FC/FD intake on 12A question
 

Anyone running an FC or FD (or any combination of UIM/LIM) on a 12A to go EFI? Thinking about going this route cuz it would be cheaper than going throttle body injection and more efficient (theoretically). What's your set up?

How are you going to inject the fuel? 12A housings don't have the injector ports in them. Its a lot more complicated than just getting the intake from and FC or FD. You will need a standalone or an ECU of some type as well.

It would be easier to swap in an FC engine/ECU than try to convert your 12A to be EFI.

What he said. You don't need the manifolds for EFI, you'd need a center housing from a GSL-SE for the injector bungs. Or a throttle body setup on a Holley or Weber type intake manifold. Which, admittedly, is light years better than the OE Mazda intake manifolds anyway.

I’ve done it two different ways
first time I used an adapter plate I made and put injectors on t2 lower intake,second set up It was a bit more complicated and cut down the turbo lower intake down to size so it bolts up directly to the 12a engine.

Here is another I did for a friend

Very nice work...

So I have this Atkins sidedraft manifold, I am thinking that putting injector bungs on it and using a dead DCOE carb would be pretty sweet.

The side mount manifold are long accepted to be the best for power output especially on engines with tall center ports.

It's kinda funny. I'm trying to go the opposite way. Putting a 12A carb on an FC or FD engine.

I mention this in case you change your mind.

Generally I think thats true but remember the header is right below it. You will need to heat shield it good to make it reliable.

Why? There's enough airflow through the engine bay that it doesn't matter.

I've done it both ways I've bought a plate made it to mate the 12A to the T2 intake and machined that for injectors and I've also gone with the 5 letter center iron with the plate to retain a factory like Injector position . I was trying to find a way to use the S5 computer but instead a friend wired one in.
I was searching for a while on here for something like that and it was actually Turbo Dave i think i saw do it and than i found a company in Australia online that sells them.

Here's the thread I found:

https://www.rx7club.com/old-school-other-rotary-63/rx2-sedan-12a-turbo-project-928917/

This is exactly what I was looking for, how significant is the power and throttle response increase? I mainly want to do it for reliability and improved gas mileage.

Thanks!

Gas mileage?... It's all about those smiles per gallon, not miles per gallon :biggrin:

You know you'll need an aftermarket stand-alone fuel management system as well with this as well, correct? Something that will tell the injectors when to fire, the timing, all of that would come after the installation. I'm thinking at least $2,000 in an upgrade just to get a few more MPG's isn't worth it.

As of right now I'm getting 14 MPG combined, combined with constant spark fouling and occasional flooding, not mentioning stuttering if I try to accelerate quickly. It's all those reasons why I want to upgrade to EFI over the holley. I'm not planning on buying anything new either so the price would be closer to $800 vs $2,000.

Recently my buddy informed me that if I upgrade to electronic ignition and play with my timing I could eliminate the problems I've been having with the holley; I might go that route because it would be a lot cheaper for the time being, though I eventually want to move to EFI.

Upgrading to direct fire is one of the best things you can do.

Finding a used ECU to run the system as well as the parts alone will cost you more than $800. I have an REW upper intake, lower intake and throttle body setup for sale right now for $220 shipped and that's most likely the cheapest you'll find the parts. Then you're talking fuel pump, fuel lines, custom fuel rails, fuel rail fittings, hose, wiring, wiring connectors, injectors, custom work done, it's going to add up to more than $800 no matter how you do it.

Follow Jeff20B's advice and go direct fire using his method, it's foolproof and very well documented as being effective.

I'm going this route for next year, using your method on the 13b PP I'm building. Will respond to your PM here in just a minute as well, sorry I keep forgetting to!

If you already have the manifold, why not use an EFI specific throttle body that’s already set up for injectors and a fuel rail?

I was thinking about something like this on a wrap-around side draft style manifold.

https://foxinjection.com/collections...dy-45mm-single

Depends on your point of view. In my opinion anything you can do to minimize petroleum use is a Good Thing, for various geopolitical reasons.

Also, I have yet to get better economy with injection than a carburetor on a rotary. Better drivability with wild ports, but if I were looking for max economy I'd build a stockport 12A and run a stock Nikki with some ignition timing tweaks. But to be honest it is way cheaper to put fuel injection on a 13B, including the 13B, than to build a 12A engine.

Oooooh, geopolitical reasoning eh?! We should all switch to Geo Metro's or Prius's then, or even better yet - Tesla's! :lol: [See response in next quote]

I built the RX-8 6 port Renesis with a 6 speed manual transmission and every reliability modification possible. Still only gets 17.61mpg on average, with proof:
https://cimg1.ibsrv.net/gimg/www.rx7...36a0730a05.jpg

I got better gas mileage with an unmodified 12a with the Nikki carb that was literally 20 years older than this RX-8!

