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The cylinder head is rough ported by Hasselgren and finished by Technosquare. A late post 1988 4AG head is used as it has a smaller but better flowing intake port. The intake and exhaust ports have smoothed short side radius, moved back port splitters and raised flattened roofs. The combustion chamber is unshrouded in the area by the valves and the deck surface is fine milled and lapped on a surface plate for better sealing.
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The combustion chamber valve unshrouding is shown here, you can see how the edge of the combustion chamber is moved back from the valve and valve seat. This really helps flow as the valve starts to open and close. A 3 angle valve job is used with the top 30 degree cut blended into the combustion chamber and the 70 degree throat cut blended into the seat and port wall. The 45 seat is kept to around 1 mm in width on the intake side and 1.2 mm on the exhaust side.
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The intake port starts with the valve bowl. The valve seats are opened up for the bigger valves and opened though to the valve bowl. The valves are supported by bronze TRD valve guides. The entrance to the bowl is opened up and material is mostly removed at the port roof. The short side radius is rounded.
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You can see the extent of roof flattening in the intake port here. This gives the best flow with the least volume for good port flow velocity. This gives the best throttle response and widest power band. The port splitter is moved back to give more flow area without increasing volume much. The EGR bosses in the roof of the intake ports are plugged.
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