Yo! Are YOU still messing with carbs and have trouble to get them to run right? EFI conversions are complicated and expensive? Or maybe your car is already EFI but standalone ECUs are expensive?
No longer!!


(middle-click on the pictures for a higher resolution)

So I converted my 12A half-bridgeport RX-7 to EFI + ITBs for cheap using Speeduino and some used parts I had laying around. I wanted to share my experience for anyone interested. Might make a video about it at some point.

450€ Speeduino PnP ECU including onboard wideband-controller, o2 sensor, air temp sensor (all of this can be a LOT cheaper if you put the parts together yourself)
80€ used throttle bodies and TPS of a Suzuki GSXR750
20€ trumpets
40€ used NA miata engine wiring harness, fuse box, water temp sensor, fuel pressure regulator
60€ used RX8 yellow injectors (4x425cc)
20€ used RX8 trigger wheel
10€ used NB miata hall sensor
40€ high pressure fuel pump, filter, hoses
15€ vacuum collector
50€ various bits, aluminium material, silicone hose, clamps etc
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TOTAL: 785€

Keep in mind you could even go a LOT cheaper if you wanted by buying or building the individual Speeduino components, or by using the stock manifold/throttles. In essence the core ECU is an Arduino Mega for 15$. Personally I wanted to save myself some hassle and also put ITBs on.
So far this is a fuel-only setup, controlling the ignition can easily be done also, I will get it done at a later date. Most people go for IGN1A smart coils but I want to find a way to do it for cheap while still having strong spark and easy accessibility of parts here in Germany/Europe.

About the car: so far its basically a stock 1st gen. On top of that I half-bridgeported the engine, also for cheap using a gasket kit from RockAuto (~130$) and new Atkins apex seals&springs. The other seals were somewhat in spec. The gearbox is from a miata, modified to fit (it has better ratios). The header is a 13b Racing beat header that I cut&welded to fit the 12a.




FUEL PUMP:
First I changed all the fuel hoses to a higher pressure variant. Then I installed the replaced the fuel pump with a new inline high-pressure generic OEM-tier pump, suited for an 80s 6-series BMW, you can get it for cheap at any regular parts store. I also made a nice aluminium cover. The filter is meant for an MX-5. The pictured 180° bend in the hose caused trouble later and got replaced with a hardline afterwards



MANIFOLD AND ITBs
Then I built the manifold to adapt the Suzuki GSX-R 750 throttle bodies to the 12a. aluminium plate and tubes, some tig welding and the job is done. of course the insides were smoothed and polished afterwards.
The vacuum collector is mounted on the manifold. It connects to the throttles, fuel pressure regulator and brake cylinder.
The GSXR fuel rail parts were bored up as much as the material allowed, and welded a flange to it for the fuel pressure regulator off of a miata. I then had to lift the rail a bit with spacers so the RX-8 injectors would fit, and use some generic O-rings to seal the injector to the throttle unit.



Unlike the stock carb, these are not staged, I will look into staging the secondaries at a later date for better fuel economy.

WIRING
Next I took a miata engine harness and fuse box for convenience and stripped all unneeded wires out of it. The plug on the TPS was swapped to fit the harness. The water temp sensor is in the water pump were once the choke switch sensor was. the air temp sensor is tied to the intake. the 12V source is connected straight to the alternator.

CRANK SENSOR:
If you want to a fuel-only setup for really cheap you could go with just a tach signal from the coils by using e.g. this converter board. I actually tried it and it worked, but want to control ignition at a later date which requires more accurate timing. The easiest way for this would be to go with a stock FC CAS. However I wanted to do it cheaper and have better part availability, so I used an RX-8 trigger wheel and a NB miata hall sensor mounted to a little tab, and drilled new holes in the trigger wheel to align TDC with the sensor.



TUNING:
Configuring the ECU tune using TunerStudio was simple. TPS-based control algorithm (Alpha-N), "4 cylinders", 2 squirts per cycle, simultaneous injection (for now, need to rewire injectors). AutoTune made building the VE table easy. The bridgeport wanted some more fuel at idle to run right. Accel enrichment is good so far but needs some more fine-tuning. In my setup ignition is not controlled yet but the options are there.

CONCLUSION:
The car runs and sound great! Of course due to the bridgeport it bogs during low rpm cruising. Starts up immediately every time. I've been daily-ing it now for weeks without issues.
It honestly was not hard to do and didn't take long. EFI now opens the door to further wild modifications.
Here's a little clip of it idling. As for the power, its good, but I feel like the small stock exhaust is likely a big bottleneck - I will fab a 2.5" system up soon. So more to come in the future...

If anything is unclear or I can help with anything, let me know and I will do my best. Let's EFI the world and keep rotaries alive ❤

 

I imagine the car runs kinda stock with the exhaust. Do you have an idea how similar to megasquirt it is? Seeing that it can be tuned in tuner studio I am interested in trying it on one of my 1stgens.

 

By now I have built a custom 2.5" exhaust which was the last bottleneck and really unlocked the engines power. It pulls!

In essence as of right now a speeduino can do everything that a ms2 can do, and more! Since its open source and an ongoing active project, features are being added frequently. But it already is way past the point of what I personally could make use of.

 

Hey Kraid, I've been working on running a renesis with speeduino. I'm using the stock injectors for now and a mechanical throttle body. I was just curious about what your startup and idle settings look like in tunerstudio, I'm also trying to deal with the variable intake system. I'm trying to scour the web for some info on any of this and coming up pretty empty.

