Head for Numbers

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POSTED ON October 30, 2017
A new Cleveland cylinder head is being developed right here in WA to produce big power and excellent torque.

The choice of performance cylinder heads has exploded in the past 10 years and, in effect, this new version of the Cleveland cylinder head adds to an already extensive range of smallblock Ford heads. This head differs because it is targeted at the very popular 427-434 cubic-inch capacities and is designed for moderate to high compression ratios (11.1 and up), together with high torque and horsepower outputs and moderate revs of 6500-7000rpm.

These new cylinder heads are an adaptation of an LSX 434-cube Engine Masters motor that Leon of A1 Hi Performance had studied. In 2009 it produced 750hp at 6500rpm and 635lbs/ft torque at 5000rpm on unleaded fuel. The study of this LSX engine allowed Leon to transfer the knowledge gained to a Ford Cleveland style cylinder head.

The Kaase style combustion chamber has been retained at 42cc as this enables a fast burn and limits negative torque in the engine (negative torque is created when a cylinder that has already fired and is pushing the piston down the bore and is, in turn, rotating the crankshaft. This piston also has to overcome the rising cylinder pressure of the next cylinder in line building pressure before TDC due to advanced ignition timing).

To obtain compression ratios of 11-11.5:1 (using the small 42cc combustion chambers) either a reverse dome or dished piston is used to reduce compression whilst maintaining a fast burn rate.

The next part of the design incorporates the valve seat where the top cut becomes part of the head’s chamber. Below the top cut, multiple angles are used to transition the fuel/air mixture flow from the bowl into the chamber. These angles are tuned to optimise airflow at particular valve lifts and can also be optimised to reduce reversion, which may be present in some engine combinations.

Above the seat the bowl, short turn and throat design sets up the behaviour and velocity of the air mixture as it exits past the valve seat and into the combustion chamber. An example of this is where the port to valve angle 90°. In this case the intake air speed over the short turn will be faster than the intake air speed of a port to valve angle of only 60°. So, to counter this a wider short turn can be used to slow down the air speed; increasing the throat and bowl area will also slow the air speed (not withstanding some loss of velocity at low engine speed). By raising the port and spreading the radius, the short turn is made longer therefore allows a higher average air speed and localised mixture before the incoming air becomes turbulent.

Featuring a 259cc intake runner and a 145cc exhaust runner – these new heads are designed for 427/434 CID smallblock Ford combinations revving to 7000rpm.

Lastly, the cross-sectional area of the port, which is a major controller of how the air speed is set, must be considered. Setting the cross-sectional area is done to optimise a given engine size to a given rpm range. A 408 cubic-inch engine could make peak power at around 7000rpm with a minimum port restriction of 2.4 square-inches, however a 454 cubic-inch engine with the same cross-sectional area will reduce this peak power point to around 6000rpm.

Calculations regarding cross-sectional area are compounded by the shape of the port, as square ports do not tend to flow in the corners, so a port needs to be larger to compensate. That is why this Ford port is (as are most late model heads) of an oval design to optimise the space available. This new Cleveland cylinder head optimises this theory with a minimum cross-sectional area of just over 2.6 square-inches and intake air flow of 300cfm at only .450-inch of valve lift. The port flows over 350cfm at .550-inch lift and over 380cfm at .650-inch lift. This continues to 389cfm at .900-inch lift and shows that these heads do not fall over, even at lifts far in excess of most street or even competition engines.

Port velocity is also good at low lifts and is not excessive at high lifts while exhaust flow of over 215cfm at .500-inch lift, combined with quiet flow characteristics will, with the right valve shapes, produce excellent torque over a wide range – together with high horsepower at moderate compression ratios.

As we speak new manifold combinations are in the test mode and will be available together with these heads. Perth Street Car will be the first to show the final dyno results of an engine built to test the new head and manifold combination.

With a 42cc combustion chamber and three intake seat angles (45°, 50° and 55°) and two exhaust seat angles (45° and 55°) excellent flow and velocity result in an exceptional street/strip head.

Intake Port Flow – (28-inches H2O)
Valve Diameter: 2.19-inch. Throat Diameter: 1.9975-inch (91%)
Exhaust Port Flow – (28-inches H2O)
Valve Diameter: 1.650-inch. Throat Diameter: 1.434-inch (86.9%)

 


From old 2V Cleveland (right) to early V8 Supercar (left) these port moulds show a remarkable evolution in design.


A1’s 259cc port (left) note that the short turn radius is longer and more gentle than the 283cc Kaase port (right).


The importance of valve seat, chamber transition and the coefficient of discharge characteristics become critical. Valve sizes are 2.19-inch and 1.65-inch.


The intake port is .030-inch taller than previous versions and the exhaust port requires a slightly different header plate available from A1.

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