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So let’s start off with the obligatory statement, this is what worked for me. Proceed with this swap at your own risk; physical and financial!
So you’ve found the perfect FC for sale on marketplace. Pictures look good, little to no rust, most of the interior is there, the price is decent (for today’s prices); but it’s the same as most of the FCs for sale….rolling shell only/no engine or trans. So you do the thing we’ve all done, go on Ebay and see how much a motor and trans is going to cost you. IF you can find one, you realize you’re going to spend more on a used 150K mile engine than you will for the shell. So you sink back in disappointment and start dreaming of cramming an LS into it because at least then you can still drive an FC, but you know deep down you want the doritos. Then you remember while on Ebay you saw the magnitude of Renesis engines from an RX8 for dirt cheap. Man wouldn’t it be great if you could put that in the FC chassis? So you google and find nearly nothing on anyone who’s done it. So can it be done? Do you want to tackle the arduous task of being the guinea pig to do the research of what needs to be done in order to get it in there? Well, I answered yes and I’m here to share the knowledge so that someone out there might be able to save that FC chassis on marketplace and maybe have fun doing it. The goal of this swap (for me) was to get the RX8 engine running using the stock RX8 PCM (aka the ECU) and use the 6 speed transmission as well.
Pro’s and Cons of this swap. Well the RX8 engine came in 2 forms, a 4 port and a 6 port. The majority of engines out there are 6 ports with a manual 6 speed transition. The 6 port in stock form is a nice 230HP with a decent 160ft-lb of torque. Compare that to a stock FC turbo 180HP and 180ft-lb and I think you’ll find that the cost/HP is massively in favor of the renesis motor (aka 13B-MSP). Another pro, the MSP is still a 13B at it’s core. That means it’ll bolt up to your transmission and take up roughly the same footprint as the engine that came in your shell to begin with. Parts are still readily available for the MSP engine as well. Now the cons…The MSP engine doesn’t necessarily have the best reputation for reliability. The S1 RX8s had a reputation for chewing thru engines. This was fixed with the S2 RX8s and the root cause is generally accredited to the OMP not injecting enough oil which leads to premature wear of the apex seals. In addition the oil pressure on the S1s is really low leading to bearing failure. The S2 engines have additional oil injectors which seemed to have fixed the lube issue and run significantly higher oil pressure. I personally am planning on premixing like I do with any rotary, so in conjunction with the OMP I don’t really see this as an issue. You can also swap in an FD oil pressure regulator (and shim the front cover regulator) to increase oil pressure. The other major con, is this isn’t exactly a bolt in affair, but as far as engine swaps go, there really is a minimal amount of fab work needed. This leads us into the next topic:
What do you need for this swap? A welder for sure, or at least a friend with a welder you can bribe with a 6 pack. Basic hand tools, soldering iron and wire, and some patience. Oh, and these parts too:
One of the key things to this swap is the RX8 PCM. It controls everything, including the 3 intake valves, the OMP, injectors, ignition coils….EVERYTHING. You can of course use a standalone to run it, but you’ll lose use of the OMP and the Auxiliary Port Valve. This is the valve that opens the 5th and 6th ports and gives you lots of top end power.
You’ll also need to shell out a bunch of cash for the standalone and get the car tuned. We FC owners have a reputation of being…”thrifty”…and I for one am happy to live up to that reputation. So I opted to re-use the stock PCM. This next part is very important, so read it carefully…WHEN YOU BUY YOUR PCM, BUY THE KEYLESS MODULE AND A KEY FROM THE SAME CAR. The PCM, KCM, and key are all paired together. You CAN NOT mix and match from different cars. Also make sure you are getting the correct PCM. There are 4 port and 6 port engines, manuals and autos, and the PCMs are different and are NOT interchangeable. While you’re at it, get the MAF, barometer sensor, key coil, and gas pedal if you can. So once you have your parts you’re ready to start the swap. Let’s do this in functional topics:
This is pretty straightforward. You’re going to need custom motor mounts. I’ve created a template to get you started or get them laser cut from a place like cutsendcut.com. You will need 2 stacks of washers that are about 3/8” thick that go between the mount and the 2 front most bolts on the driver’s side mount.
If you weld these up correctly, they will line up with the stock FC front cross member and center the engine fairly well. Also note that these are meant for use with the RX8 trans and will place the shifter in the correct location. If you are using the RX7 trans these motor mounts will put the engine too far back.
There should be plenty of clearance for the stock RX8 oil pan, so no need to change that out.