So switching to EFI on a rotary doesn't get you any better MPG in most cases in my opinion. I'd love to have someone combat this theory with me, as I have many more gas mileage records for this RX-8 and some of my RX-7's. I'm talking semi-stock, not heavily modified cars. That defeats the comparison.

I've seen 32mpg with a 12A (running 4.78 gears and cruising at 5000rpm!), although I could normally expect 27. The thread about that run was epic. (Cliffs notes: Yes, I was accounting for odometer error. Uncorrected MPG was over 40)

I generally do about 20mpg with my bridge ported 13B, which sucks since I used to get about 24mpg, but the engine is extremely tired, and anymore when I do long distance drives I am towing a maybe 700-800lb trailer that is almost as tall as the car. So in reality that isn't too bad. I'm thinking of putting in a 2.5l Duratec, which should be able to make about the same amount of power with a proper header, but with much better fuel economy and FAR cleaner emissions. I'd love to put a cat on the car again, which simply will never happen with any kind of high powered rotary.

This is mostly why for the past couple years the RX-7 sits and drips, while I have been driving a turbo Volvo that emits unicorn farts and rainbows from the tailpipe and gets up to 40mpg (actual).

True story, when I first got my fat nikki installed and running I was seeing 30MPG on the highway. Its was way lean, this was with the stock jets. Now it gets 24MPG and is way more fun to drive as well. I can probably go richer but I want to get a wideband and tune it proper like next time I'm messing with it.

Before you throw the Renesis motor under the bus, keep in mind that the RX8 weighs 3,100 lbs compared to our 2,000-2,400 lb 1st gens and it also makes double the power. Get a 12a to make 220hp then drop 1,000 lbs in the hatch and see what you get for mileage then.

That's incredible! I've been contemplating running the Kia diff in the back of my FB next season with the peripheral port motor I'm building but haven't committed yet. Do you still have it or would you recommend it? That's just insane mileage with that rear end in a car in my opinion.

Exactly, just proving my point. Even a bridgeported carb'ed rotary still gets better mileage than a Renesis does with a few decades of technology furtherance.

I'll be the first one in line to chuck that Renesis motor under a bus. The RX-8 with an REW would have been another cult classic car from Mazda (if it could have passed emissions and gas mileage standards, that is). As cool-ish as the 8's are, they don't hold a candle to 7's in my opinion.

The RX-8 is definitely a pig in the weight category though, luckily it makes up for it with the handling. The suspension on the car is unbelievably well-done in my opinion for a stock car. Thing just hugs the corners at any speed the tires can grip. Absolute riot to take around a corner quickly in my opinion.

I would not recommend it for several reasons. For starters, you could always just drive in 4th gear. 5th with an FB trans and 4.78s is like 4th with 3.91s. Plus you'd have less drivetrain losses since you'd be driving in a straight-through gear. (The ND MX-5's transmission doesn't have an overdrive for this reason)

With a high overlap engine you want TALL gears so you can load the engine under cruise. I'm talking run the stock 3.91 and then use the year FC transmission that had a .697 overdrive. High overlap engines hate to spin unloaded.

And my engine isn't carbureted. I've been on the Megasquirt train since 2008-2009 or so. The drivability you can get when fueling isn't tied to depression through a venturi is incredible. I can idle at 700rpm if I want to. But the fuel atomization isn't nearly so good, so economy sucks since you end up having to run richer than ideal in order to be able to ensure that there's an ignitable mix near the spark plugs.

You could PROBABLY tweak a carb to work just as well, but you will have far more money and especially time invested in jets and air bleeds and emulsion tubes and screwing around making it work, than you would have just plugging your laptop into HAL and telling it what to do and when to do it.

Just as an example of the kind of things I am talking about. With my gears and tires, I cruise on the highway at 3500-4000rpm. On flat ground, the engine is running at maybe 50kpa and I need to richen it up to about 12.5:1 or so at the high-vacuum end of cruise in order to keep it from bucking and misfiring because of all of the exhaust gases dirtying up the chamber. When going uphill, especially with a trailer, manifold pressure goes to 80-85kpa and the engine will sing sweetly at 15-15.5:1. Injector duty cycle actually stays the same at the higher load, because it's getting less exhaust gases sucked back in so less fuel is needed to be dumped in to ensure stable combustion.

When I had a stockport GSL-SE engine, I could barely get 20mpg.