Well just bought an S5 RX-7 that was victim of engine fire. I got a spare S4 motor with it, and full harness too.

Question is, if I have the full harness and ecu, will this be plug and play?

I'm guessing not since maybe cluster and all that stuff use the S5 harness.

The S5 harness melted by the way.

 

Harnesses are different so are all the electronics.

Many things are different and will need to be changed to adapt, but it is possible though not recommended..

The very best would be putting an s5 engine into an s4.

You'll be losing power by putting in the earlier engine since its not designed for the same ignition and fuel maps, s4 redline in na is 7000-8000rpm, s5 is 8000-8600rpm.

S4 has different intake manifolds (no variable dynamic intake), mechanical oil metering pump(rather than electronic), lower compression, heavier rotors, etc.

 

Basically what he said. Finding a new set of used S5 harnesses would be the easiest way to go.

If you do go to S4, then the best way to do this is to simplify the emissions harness to the point where it is totally standalone and requires only 12V and ground to operate. Sort of like if you were installing the engine into another car. But you'll need all S4 engine electronics and you'll need to add the missing parts of the harness to your new emissions harness (coil wiring, CAS, a few other bits). Not really too hard if you can follow the diagrams in the Haynes manual.

 

Yes I thought of this overnight and thinking of just getting S5 harness. Will pull motor out and see what's salvageable. Previous owner said it had a streetport.

So I guess I will just sell the S4 engine, too bad because its really a complete motor!

 

S5 are a lot harder to find than s4 as well as more expensive(because they're more rare), you should be able to find one around the same price which usually is $400-700 if its running, make SURE the engine you have has been compression tested first. You'll want it to have 90+ psi at least on each face minimum.

 

Right, but before I buy a motor I want to see if the existing block is still useable.

If not, I will just wait and get me t2 motor instead. Not really in a rush, so patience will pay off

 

What's the reason it stopped running?

 

It was in an engine fire. Wire harness melted along with hoses and plastic parts.

 

swap the front cover, make a special blockoff plate for the EGR to clear the S5 UIM and basically run everything from the series 5 engine on the S4 keg.

almost all the differences between the engines are internal.

 

Subscribed! Id like to find out what you end up doing with this situation. GL!

 

I'd rather not take the complete engine apart and piece it with an S5.

At first I was thinking of rewiring it to an S4 but it will be too much. I will just source S5 parts that need to be replaced, besides the harness.

 

just the front cover has to come off, the engine doesn't need to be disassembled further than that.

working on a series 5 vert with a s4 keg in it at the moment, which incidentally had a bad s4 engine swapped in so just redoing it all the way it was. yes, an s5 keg swap would be best but not always what you're going to find or end up working with.

he could have found a used s5 motor, paid to ship it, rolled the dice and wound up right at square one. sometimes you need to take the economical route that will work even if you take a slight hit to the performance. sometimes this involves working with just what you have and see what the outcome is.

 

If it was only wires and other stuff it should be easy to fix , if it still turns over you can compression test it to be sure its worth putting your time into.

 

looking at that bay i am willing to bet the engine isn't worth even trying to turn over. it may be rebuildable but even that is questionable. the top of the engine likely saw temps as high as 400F, which will compromise most of the seals inside the engine.

 

That's a good point.

Also, apparentely in order to transfer a title in AZ now, you have to have registration. So originally I wasn't planning on passing emissions, so now I have to take that into consideration.

Hopefully motor comes out this weekend and I can really see what I'll be doing