mikevr007

I've searched and can't find anything that specifically answers my question.

I want to drop in an S5 into my son's 1986 RX7. We have the engine, the ECU, the engine harness, and the proper flywheel. What else do I need to put the S5 in as is? I do not want to take parts off the S4, I don't want to use the S4 ECU. Please don't tell me it will be expensive, please don't tell me it's not worth it, etc. All I need to know is what else I need. I'm thinking all I need is the harness that enters through the fire wall and maybe the gauge cluster. ??????
We're really pressed for time!
Thanks!
Mike

SOIA

NA- Turbo?
Turbo-Turbo?
NA-NA?

you will have to replace the interior harness as well if you want to use the S5 ecu, I can help you out more after you specify which conversion you are doing.

SOIA

mikevr007

NA everywhere.

bingoboy

when you say engine, you mean the longblock with everything including stuff like sensors and the air flow meter etc.?

mikevr007

If you mean any sensor that's part of the motor, then yes. The S5 is a complete motor. I'm not sure if I have the air flow meter. I think I do, but if I don't I can get it. If it's part of the throttle body then I do. If it's part of the air box and/or tube then I may not.

SOIA

With some modification you can get it to work with the S4 computer + harness, you will just need RPM switches for the VDI and aux ports. If you really want to use the S5 ecu the interior harness will have to be replaced as well and probably some interior components as well.
Here is my ordeal, it may be of some help

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s4-s5-engine-swap-327921/

mikevr007

Ok, here's my thought process...
Other than the sensors on the engine (I doubt any of them were changed in '89 and even if they were, they still serve the same function), you have an O2 sensor, which probably isn't different either. The ECU controls air, fuel, and spark using sensors to adjust as necessary. What component(s) "inside" would have to be replaced? If it's just a matter of wiring, I can adapt the harnesses.
The reason I want to use the S5 ECU is that I know that the S5 has a higher compression ratio so I know that the air, fuel, and spark programming is going to be different (read better) than the S4 ECU and give me a little bit better performance all around.
Anyway...it can't be that difficult...this isn't rocket science.

Aesop Rock

im going to say wait for RETed or do a search for people who did this similar swap, i know it has been previously.

mikevr007

Ok...again...
I've read through the links.
I can't believe what I'm reading. I know there are people out there that think you have to change the front cover and the fuel rails and you have to use the S4 ECU....well...mazda sure didn't do that in 1989....SOOOOO there has got to be a way to do it now.....don't ya think?

Aesop Rock

Yes there is a way, however im not nearly expierienced enough with electircal to tell you, PM RETed, he will answer you in the most straightfoward way possible, he know his stuff.

mikevr007

Well....I guess I'll do what I think will work and see what happens.
I'll let yall know what happens.
In the mean time, if anyone that has actually bolted an S5 motor and ECU, complete, and un-modified, into an S4 chassis, please donate some experienced commentary.
Thanks for all the input!
Mike

Aesop Rock

now that ua one thing that will work

mikevr007

Ok...from what I have learned, as long as I have the S5 ECU, the S5 flywheel, and the S5 engine harness, everything will work great. The only thing I will need that I don't have is the inside harness connector that plugs into the ECU. Once I get that and splice it in place of the old ECU connector I'll be done. Having the S5 ECU and the engine harness to go with it is the key.
If ANYONE wishes to disagree please do, but don't just disagree, please explain why you disagree.
Thanks!
Mike

Aesop Rock

what about the rest of the cars electronics? have you searched on mays to over come those differences?