Converting an S4 to an S5 is strongly discouraged (unless you have a standalone). The troubles outweigh the benefits that are easily solved on an S4.

What is a N/A to TII conversion exactly?

Take an RX-7 2nd generation with a naturelle aspirated engine, and transplant the same model, but with a turbo.

This article will outline the parameters to respect, the tools and parts needed for you to do your own conversion (n/a to TII) from A to Z.

1- Find the parts!

Since you can never avoid shipping delays and budgetary surprises, it is best to have ALL the necessary parts before even starting to undo your first bolt. This will avoid your precious project going to recycling due to it being a perpetually incomplete project.

Here is a list of what you’ll need:

-Complete engine with intercooler (unless using a front mount)
-USDM wiring harness (The N/A harness can work)
-ECU Turbo (Preferably USDM. Jspec works, but we advise against it as they are tuned for 98 octane)
-Turbo boost sensor.
-Turbo throttle cable. 87-91 are not interchangeable
-Turbo brake boost vacuum pipe (or you can make a custom one)
-Stock Turbo fuel pump (87-91 turbo pumps are the same, but the bracket is not. Or buy a Walbro 255. (recommended for more flexible fuel intake) A fuel pump re-wire is recommended to ensure a constant voltage on the pump, in order to not run too lean

-Stock turbo intake duct with blow-off valve (this is typically already installed on the engine). The 87-88 TID is smaller than the 89-91, but they are interchangeable. The BOV is also a little different, but both can be used.
-Stock TII precat/downpipe and midpipe. (or aftermarket/custom if equivalent)
-TII hood with scoop (unless using a front mount as of day-1)
-Turbo air flow meter
-Aftermarket boost gauge is recommended. Even though the owners of 89-91’s can install the TII cluster, the boost gauge will work, but will not be as reliable. The 87-88 cluster is not adaptable as the wiring harnesses are not the same.
-TII tranny + flywheel. An aftermarket clutch and pressure plate is recommended. (Ex: ACT are often less expensive than OEM, and don’t forget, best to change it now and avoid extra labour charges if ever it fails after 6 months.) *optional, you can use the n/a transmission but it will likely not last.
-TII Driveshaft. You will need to customize your driveshaft in a specialized shop like Derwin Performance. You bring both TII and n/a shafts and tell them you need the N/A flange on the TII driveshaft.

*Only for 87-88 turbo (S4) knock control

  • Little grey box that plugs into the harness on the passenger side of the side-dashboard.

    Now, disassemble everything, mark your hoses and vacuums with marking tape (easier to write on and remove versus tie-wrapped tags)

    You’ll need a good ratchet set, long-nose pliers, vaseline for the hoses and o-rings, maybe a torch, 10’ of red and black wire 18 and 12, vacuum kit (to do things properly) and a pair of strong arms. Don’t forget that you’ll need a 54mm key if you plan to remove the flywheel.

    Exceptions for S4

  • -On the 87-88, you’ll have some re-wiring to do for the alternator. The change is made in the joint where the cassis and engine harnesses meet.
    -The temperature gauge will not work. It will indicate 150C 5 seconds after the car has started. It is best to purchase a new aftermarket water temperate gauge. Or you can rewire it. You’ll need to locate for receiving wire for your N/A temp gauge (Yellow/Red) cut it leaving a good 6”. Then find the same wire in the TII harness and connect it. We recommend connecting it when everything is installed in the car.

-It is possible to have a high or low impedance harness, and with or without resistor packs, depending on the year of manufacture of your S4. We can note the differences as follows:

Plugs for the injectors:
-Square off-center plug is High impedance for the injectors. Make sure you have HIGH impedance injectors.

-Oval ON-center plugs is Low impedance. Make sure you have LOW impedance injectors.
For low-impedance harnesses, some come with a resistor pack and others don’t. To know, check near the AFM at the end, if there is a large beige plug  with 6 entries, you need a resistor pack. The resistor pack can be fixed to the bottom of the air filter box.

Personal advice:
•Clean the injectors, half of the time, they are jammed! Remember the engine has likely not been run in a while!
•Use new gaskets, silicone is not reliable.
•Run premix
•Take your time, and spend the money to do it right. Cheap will bite you in the ass!!