Using these mounts the oil filter will be very close to the firewall. It fits, but I highly recommend an oil filter relocation kit. When you put the FC heater core hoses on, you’ll have even less room
Working our way back, the transmission will need custom mounts as well. The main plates that bolt to the chassis and the trans are in the download linked above. I used the stock FC trans mount bushings.
Driver’s side:
Passenger side (before I reinforced it)
These mounts should also place the RX8 shifter right in the FC shifter opening
Further back we need to address the driveshaft. The RX8 trans happens to have the same seal diameter as an automatic RX7 driveshaft, and the automatic driveshaft also happens to have the same bolt pattern as a non-turbo FC diff. The problem being the RX8 6 speed, is about 3” longer than an RX7 trans, so 3” needs to be removed from the length. Most driveshaft shops will do this modification for you and balance it afterward as well. Or if you’re feeling sporty, it’s not overly hard to chop 3” out. I do advise getting it balanced afterward.
If you opt to NOT use the RX8 trans, you’ll likely need a turbo FC trans as the flywheel on the MSP engine is quite large (larger than the FC turbo flywheel even). I can’t comment on fitment of the driveshaft either, but my guess is it will be a bit long. If you’re ambitious this has all the info you should need to mix and match trans and driveshafts
Exhaust is also pretty straightforward. I re-used the RX8 header as it’s quite unique with its 3 runners. The header does need to be modified as it will hit the FC firewall. It’s also a bit unique in that it’s made of 2 layers, a thin inner shell and a much thicker outer shell, so you will need to make a cone like piece to cover from the outer shell to the inner 2.5” pipe. I welded the first elbow to the inner shell and then welded the cone adapter to that elbow.
Firewall heat shields mostly fit. The large section at the end had to be removed as it wouldn’t fit around the new trans mounts. A little trimming was needed as well.
I connected this to a standard FC catback. My “midpipe” looked something like this
The RX8 uses a return less system, which I opted not to do. Instead I converted it to a standard return style system. You can modify the stock rails (what I did) like this:
Or you can buy aftermarket fuel rails on ebay or the like. The primary rail and secondary rail will need to be connected together at some point if you run a return style system. I opted to make a hardline to connect the two together.
If you go this route, you will need a fuel pressure regulator. From what I can tell the stock RX8 fuel pressure is round 60psi and does not rise with engine load. I put mine here, adjusted to 60psi, and just didn’t connect the rising rate vac hose.
The MSP engine will use quite a bit more fuel than the stock N/A fuel pump can deliver, so I highly suggest upgrading your pump to a walbro, or a stock FD pump (what I did).
This is an easy one. You can use the FC upper hose, and the RX8 lower hose. There is one nipple on the thermostat cover and one on the housing that can be capped, they went to the RX8 overflow tank and the heater core. There should be only 1 hose left, and that goes to the throttle body.
I went a bit overboard and made a new thermostat cover, but you don’t really too. The angle the radiator hose comes in at just won’t match up to the cover very well, but the FC upper hose will still fit.
Oil system:
Not much needed here. As I mentioned I highly recommend an oil relocation kit. You’ll need custom lines anyways, so it’s not much more work. I am reusing the stock FC oil cooler which is actually very capable in stock form with some -AN lines connecting everything.
So this is the big one, the one that took me the longest to crack. The RX8 PCM really isn’t that complicated when it comes down to it. It’s a mess of wires and it’s just a matter of figuring out what each one does. I made this spreadsheet that spells out each pin for every connector. Connectors 4 and 5 are the ones you'll be interested in.
as mentioned before you will need the keyless module, and (optionally) the OBD port. Here's the wiring schematic for those two items:
Here's the interface wiring to a S5 coupe. other models may vary.
Pretty much everything else will be new wiring. Including the ignition relay, DBW relay, and cooling fan relay (if using an Efan). New wires will also need to be run for the barometric sensor as well as the drive by wire gas pedal. And speaking of the gas pedal, you'll need to mount that as well. I modeled up a bracket adapter that you can download and 3D print/machine for yourself here: https://www.thingiverse.com/thing:5536191
I ended up machining an aluminum version, but a solid ABS print may hold up.
So those are the basic fundamentals of the swap. I'll try and address other issues, like dealing with power steering, and getting your gauges functional again in a bit. I'f you'd like a lot more detail about my swap I encourage you to look over my build thread as it has a lot of small details and a lot of other side quests that I undertook along the way.
Awhile back I considered a Renesis swap since I was having such a hard time finding an FC engine. Part of the reason I ended up not pursuing it was a lack of documentation. Things went a different way that I'm happy with, but this sort of guide is definitely going to help people in the future.
