CA18DET Over the Top (CA16DE) Intake Manifold Install (Part 1)

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This is part 1 in a 2 part series that details the steps required to install an over the top intake manifold from a CA16DE motor onto the turbocharged CA18DET. This is part of the overhaul process for project 240sx (Project 240sx Overhaul Journal)


In a traditional intercooled system, the factory intake manifold on the CA18DET makes perfect sense. It faces the throttle body forward and works well for front, side and barrel style air/water intercooling. However, since the overhaul of project 240sx includes the addition of water injection as the only charge cooling method, a few changes unorthodox changes to the charge system can be made. Namely, by using water injection in place of the front mount intercooler, the traditional cold and hot pipe can be replaced by a single charge pipe along the shortest path possible. And by adding the CA16DE over the top intake manifold the shortest path possible runs directly over the motor. This manifold places the throttle body above the valve cover facing towards the exhaust side, opening up a path for a single charge pipe less than 2 feet in length. This not only reduces weight and complexity of the piping but it also eliminates the pressure drop associated with intercoolers, reduces lag and produces a more direct relationship between the turbo and engine. (Or in short, improves boost response all around.) Additionally, since the over the top manifold merges into a smaller, collector style chamber, the flow to the 4 intake runners should remain more uniform than is possible in the factory manifold.


Before part 2 which details the mods and install of the manifold, I want to take a moment to mention a few things. First, you could perform this mod to a factory boosted (7psi) CA18DET without intercooling or water injection. However, when you go to turn up the boost, something will need to be done to control detonation (water injection). Also, I modified the CA16DE upper intake manifold (very easy) to fit the lower manifold of the factory CA18DET unit. I did this because the CA18DET fuel rail will not bolt directly to the lower manifold on the CA16DE. Below are pics of the CA18DET Manifold and the CA16DE manifold as well as highlighted differences, port references and plugged ports with descriptions.

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