4 in-line Intakes
This is what is commonly referred to as a 4 in-line manifold. It was standard on the 84 and early 85 (maybe) late 85. These are considered to be the less desirable intakes. As the runners are smaller than those on the 86 and every 2.3 manifold to follow.
4 Square Intakes
This is the more common and most favored 4 square style intake. The 86 Svo was equipped with this style of intake however it did not have the 2.3 markings on it. It was a smooth surface. This is a shot of intakes off an 88 T-Bird Turbo Coupe. These intakes are often used as upgrades for early Svo owners.
The 86 Intake
This 4 square intake was found in mid year 85.5 and 86 2.3T cars it is a very desirable upper intake manifold as it does not require a spacer to be made to clear the un-grooved valve cover. Also when rotated forward it sits higher and makes it easier to clear the alt. for intercooler piping
When /if upgrading the intake manifold from the 4 in-line to a 4 square manifold valve cover clearance is an issue. The best combination if you want to keep the stack valve cover is to use an 86 lower intake manifold out of an 86 Svo, Merkur, or TC, and the upper off of an 87-88 TC. Also with the lower 86 manifold acquire the fuel rail as it can be used on the Svo with no modifications. A second option is not using the stock valve cover and using an 87-88 TC or Merkur valve cover with the lower groove in the middle. If these options are not available you could use a 1/2" Birchwood spacer to help the 88 Turbo Coupe upper and lower intakes clear the valve cover. Purchase a sheet from a lumber store for $22, laid down the gasket used between the manifold and carefully cut the wood exactly to the gasket. Both manifolds were already ported to the gasket. Once finish put an epoxy around the edge to seal any air leaks or imperfections in the wood.
Time To Rotate
When using a front mount intercooler, it is opinioned by some to cut and rotate the upper intake manifold 90-100 degrees. With the intake rotated it allows less piping to be used in routing the intercooler tubes. In theory the less the air has to travel and the straighter it travels the more efficient it becomes.
Compare the Runners
These are two unported intake manifolds. The 4 in-line and 4 square. See for yourself the 4 square has a slightly larger advantage.