primaries and secondaries (n00b question)
 

okay i searched and found out nothing, apparently everyone but me understands this already, but why do people use like 550cc primaries and 800cc or 1600cc secondaries? does the stock setup use two sets like this? if not, why not just replace the primaries with really big ass injectors? i know its a dumb question, but i would really like to understand this. and does it matter what sizes you use for primaries and secondaries as long as the net volume is the same? ie. 500cc primaries and 700cc secondaries OR 700cc primaries and 500cc secondaries (random numbers)

To the best of my knoledge, the reason the rx-7 has two sets of injectors is because at low speeds you don't need as much fuel. As the intake velocity speeds up at higher rpms the secondaries, which are farther up the intake path, allow the fuel more time to atomize.
Feel free to jump in if I'm wrong, but I think thats at least part of it.

You want to run the larger injectors in the secondaries. If you run larger injectors in the primaries with the stock ECU than you would flood and won't start or idle really ruff. The secondaries come online around 3600rpm.

Stock T2 is 550's all around. I run 550's in the primaries and 720 in the secondaries.

so thats why people dont run 720 primaries without an rtek...that makes sense. can the stock ecu handle anything bigger than 550 secondaries?

Well, technically the stock ecu alone cant handle anything but stock injectors. You can get a piggyback fuel controller like the SAFC and you can run larger injectors with the stock ECU. When you get to huge ones like 1600's, though, you have to go to a standalone.

The stock ECU for an n/a really shouldnt have to control anything bigger then 460cc. Same with a stock ECU for a Turbo. But you can get by adding larger injectors as long as you have an SAFC or Rtek(turbo) atleast since you would probubly need to turn them down a bit in the low end and idle.

you need to give someone else the gas bill

ok.. iu have a quick question then tool.... wut r the horspower caps on each injectoru size sets? i have the stock 550's all round, how much horspower can i saflet have or howmuch boost can i run before i need to up the secondaried form 550's to say 720 or 1000cc injectors?

I would be careful running more than stock boost with the stock injectors. It all depends on what your running what is your goal for the car, but if I was running more than stock boost than I would upgrade the fuel pump and up the sec. inj. to 690's or 720's and some kind of fuel control.

I'm running 720 secondaries with a Hybrid turbo on 10-11psi and they are close to maxing out. Dynoed at 294 horespower AFR's where around high 10's to low 11's.

Its better to have to much fuel than not enough. So I'll be going bigger when I get the chance.

This inspires me to ask the question: since the secondaries atomize better/longer w/ a standalone could you just use secondary ports? or is the slow air velocity at idle not going to allow the fuel to atomize at all?

its not the speed at which the fuel atomizes, its how fuel can safely and contantly be atomized at one time...

you probably could, but it seems to me that if you get a standalone, you probably have at least 1600 secondaries, and the price for anything bigger than that would be re-god-damn-diculous.

thats why you add another set of injectors

precisely