters and the performance goals for the new head, which are briefly outlined below.

Produce a cylinder head capable of 300+HP when naturally aspirated, and 500+HP when boosted.

Utilize the stock exhaust pattern and angle, allowing the use of current header designs.

Eliminate the siamese exhaust ports while maintaining the stock exhaust pattern and angle.

Incorporate the ability to utilize both shaft style rocker assemblies and stud mounted rockers.

Utilize stock valve cover design, allowing the use of chrome valve covers, or Classic Inlines new alloy valve cover.

Design and incorporate a new 4 barrel intake manifold with EFI and/or boosted induction options.

Achieve maximum HP and torque averages, while designing for economy and daily street usage.

Utilize existing 250-2V intake manifold designs, which are available for various carburetor options.

For more information you can read articles on the Design Parameters and Specifications, or you can view pictures in our Aluminum Head Photo Gallery. You can also read about the OZ250-2V head, or check out the history of the Australia Sixes.


Once the basic design was selected we needed to re-established the design parameters. Our primary concern was to produce a cylinder head which would meet most (or all) of our original design parameters, while maintaining the target price. Thus keeping our cylinder head affordable and within the budget of our customers.

To do this, we needed to keep the three main parameters in mind. First the new head needed to utilize existing exhaust port patterns, thus eliminating new header designs. We also wanted to split the 3rd and 4th ports to eliminate the need for a port divider. Next we wanted to maintain the stock OZ250-2V intake pattern so our aluminum cylinder head would accept the stock 2V intake, as well as any existing aftermarket intakes. This includes the triple SU and Webber manifolds. This will assist in reducing the overall cost of producing intake manifolds and gaskets, as well as satisfying the needs of our Australian customers. Last but not least, we wanted to maintain the stock valve cover and rocker arm designs, allowing our customers to use their existing rocker assemblies and valve covers. This would greatly reduce the customers initial out of pocket expense, thus making it more affordable.

While we obviously wanted to see improvements in the upper rpm ranges, our final goal was to increase low and mid range performance as much as possible. This would require designing intake ports large enough to flow the desired CFM's, yet small enough to maintain the velocity needed for excellent throttle response. We also needed a combustion chamber that was designed for maximum efficiency, as well as performance. If we could accomplish these goals, the end result would be a cylinder head that was well suited for daily drivers and weekend warriors alike, at an affordable price.

UPDATE 6-22-05

I spoke with the design engineer today and after doing months of research we both came to the same conclusion. While a cross-flow cylinder head was the most desirable, it was going to be to expensive to produce and keep within the targeted price. Hence the decision was made to base our new aluminum cylinder head on the old, but proven OZ250-2V design. With the decision made, we could finally move on to the next step, which is designing the intake ports and combustion chambers using computer simulation programs.

UPDATE 7-8-05

Not knowing the wet distribution pattern of the cast iron heads, we were uncertain of the gains we could expect. However flow testing the US and OZ heads, both wet and dry, would give us the answers. We also used the computer simulation programs to see what was going on inside the combustion chambers, which is really amazing stuff.

Our first step was to physically flow test both cylinder heads, to find their strengths and weaknesses. As expected, the Oz intake ports flowed considerably better than the US log heads, while the exhaust ports, which are of the same design, flowed nearly identical numbers. Combustion chamber efficiency was also very similar between the two heads, with a wet distribution pattern around fifty percent. Basically when the fuel/air mixture enters the combustion chamber it flows off to one side, filling less than half of the chamber, which results in huge losses of power. Both cylinder heads also required large amounts of total ignition advance to burn the fuel/air mixture, somewhat efficiently, during the power stoke. Since power output is decreased as ignition advance increases, the primary goal is to reduce the total ignition advance, while simultaneously increasing the CFM capabilities. The secondary goal is improving port velocity for maximum bottom end torque and performance.

