bart_heemskerk

Hello, i am Bart and i have a question. I am stuggling with the nikki carb so i bought a mikuni carb and a sidedraft manifold. Then i found that the carb is mounted at an angle compared to the engine. In a rx-7 the engine is a bit tilted backwards, but i have it mounted level. So the carb is not level. To make the mikuni work it has to be level, so i have to modifie the manifold. That means cutting the manifold and fabricate a angled fillerpiece and weld that in. And then i can start tuning the mikuni.

As i have megasquirt allready present in my car (from the previous engine) i might be easyer to convert to EFI, instead of cutting the manifold tuning the mikuni.

I thought of using the mikuni as throttlebodys (without the venturi ofcourse) and drill two injectors in the manifold like this:





Will this work? What size injectors do i need when using two injectors? It is a 1983 12A stock port open exhaust.

T2GTUS

Seems like a bit of work, but I imagine it would work ok ... I would think you would need at least 2 680cc or better injectors(its a similar setup to a gsl-se).

rmriggin

I know that setup will work because I have seen it work. If you got access to a good tig welder and someone that can use it you can get some injector bungs and fab something up.
The size suggested seems right on spot for running a 12a without boost. Since technically you will be running throttle body injection tuning it could be a bit of a hassle.
I believe pmrobert is running a similar type setup on his megasquirted 12a. Might want to get some pointers from him if possible.

bart_heemskerk

Thanks
The gsl-se injectors: are these low or high impedence?

Jobro

iTrader: (2)

I'm guessing low because Early TII's are low, and then late ones switched to high, and generally they changed over to High Z injectors as things got newer.

You can of course measure with a Digital Multimeter.

Low Z ~2-3 Ohms
High Z ~10-15 Ohms

You can also just use 10Ohm 10Watt resistors to make the Low Z injectors look like High Z injectors to the ECU anyway, this is what I plan on doing!

renns

I ran an old-school 13B with high-mounted injectors, and it was great at the top end. Idle on the other hand was terrible. After 10 seconds or so of idling, it would slowly load up and stall. Squirting against the runner wall so far from the port likely resulted in poor atomization at idle. At least that's my guess, given Mazda put their primaries as close as possible to the port. Your proposed location is quite a bit closer, and may not be as much of an issue.

bart_heemskerk

Made a start with it.

Bought 2 of these bosses and welded them in the manifold.


Made an "intake box" from aluminium.


The throttlebody has two butterflies. A small one for low revs and a big one.


Made a fuelrail from some copper pipe and some brass fittings.


On the side of the box i put the fuel pressure regulator. On the back is the fast-idle solenoid.


And bought a fuelpump and 720cc injectors.


progress is slowly but i am satisfied so far.

SCCA RX7 RACER

I feel you may run in to the same problem as Renn. Two racing buddies of mine removed the defusers from below there injectors and had the same top end but no mid range and screwed bottom end. Their thought was to have better air flow. As it turned out the fuel was hitting the walls and not mixing with the air. If you want to inject you have to move them closer to the intake ports and have the spray from the injector dispursed. Or if you run PP then you can spray direct in line of the intake runner to the port back by 6 to8 inches. Remember PP is for top end mainly thats why it works. Best Regards SCCA RX7 RACER.

bart_heemskerk

Got everthing build in and wired up. The engine starts inmediately! So far so good.... not. It idles very rough. i have to get the mixture very rich to keep the engine from stalling. The wide band lambda is jumping rich to very rich when the engine is idling rough.

The squirt is set to 2 every cycle. If i put it to 4 or 1, the engine dies straight away.
I have two 660cc injectors and the PW at idle is 1.8-2 ms.

When i open the trottle a little, the lmbda is jumping up en down from very lean to very rich.

Is this because of what "SCCA RX7 RACER" said? (As it turned out the fuel was hitting the walls and not mixing with the air)

Oh, an other thing: i am cranking at 700 rpm. Is that normal for a rotary?

toplessFC3Sman

iTrader: (1)

It will be a bit rough and slow to respond at idle since you have such a small amount of airflow. The fuel will be spraying into almost stagnant air since both ports are open and flowing at a much smaller velocity than if just one port was open (as in the stock -at least for FC's- configuration), so the fuel doesnt get swept along by the air as well and mixed. Plus, the intake velocity is much slower so less air can get packed in the housing due to charge momentum, and some of it is probably pushed back out into the intake manifold even with stock porting. To get enough fuel to initially vaporize so that it will ignite, you therefore have to spray a lot more in. When you're closer to stoich, all of the fuel does eventually burn, causing the rich reading on the O2 sensor, but not all of it is vaporized to burn steadily/reliably at the time of the spark, causing the rough idle.

300 or so is normal for cranking speeds... 700 is pretty insane.

bart_heemskerk

I put the efi stuff in a corner and i'm back on the road again with the good old nikki.

What i don't understand is why this setup is not working. If a dcoe throttle body with injectors is working, mine should working aswell? It seems to me that on a dcoe style throttle body there is the same amount of airflow???

On a 13b gls with two injectors, whwre are these injectors situated?

pmrobert

I have a 12A injecting that same manifold with no concerns. My injectors are located in Weber Alpha TBs and I use MegaSquirt. There's an image attached, please ignore the all-rubber fuel lines, this was the proof-of-concept before I fabbed up the hard lines. The thing was a bit of trouble to initially tune, especially in the AE department. That install is actually the genesis of MAPdot AE, initially due to the fact I couldn't easily fit a TPS in there. I still don't have one and the build is currently being redone with a T3/T4 turbo to assist things. Please can the Nikki and let's see some datalogs.

-Mike