With new injectors like the ID2000 that can allow someone to idle as well as push a hell of a lot fuel. Why run 2 rails and 4 injectors when and if one will suffice. What would the best location be for fueling. In the block position will probably help with low load and idle tuning but may affect mixtures at high load as you are injecting only in one runner. On the other hand using the secondary positions I could see causing issues with idle and low load fueling. Maybe further upstream (custom manifold) might be better as to not overly saturate one runner verses the other.

Any thoughts or practical experience with this?

 

well u need one injector per cylinder, or in our case, per rotor. i will try to explain the best i can so if any part of it is wrong, someone with more experience with FI will correct me. the injection duty cycle is all about pulse width. take a pair of 850cc injector, i doubt u can get a short enough pulse width for them to provide the small amount of fuel as say a pair of 460's will. same holds true the other way, once u max out the 850s. this is the reason u have, for a turbo engine, a pair of 850s for primary and a pair of 1600s for secondaries. even n/a might not need such large injectors as would for turbo, but the idea is still the same. and i believe this is what's known as staged injection.

 

I understand why we use 2 sets of injectors but with the new injectors you can control large injectors down into idle range. Shoot I have ran 1600cc at idle but they aren't enough for a high horsepower turbo app. The ID2000's can also be run at much higher pressure providing even greater flow.

 

If your computer allows that sort of setting, and you're using quality injectors like IDs, you could get away with just a pair of injectors. The 1st gen GSL-SE uses just a pair of 680cc injectors.

 

Again guys I completely understand I can do it, I'm a Haltech dealer and tune cars. The original question was around the most appropriate injection point; primary, secondary or upstream injection.

 

Primary position. The reason I say that is

1) the series 3 GSL-SE had two injectors, in the primary position only. this was a 6 port engine. injectors were batch fired.

2) the series 3 12A turbo (Turbo I) engine had two injectors, in the primary position only. this was a 4 port. injectors were batch fired.

3) Mazda's direct injection prototypes are using injectors in the primary port (normal primary position) for additional fuel under high loads

If you want to keep it really simple you can batch fire the injectors like the series 3 engines did. They timed the injector to the dizzy signal like other simple fuel injected engines of the era. There was no injection timing advance.

 

My thoughts as well though I had no documentation to back it up.

 

For low load and idle concerns? In the chamber! Since we can't have that, the stock primary arrangement is pretty damn good. USE THE DIFFUSER CUPS.

For high RPM/high load concerns? At the other end, with the injector pointing straight down the runner. Example:



The fuel adds to the airflow's inertia, helping VE. Pointing straight down the runner prevents any "air door" effects.

 

Like Peejay just said, there are befits to all locations. If I had to pick one for a street car, I'd choose the iron. But, if ultimate performance were desired, I think you'd still want multiple injection points.

FWIW, I did an NA setup a few years ago with a TWM setup. I used a pair of 850 injectors and did not use staged injection. Car runs great, and was easier to tune.