With the flow testing under our belt, the next step is to redesign the intake ports and combustion chambers to obtain the best possible wet distribution pattern, or WDP. Most people, myself included, think the most important step is to increase the CFM capabilities, however this simply isn't true. The most important step in designing a new cylinder head is obtaining the best distribution pattern possible, even if it means sacrificing CFM. It doesn't do much good to increase flow, if the fuel/air mixture isn't distributed efficiently across the piston surface, and/or the total ignition timing remains unchanged. Therefore our goal was to increase WDP to 80%, if possible. This is done by modifying and reshaping the intake ports and/or combustion chambers. By increasing intake velocity, eliminating dead spots, manipulating swirl patterns, and playing with various valve combinations, we were able to improve the WDP considerably. While there are other means of doing so, like chamber styles, additional valves, valve placement, and so on, these options were not possible with our given design limitations.


UPDATE 9-14-05

After working on the new port and chamber designs for several weeks, we were finally ready to flow test them using a computer simulation program, the new intake port and combustion chambers achieved 100% distribution, which exceeded my expectations. This means the entire chamber is receiving the fuel/air mixture across the entire piston surface, which is outstanding. This alone translates into huge power gains over the cast iron heads, at all rpm ranges. While we are not sure yet, the total ignition timing could be reduced by as much as 10 degrees, or more. The compression ratios should also be able to be increase to 11.5 due to the excellent quench factors of the new chambers.

The new intake ports were flow tested for CFM rates. While were not ready to release the CFM rates at this point, we will say the new ports out flowed the old designs across the board, with the largest gains between .200 and .400, and ample gains at .500 to .600 lift. In other words, the new head is going to be a beast, when compared to the OZ250-2V, and incomparable to the US log head. Our next step, which begins next week, is to see what gains can be made to the exhaust ports. Our goal is to reach a minimum of 65% of the intake flow, with 80% being the ultimate goal. But is it possible within the limitations of the stock port locations?

UPDATE 11-8-05

I spoke to the engineer again today and the design work is finally completed. Again, he exceeded my hopes and expectations by bring the exhaust flow up to 73% of the intakes. This is outstanding and far exceeds our original aspirations.The design will work extremely well N/A or with boost, and is perfectly suited to a roots style blower. With the high velocity ports, fast burn chambers, excellent quench, 11.5 CR capability, 100% fuel distribution, and increase flow, this thing is going to be awesome.

We should be able to start the pattern work late next week and are shooting for an early to late spring release date. Once the first proto type is produced and we verify the flow numbers, I'll release more info on the flow numbers. The new head will also require an upgraded exhaust system due to the increase in flow and efficiency. A minimum of 2" dual exhaust pipes are recommended. Bottom end torque will come on fast and strong and will keep on going thru mid range into the upper RPM's. He NAILED the design and exceeded our original specs. I couldn't be more please with the results. I can't wait to dyno the first head, which will be video graphed, burned on a C/D, and offered to prospective buyers.

After going though all this, it has become very clear why it was so important to do all the work that we have done. Especially the wet flow and swirl testing. We had the option of simply reproducing the stock cast OZ250-2V head, but I felt it was crucial to take it to the next level and spend the money required to accomplish our goals, rather than settling for a half baked cylinder head. Hopefully you will all agree. I've heard that there are other companies out there looking at re-poping the cast head in aluminum, but I seriously doubt they will go to all the effort we have extended in this project. Remaking an existing design in aluminum is beneficial, but merely changing the port and/or chamber designs with out the research, is a gamble on the products end result, at your expense.

When we are ready to market the new head, we will provide all of the information you need to do a comparison to the current heads available. Nothing will be held back, we don't believe in hiding the information. We want you to know the facts, all of them, not just what we see fit to present. Why, simply because we know we will have the best cylinder head on the market. We want to show off our new motor at the same time. We have built a test engine (273ci) that will blow your socks off. Even now, the dyno runs are amazing, but we can't wait till the day comes when we can coupled it with the new head. Could be, the Vee-Eight guys will be swapping back to an inline six.

UPDATE 6-8-06

It's taken a long time to get to this point, but we have finally produced the first proto-type cylinder head, and flow tested it to see just how well we did with the new port designs. With high velocity ports, fast burn chambers, excellent quench and fuel distribution patterns, the new cylinder head should provide a performance level equal to, or better than that of most streetable small block vee-eight's.