Great information, especially about the PCM integration. I am just wrapping up a JDM 4 Port/5 speed Rx8 drivetrain swap into my FC subframe swapped FB. My engine and trans mounts look very similar to yours - wish I had seen your cad files as it would have made my life easier lol. I went with a Haltech because it's what I am used to, but good to know you can use the Rx8's electronics successfully.
Again - great info!
Great information, especially about the PCM integration. I am just wrapping up a JDM 4 Port/5 speed Rx8 drivetrain swap into my FC subframe swapped FB. My engine and trans mounts look very similar to yours - wish I had seen your cad files as it would have made my life easier lol. I went with a Haltech because it's what I am used to, but good to know you can use the Rx8's electronics successfully.
Again - great info!
A standalone would be a good choice on the 4 port as you don't have to worry about controlling the APV motor. It certianly would be nice to be able to adjust the fan on temp as the RX8 PCM doesn't turn on until 207F.
thanks for the compliments everyone. Hopefully it's useful for someone!
you can just ground the radiator fan relays with a thermoswitch adjusted to a lower temp, but there’s a nifty aftermarket dual speed fan controller you can buy for $40, pull the fan power relays out of it, and run wires from the downstream vehicle fan relay ground tab into the controller relay insert tabs and then ground. It has a radiator fin insert probe and the first low speed setpoint is adjustable from 160*F up and the controller automatically turns on the second high speed setpoint to 10°F higher than where the low speed is.
essentially this just grounds the relay to turn the fan on sooner than the pcm would ground it to do the same.
or you can buy software to tune the factory pcm, but even if you adjust the temps lower in the pcm it still functions on the OE fan strategy that has a few issues. By using the controller it functions solely on temperature and bypasses the factory strategy completely. With the external controller method the pcm continues to operate as it normally would completely oblivious to no longer being in control.
or you could just wire the whole fan system through the same external controller, but that entails all the power wiring etc. rather than two small gauge ground wires. Or one wire if you only have a single speed fan setup.
you can just ground the radiator fan relays with a thermoswitch adjusted to a lower temp, but there’s a nifty aftermarket dual speed fan controller you can buy for $40, pull the fan power relays out of it, and run wires from the downstream vehicle fan relay ground tab into the controller relay insert tabs and then ground. It has a radiator fin insert probe and the first low speed setpoint is adjustable from 160*F up and the controller automatically turns on the second high speed setpoint to 10°F higher than where the low speed is.
essentially this just grounds the relay to turn the fan on sooner than the pcm would ground it to do the same.
or you can buy software to tune the factory pcm, but even if you adjust the temps lower in the pcm it still functions on the OE fan strategy that has a few issues. By using the controller it functions solely on temperature and bypasses the factory strategy completely. With the external controller method the pcm continues to operate as it normally would completely oblivious to no longer being in control.
or you could just wire the whole fan system through the same external controller, but that entails all the power wiring etc. rather than two small gauge ground wires. Or one wire if you only have a single speed fan setup.
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yeah, the fan I have came with a standalone controller, but it's pretty clunky. Might be an option going forward, but I do like the idea of the thermoswitch as well.
Figured I should add a bit more clarity to the PCM control and how the keyless system need to interact with they system. The PCM, keyless module, and key are all coded together, but you need another piece to make it all work. you need a "coil" as mazda calls it. It's the T1-01 connector referenced in the wireing schematics above. This is the part that reads the chip in the physical key and is in the steering column. This part is common to the RX8 and the mazda6, so you can steal it from either vehicle. This is what it looks like:
I 3d printed an adpter which you can download here, cut down the key and you're good to go once wired in as shown in the schematics.
So wanted to address a few more things that are semi-important for this swap. The first being power steering. The RX8 uses an electric steering rack so there is no bolt on power steering pump. Lucky for us lots of OEM manufacturers have gone to electric powered power steering pumps. A very popular unit is the volvo, and can be sourced in a few of there models like the C30, C70, and S40. I found a V50 at my local junk yard that had the pump and wiring still. Here's the unit with the mounting bracket from right out of the V50
I ended up hacking up the original mount just for the mounting studs and made my own brackets:
Here's where I mounted it. It required pretty much no modification except adding a few rivnuts to bolt too
from the underside
Of course mounting it is the easy part. the pump is controlled via a CAN bus signal on the volvo. Lucky for us this is such a popular pump that companies sell aftermarket control units for them. I'm currently using this one with good success. I'm just using the one with the potentiometer control and short of the pump running when the car is in the accessory position, it works like a champ even at the lowest setting.