 

Hey dude, good luck on your project!
Speeduino supports the crank timing wheel pattern of the RX8, the RX8 ignition pattern/outputs, as well as staged injection. I use all of these on my engine with great success. So no worries there!
As for startup settings that I use for my setup, they are most likely not very transferable - but it doesn't really matter much. startup settings such as priming pulsewidth essentially just affect how quickly the engine turns on, so don't worry about it and leave them how they are and go from there. As you probably know rotaries are prone to flooding so It's important to not go overboard.
For idle settings, they are very specific to the type of idle control valve solenoid. Maybe start with opening your base throttle position first, and then work on idle control later. I personally don't even use any idle control on my ITB setup; so it idles a bit higher when warm but thats ok. By the way, people have also had very great success with using the "idle advance" function that uses ignition timing to control idle instead, in case you don't want to bother dealing with solenoids / setting up PID etc.
I'm not too sure about what type of devices the RX8's complex intake system uses. To get the most out of your intake you should eventually try and make it work though. It should be possible - either by using spare outputs, or if the intake uses solenoids you could technically use the VVT outputs. But again, maybe start with getting the engine to run first and go from there. I remember a mazda workshop manual actually describing at what RPM range which constellation the intake is arranged at, so that should be your target.
BTW when you wire everything up make sure to verify your wiring is correct and read through the Speeduino wiki carefully.
If you have any more questions you can also join the Speeduino Discord. You can find me as well as some others with rotary setups there too if you need any help.

 

Now that I'm having a look at this older thread again, it's worth mentioning that even though the dizzy worked fine, I eventually started controlling ignition with IGN-1A coils and added an oil pressure/temp sensor for some safety mechanisms.
Not pretty, needs some more work. But has been running great as my daily for years without issue.

 

Oh yeah, and here is some Nürburgring footage from years ago. Admittedly when accel anrichment wasnt set up correctly yet, all been long done by now

 

Have you had any issues with fuel starvation below half tank?

EFI converted FBs usually have a surge tank or modify the stock pick up to counteract fuel sloshing away when cornering.

 

Yes, true, I do! Below half tank and there is starvation in heavy cornering, so on the racetrack I refuel when it is about halfway. I was looking into solutions for this but haven't had the time. Ideally I would like some kind of surge tank within the stock fuel cell, my gut tells me anything external is always an increased risk for leakage which I'd like to avoid.
Open for any suggestions

 

Surge tank is the way to go if you don't want to cut up the stock tank, otherwise an in-tank pump conversion like this might be available from someone in Europe.
I've never done that so I can't comment on installation.

 

Its me again, I have everything ready in the rx8 tune but im getting some very inconsistent ignition, I wanted to see if you used the same fuel calculation info. 2600cc, 14.7 stoich, 4 cyl. using 4 rx8 yellow injectors, staging enabled, therefore adding the 2 injectors together for a total of 850cc. I plan on adding the staging table later with the intake valve solution.

 

@Kraid I know this is an old post but have you refined this? Or is it still working good? I'm researching alternatives to IDA's and this looks epic!

 

@Kraid I have a speeduino in my turbo 2 rx7. I'm having a hard time getting staged injection to work and was wondering if I could possibly get your help with this.

 

I have heard good things about Hydramat from Holley. They put a trophy truck on a 45* incline with a gallon of fuel in the tank and let it idle until it died, used up almost the entire gallon. Much easier to install than an in-tank surge tank or a swirl pot in the engine bay.

 

@Kraid,
I am doing the same sort of setup right now, the issue i am having is i cannot figure out where to align the RX8 trigger wheel to TDC of the 12a. I have modeled the trigger wheel in CAD exactly so that when i find out what tooth should be TDC i can re-orient the bolt holes and laser cut the wheel. I have tried asking AI platforms and scouring the the web, your thread has the most info out there about this but i just don't understand the alignment part. can you please assist me?

Thanks!

 

So I recently got a hold of @Kraid and talked about his setup while also figuring out a setup that works aswell. so the stock rx8 trigger wheel layout.

the rx8 tdc marker is in the lower of the 2 missing teeth section. ie (the right side of image- lower one.) and is dead center of the 30 degrees {15 degrees}. I made my own bracket that comes off of the left side front cover. I have my coil bracket mounted on this location so it was just simple. hear is everything in cad.


you can see the tdc marker in this. Now where it all gets confusing. what orientation to mount the wheel. On a 12a rotate over to tdc. if you have already pulled the pulley off there is 4 ways it can go back on. yeah perfect.... but on your intake/ exhaust side there is a cover that seals the bell housing off. take it off and rotate the engine over untell the flats line up with the block.

" the cutout part lines up with the rear iron" this is now tdc r1. so look at your front hub the top bolt hole is nearly vertical. Mark this one and know that if you bring the pulley over and put it on line up the hole then your marks on the pulley up this is correct. Now back to the rx8 trigger wheel. Put it on where the tdc marker points at the pointer on the front cover. the bolt holes line up. besides 1 as mazda started to offset 1 hub hole to prevent you from messing up the orientation of the timing marks.

I have a gilmore setup on my car so i had to create a spacer that sits into the crank pulley then mount the trigger wheel. I also made a centering stub that centers off the crank hub.


my spacer has a notch to indicate tdc location. ie if its up and i put on the trigger wheel it will point at the pointer on the front cover.





now the software side. Speeduino has the 36-2-2-2 trigger option but its not native to the rx8 wheel, its for the subaru wheel. so we cant look at it as btdc r1 r2 as seen in the first pic.

take note of the cylinder 1 tdc is on the 4th tooth leading edge, and on a subaru the vr sensor it right on top vertical .

now for your off set in tuner studio. count from your sensor location to this tooth this should get you in the ball park. in my case

I started at -70 then with my timing light and timing locked at 0. moved offset untell it matched the rx8 trigger wheel tdc mark and front cover pointer lined up. You should now be right on! hope this helps others who venture down this path, and its wayyyy worth it over a fc cas!