We conducted flow test on the new aluminum head, and a stock cast 250-2V head, for comparison. It is easy to see the improvements in the flow, on both the intake and exhaust ports. Considering the exhaust ports were not change when they designed the 250-2V head, only the intake ports, the exhaust flow for the cast 250-2V heads and a stock US log head are exactly identical.

For our flow test we used 1.84/1.50 valves. The exhaust valves used for the flow test, were the closest (shelf item) valve available. However the production head will use a custom 1.55 with a 20 degree back angle. This custom size valve is being produced by SI Valves, exclusively for the new FSP/CI aluminum head. By using the larger exhaust valve, we should be able to increase the exhaust flow so that it exceeds the 170 mark, which is well past our original goal. 

The intake flow at 100-200 was slightly lower than the cast head, but it really comes on just after the .200 mark. Note that the cast head saw no increase in flow after .400 lift, thus limiting top end horsepower. Given the excellent torque output of the small six at low rpm's, we were more than willing to trade a little low end flow for the substantial increases achieved in the mid and upper ranges. However, with the new high velocity ports, we doubt there will be any decrease in low end power, in fact we expect just the opposite. To our knowledge, the best intake flow numbers using a log head were around 130cfm, but that has not been confirmed.

Ford Inline Six - Aluminum Cylinder Head
Valve Lift / Flow
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
Valve Lift / Flow
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

As seen in the picture graphs below, the new aluminum head flows nearly the same cfm as two notable V8 cylinder heads, which are able to utilize bigger valves due to their larger bores. However, the flow improvements over the OZ cast iron head and a ported US log head are evident. It is also easy to see the substantial gains in the exhaust flow, when compared to the US log or OZ cast iron heads.

The exhaust ports show a substantial increase in cfm across the board, resulting in a excellent flow ratio through out the entire rpm range. This is difficult to achieve in any cylinder head design, and was a major fault of both the US log and the OZ250-2V heads. Increases in excess of 50 percent are realized in the high lift ranges, making it especially well suited for turbo charging, as well as supercharging. Needless to say, we are very pleased with the results.

UPDATE 8-17-06

The second proto type cylinder head arrived, and is pictured below. We still have some minor issues to deal with, as the placement of the exhaust ports is a bit high and doesn't allow enough clearance between the intake and exhaust flanges. Therefore the patterns need to be sent back to the pattern makers for the modification. They will lower the exhaust ports fifty thousands and add a bit more material to the face, to achieve the necessary clearance between the exhaust and intake flanges.

While they have the pattern, the third proto type will also see the addition of injector pads on the top of the intake runners. These will need to be machined by the customer if injectors are to be installed, for either fuel injection or NOS. If injectors are not used, or installed in the intake manifold, the pads could be used for multi-carb linkage, throttle cable anchor points, or other needs.

Raising the intake runners to allow room for the new port designs, also required raising the stud pads. This modification requires a custom ARP stud/bolt set, with the studs or bolts being approximately one inch longer on the intake side only. It also required raising the valve cover walls to achieve adequate clearance between bolt head, or nuts (studs), and the bottom rim of the valve cover. However it will not effect the use of stock valve covers, and provides additional clearance for high ratio rocker assemblies.

UPDATE 12-15-06

Producing three proto type heads allowed us an opportunity to do visual inspections and mock ups on each. And in each case, we discovered small issues that needed to be dealt with before proceeding to the next step. All these changes take time, in fact several months, however we feel we finally have all the issues handled and are now ready to produce a small batch of cylinder heads for testing. A dozen heads will be produced and shipped to various FordSix forum members so they can be installed and tested in real world conditions. We will also be running our own motor on a dyno for at least one hundred hours. Once the heads have been tested and we are certain no other changes need to be made, we will begin the production run. Once the approval is given, it will take approximately six to eight weeks to cast and machine the production heads, which will result in a release date sometime in late February or early March.

While this is several months behind schedule, we needed to be certain all the details were correct before investing thousands of dollars in a production run. Hopefully our customers understand our dedication to perfection and our desire to produce the best cylinder head possible. As I've stated many times, we simply refuse to take shortcuts or look for cheaper methods of production, which would result in an inferior product.