The next thing is fittings. There are a few variants of the pump so you'll need to look around to see what fitting you need. The pump I got had a M16 port for the pressure side.
and have not had any leaking issues to date. I won't go into detail on what fittings go where as there are plenty of threads on this forum that cover that topic.
The other big topic i'd like to address is the speedometer. The FC uses a cable driven speedometer taken right from the FC trans. If you're using a FC trans, this isn't an issue, but if you're opting to use the RX8 6 speed you got problems as the RX8 trans does not use, or even have provisions for, a cable drive. This is another one of those problems you can throw money at to make disappear. Speedhut makes a GPS cable drive unit that works really well, but I believe there are a few others on the market as well. If you're going to order one, order the "ford style clip on" cable as well. as it's nearly a bolt on cable that requires only trimming the guard on it back a bit. For reference Ford cable on top, stock FC cable on bottom
Once trimmed it plugs right in. The only caveat being that the plastic retaining clip doesn't actually work. Not a problem, all you have to do is deform the guard a tiny bit so you have to force it over the cable post on the gauge and it'll stay right in place.
Here's where is "mounted" mine. I need to go back and do something better, but it fits right in this cubby in the HVAC units on the passenger's side very nicely. It's also where I have my OBD2 port "mounted".
I can confirm that the Speethut GPS speedo drive with Ford style end trimmed down works on a FB too in case anyone cares
Good info on the Volvo pump since the MR2 pump, which used to be the go to solution has become difficult to source nowadays.
I'm currently running a manual rack on my car, but want to go with power eventually. I had been debating going with the powered column route that seems popular with the K swap miata guys (among numerous others), but the electric driven hydraulic pump like you did seems much simpler.
I think there's another electric power steering unit out of a 2005-2009 mazda3 that's gaining popularity as well and can be found fairly readily. Not sure if there's any aftermarket control support for it yet.
Yeah, maybe I'm just getting to that age, but I greatly prefer having power assist steering. The FD I just got has a manual rack in it and it's on the list of things to get replaced.
I am looking into doing this swap myself. Seem to have most of my bases covered but I'm trying to figure out the dbw setup. Connecting the pedal seems fairly straight forward, just connect where they normally go on the pcm, and I wouldn't be hacking up the engine-side of the harness so throttle is ok, but I am seeing 2 pins for dbw relay.
looking at the relay, it seems it is actuated by pin 5H and the EGI INJ 15A fuse and just bridges the ETV 15A fuse to 4C. I don't think I'm fully understanding the purpose of this unless the purpose is to "turn off" if the fuse for the fuel injector pops. Is there another purpose I'm not seeing or understanding or is this something I can just wire 12v to 4C in a pinch? Reading wiring diagrams like these isn't exactly my strongest suit so I wouldn't be surprised if there is something I am missing. Love all the information by the way, it is extremely helpful
Hello. thanks for the kind words. I'm glad it's helping people out.
I'm not 100% sure why the 12V supply for 4H is taken before the main relay. The ETV(electronic throttle valve??) fuse also supplies power to switch on the main relay so I don't think it's a safety feature, and the main relay supplies power to a lot of fuses so I can't imagine that it's a current limitation of the main relay. My only guess is that they wanted a very steady 12V on pin 4H so it was taken before the relay?? Maybe someone smarter than me has better theories....
What I can say is that I would not put 12V right on pin 4H. There may be some logic in the ECU that looks for voltage at 4C while looking at the state of pin 5H. What I DO think you can do is use the same 12V source for the ETV relay 12V inputs (W/L and Y/G wires on B1-02 connector).
Since I am running my Rene with a Haltech I didn't spend much (really any) time on the factory wiring diagrams - but I took a look and as you guys said, 5H will draw/sink to ground to activate the DBW relay - which in turn will send 12v through to pin 4C on the PCM.
I am guessing during normal operation with no faults this relay will always be on supplying 12v to the PCM - which I assume is the voltage actually going out on a pair of half bridge's to actually run the throttle body. During a fault of some kind the PCM would be able to immediately cut power to the DBW to keep the engine from "running away" (since the throttle body still has a return spring in there it will close once power is taken away).
Again, only a guess as I gave very little time to figuring out how the RX8's electronics work since almost all of it went in the bin on my setup - although I am still using the stock throttle body - the Haltech makes it incredibly easy to setup as all of the drivers, including a redundant setup is all internal.
Also, from the looks of it, the ETV 15amp fuse is not switched - it is constantly hot.
09-27-22 | 10:11 PM
Oil system:
Oil system:
