My S5 NA engine is dying.
Can't really complain, at 250k miles low compression and high oil consumption are to be expected and she still runs surprisingly well (no hot/cold start issues, no excessive smoking, etc.) but I'm planning a long road trip (3k miles) in late August and for the first time I'm worried about making it.

I've long desired a V-8 swap but right now the money just ain't there, even a basic rebuild of the rotary is beyond contemplation (I am the prototypical broke *** FC owner).

Recently, the possibility of obtaining a S4 NA motor arose which would at least buy me some more time on the road.
Compression and oil pressure are supposed to be good (and I have no reason to doubt the seller but haven't confirmed anything yet).

So, here's the question...
Can I transplant my recently refurbed S5 engine peripherals (primarily intake and clutch/flywheel) onto the S4 shortblock?

I'm aware of the basic differences between the two motors (different balance weight on the flywheel, different OMP setup, etc.) but don't know if there's anything fundamental standing in the way of transferring my parts to this new(ish) engine.
It would be considerably easier if I could just swap in all my S5 engine management/sensors, etc. rather than convert to S4 ECU/harness/parts.

Any info appreciated.

 

You'll have to swap the front cover also to keep the S5 OMP. Not sure if the front iron on the S4 is compatible though.

 

^^^ That, and your ECU will need the S5 OMP.

 

true issues: MOP and maybe the knock sensor(s). everything else should physically/functionally transfer over to the S4 block with perhaps a block-off plate or two thrown in there.

 

Clokker shouldn't have issues with knock sensors since he has an NA S5. He will have to block off the EGR, I forgot about that one.

 

Yes, JJ, I'm thinking he'll want to keep the S5 ECU and OMP (and so will need to put the s5 cover on the s4 engine).

 

This is one concern I had, although the gaskets look identical save for the oil passage o-ring area.
I'd certainly prefer to just swap the front cover and retain the S5 OMP but can block off/premix (keeping the OMP connected but tied off somewhere) if necessary.

The S5 LIM will work though, right?
And can I just swap the rear counterweight to the S5 flywheel?
Blocking off the EGR is no biggie and the knock sensors can just be discarded, I assume?

Thanks for the info so far.

 

Lim and front cover will bolt up just fine.

Are you using an aftermarket flywheel or stock?

 

S4 LIM needs to be used in order to keep the "port air" emissions system functional. You are pretty much doing the S5 intake on S4 modification. I followed the guide here, but the pictures are gone.
89 Intake Swap Introduction

The biggest hassle is grinding away the passenger side mount for the 'clutch inspection cover'. It's kinda messy, but it needs to be done.
The EGR must be discarded, but it doesn't help with emissions anyway.

I can confirm all the S5 rats nest, etc bolts straight up to the S4 block. Little stuff like supplying vac to the OMP nozzles, BAC valve, routing coolant to the TB, etc. requires a little ingenuity and a hose parts bin. So basically right in your wheelhouse.

 

Stock flywheel, recently resurfaced w/ new clutch.
OK, this is confusing...especially since the pics are gone.

 

If you have an aftermarket flywheel then you need the Counterweight for that Specific engine that you are attaching it TO.
So if your old engine was S5 with an Aftermarket flywheel,you now need an S4 Counterweight to go on the S4 Engine.
The aftermarket Flywheels are "universal".What makes it different(from s4 to s5,etc) is the Counterweight that you attach to it.

 

this will be a slight snafu if the S4 doesn't come with a flywheel. I see them for sale in part-outs all the time, but of course, when you need one then they become like that palmetto unicorn. you will need one. your present clutch should be good to go when you get the flywheel.

 

Rear counter weights are not replaceable on stock flywheels. You might be better off just using an aftermarket flywheel. Port air emissions aren't necessary unless you're in an emissions testing state.

 

I had to be typing and correcting when Clokker answered..heh!(my keyboard and eyes keeping fighting!)

 

OK, now I'm confused.
Looking at Mazdatrix, it certainly appears the rear counterweight is a bolt on part...is this only for "light" flywheels and the stocker is all one piece?

It's academic really, the engine comes with tranny/clutch attached, I was just trying to save the resurfacing cost since I just had it done to the S5 flywheel.

 

You're gonna need the counterweights and or flywheel that came with the original engine. You are really matching the counterweights to the rotors. The S4 rotors are heavier than the S5, so you need that entire S4 block, from front counterweight to the flywheel.

-J

 

OK then, that's handled...I'd get the stock flywheel with the S4 engine.

So now it's the LIM I wonder about.
The S5 manifold will bolt on but the port air injection will be non-functional?
Colorado does have emission testing but I'm good till 2015.

 

yes. the S4 NA only has the port air injection going through the end irons, and everything else 81-2003 has it going through the rectangular port under the primary intake ports.

the S4 has the EGR passage there instead.

if you decide you don't care right now, its fine, everything else fits like it should

 

why mazda decided to put EGR on a wankel engine just blows my ******* mind.

The large combustion area, along with the longer combustion stroke with 2 plugs just blows my mind. It isn't NOx that they needed to worry about, but the unburned HC coming out the tailpipe.

If I could, I'd add a 3rd plug like the 787, but like most rx7 owners, I am broke. :p

 

Turns out I did take a picture of the S4 casting that needs to be ground off.
Second pic is of a later engine without that casting. Yes, it was outside for a while.

The third pic is a casting on the housing. During test fitting, it was very close to touching the manifold. The guide didn't say to do it, but I took it down about 1/8" and it fits.

Once you get that casting and the EGR taken care of, you can just put all your S5 stuff on. Then it's just the OMP and routing the vacuum lines for emissions (if necessary).

 

Ah, thanks, that was helpful.

 

Clokker, from you I demand a 6 rotor frankensteined from junkyard Sevens, Subarus and Toyotas.

BEGIN!!

 

Well, I was thinking of strapping a Harley V-twin sideways to the front with the crankshaft coupled to the e-shaft.
Use it as a starter motor.

A few minor technical issues to iron out.

 

The separate counter weight needed for light flywheel are off auto engines. Just as a bit of info. Sounds like it'll come with a stock flywheel anyway

Sent from my GT-I9100 using RX7Club

 

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