In the picture below, the aluminum head is mocked up with a header, a triple SU intake, and a raw valve cover. Notice the injector pads on top of the intake runners, which need to be machined by the customer. They can be utilized for injectors, either for fuel injection or NOS, or as pads for multiple carb linkage, throttle cable anchorage, etc.

click images for larger view

We will be offering various intakes, the first which will be suited for a Holley 4V carb. It will also allow a single 2V, or twin Weber's, to be fitted by using an appropriate adaptor. Other intakes will include a 3xWeber, an EFI plenum style intake with a single throttle body. For those enthusiast that are interested in going beyond natural aspiration, we will be developing turbo and supercharger kits, which will include an inter-cooler when applicable. For maximum performance gains and no guess work, we will offer complete systems with matched cams. You simply choose the proper kit based on the type of driving you do, and the performance desired. Whether its off road, street, all out performance, we will have a package that will fit your needs.

UPDATE 12-28-06

Our new four barrel intake is taking shape, as the core boxes have been completed and they are starting on the molds after the holidays. We also had a custom aluminum full race intake fabricated by Hogan Manifolds. Notice the large plenum chamber under the carb, which makes this intake unsuitable for street use with naturally aspirated induction. However, it will do wonders for a turbo charged, high rpm, drag motor.

UPDATE 09-09-07

It's been several months since we posted an update, so here we go. We received a dozen proto type cylinder heads earlier this year (07) and sent a few out to forum members for field testing. Their comments are posted in the Dyno & Field Testing section. We also installed one on McLearran Racing's turbo charged 63 Falcon, which is sponsored by Classic Inlines. In short, the average ET's with the modified log head were in the mid to low twelve's. With an OZ 250-2V cast iron head, the times dropped to the mid elevens. The first race with the aluminum head, we dipped into the high tens, with a 10.95 run at 124mph.

We took the Falcon to Portland in August for the Dearborn Classics West Coast Ford Championships, only to blow the motor on Saturday turing a test and tune section. However, we were getting it dialed in, running low elevens, and were quite sure the Falcon would have ran its best ET's to date that Sunday. But it was not to be.

We're now in the process of rebuilding the motor, which had a cracked wall in the number five cylinder. We had planned for a cam swap in the old motor, so the new block will get a solid lifter 292 cam, instead of the old H274. We were hopping to have it ready for the Speedworld race in late September, but it looks like it won't be ready in time. However we will be racing in Tucson late October, for the popular TV show PINKS, and hope to run mid tens or better.

Last week we received good news and headed down to LA to pick up the first two proto type 2V/4V intake manifolds. We spent one morning with the pattern maker, going over the intake, plans for the triple Weber intake, and worked on a carb adaptor for the proto types. I wanted to try using a phenolic spacer as an adaptor, rather than aluminum, but wasn't sure if it would be strong enough for daily use. However, after machining and mounting a spacer, we both determined it should work just fine. We may switch to a pressure molded phenolic spacer for the production units, but still need to do a little research to make sure they will work OK.

The new intakes were based on the old cast iron OZ 2V intake, but have been modified to suit our needs. The new intake runners reduce in size over the length of the runners, unlike their OZ counterparts, which will result in increase port velocity for better throttle response at lower rpm's. We also made the intake universal, so the carb adaptors can be mounted in any position, thus allowing the carb's to be mounted parallel or perpendicular to the crank, depending on the application. We can also make an adaptor for mounting a single throttle body for fuel injection applications.

The proto type intakes do not have a water box, as they are still working on the molds. However they will be cast into the production intakes and will utilize threaded nipples. While the old cast OZ 2V intakes bolt up to our aluminum head, the intake ports do not line up as they should. This is result of moving both the intake and exhaust ports during the design stage, to optimize the air flow numbers, as well as making the new ports slightly smaller for improved velocity. The mismatch results in an 1/8-3/16" crescent shape ridge in each of the intake runners, which os obviously creating massive amounts of turbulence. Therefore when we install a proto type intake on one of the test motors, we should see a definite improvement in performance.

All in all, we are very pleased with the new intakes and look forward to receiving the production manifolds in a month or two. While the old cast 2V intakes are interchangeable with our new intakes, we should point out they will need to be port matched for the best results and optimum performance gains. Make sure to read the specification page, which includes a virtual dyno test with various engine configurations.

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