Hi, Novice question!
I've been trying to read a million books over the last week or two to understand how this all works. When I've read about secondary injectors (in a boinger context) it talks about having the secondaries further away from the cylinder in order to break down the fuel but also to cool the intake air. They run the primaries at lower rpm and then swap to the secondaries at high rpm. I assumed this is the same system as in a rotary? could someone confirm this ? (running a single turbo FD, was with an Apexi PFC)

 

no not the same. in a rotary the secondaries turn on in conjunction with the primaries to add more fuel. this is done so mazda didn't have to try to get 1100cc injectors to pass emissions at low rpm.

 

Are you saying that at high RPM both the primaries and secondaries are working then?

 

Not sure but I think what you're talking about is the same thing anyhow? From what I've read (again boinger arientated) the primaries are close to the combustion chamber because it helps to get full vapourisation of the fuel by spraying onto the top of the closed inlet valve (not sure how this would transfer to the rotary though?!), and thus better emissions. If you were firing secondary (and larger) injectors at low RPM further away from the chamber then the fuel would pool and you'd have poor burning and bad emissions? but at high RPM it mixes better with the air and cools it for more power.

 

Just read some other stuff and uncertain again! Do the primary and secondary injectors on the Rex swap over or do the secondaries switch on as well as the primaries?

 

Ah, somebody has just confirmed that both come on at around 3800rpm

 

I can confirm the pooling too btw! If you have staging set too low in rpm or too low in throttle position/map vacuum then you will have black fuely stains all the way from the injectors to the engine in your secondary runners.

 

yes both are on at the same time.

 

Secondary injectors are generally used when the primaries would be too big to get decently low pulsewidths to maintain idle and low load. Instead of making the car run too rich all the time, the primaries are made smaller and secondaries added.

I don't know of any system that switches off the primaries and then switches on the secondaries. To do so would create a big problem at the transition point. There would be a lean spot, followed by a massive rich spot.

Instead, the primary injectors are scaled back as the secondaries are scaled up. It's not a hard transition, it's a gradual transition that happens over a set number of ignition cycles/interrupts.

The Megasquirt provides control of this in the staging option. You can control the number of cycles it takes the injectors to stage, the delay to come off stage, and the scaling factor which determines how much fuel the secondaries should supply in relation to the primaries.

 

Thanks for the replies guys. I'm starting to get a more complete picture now!