Can You run an S5 motor in an S4 by simply using an aftermarket ECU?
 

I have a 88 Turbo II and I was wondering if it would be possible to just throw in an S5 motor without having to swap front covers and crap. Yeah it is probably a stupid question but I was just wondering if there is an easier way to do this swap. Thanks for any positive input.

are you wanting to premix?

Not really but if I have to then so be it. I have to get more knowledge on that. I just want to be able to put the motor in and not do too much right now because I'm without a car and need the cheapest and or easiest way to get my car going again.

yes you can.wiring loom is a little different

You will have to rewire the cabin with S5 harness. The easiest way is S4 harness and S4 electronics I.E. AFM, BAC, Boost sensor and S4 TII Throttle Body due to TPS being different and a S4 TII or Vert ECU. Depending if your car has Low or Hi Imp injectors. 86-mid 87 S4 are low and late 87-88 S4 are Hi, you will have to short out the injector box plug and use the S5 injectors and clips due to S5 are Hi Imp. There are a few wires you have to pull on the ECU side so you can get the car to start and run with no problems. Search S4 to S5 Turbo. When you do the swap you will need a bigger fuel pump and dont redline stay under 6500 RMP Fuel Cut is NOT your friend, Thats how I blew my S5 JDM Swap

^I think a few people missed the "aftermarket ECU" part of the title. ;)

You could run nearly any engine with an aftermarket ECU.

As for the S5 swap... do it if you found one already. I figure though if you haven't, it's easier to find an S4 turbo motor than an S5 turbo motor.

Thanks Beefhole you bring up a very good point cause I overlooked The aftermarket part and the fact that it was already a S4 TII. Due to the thought of having all ready ran a stock JDM S5 engine which I blew on ignorance stepped up to a Built engine on a standalone. Some people normally say go for it to extract all the power you can out of it and I'm in the same boat but in the same thought unless your modding it I ask whats the point. So answer as Beefhole said and pointed out yes you can.

Yes the blocks are the same. The intakes, turbo, and omp is different on the outside of the engine. Ultimately if you have the choice between the two go with the S5. They have updated rotors in them and the turbo is better than the S4.

Holy thread resurection. Wonder if the OP is still active on this forum?