Vicoor

I've been thinking about the injector staging event, and I wonder if having the secondary injectors in the irons and primaries in the manifold would help to smooth that out.

My reasoning is that the primary injector would have the manifold wall wetted out, allowing that extra fuel into the combustion process. And the short distance from the secondary injector would allow for quicker recovery of the proper mixture when the secondaries come on.

The issues I foresee would be tuning the idle and transient response with the primaries so far up in the manifold, as well as possible emissions issues.
another problem could be adding the larger amount of fuel to the smaller air stream

Has anyone else tried this? What do you think?

Vicoor

I figured someone would have some experience (or at least an opinion) in this matter.

Monkman33

iTrader: (28)

The further from the port, the harder it is to tune idle. For vehicles that run a higher idle or are not as concerned with low rpm idle and low rpm drivability, no injectors in the primary location is fine. And much of the issue may be tuned out if the spray pattern and atomization are optimal.

The further from the port the injector is, the more time the fuel has to cool the charge, and atomize (as for soaking walls, this is why you don't port to a mirror finish) Larger injectors tend to benefit from being placed further upstream. Of note: the further upstream an injector is placed, the more important injector timing becomes. Unless you are spraying steady state, you run the risk of partial fuel pulse width consumption. This can cause other issues. Also, the further upstream an injector is placed, the less likely it is to idle well. Will the relatively short distance between stock primary and secondary locations make much of a difference? Maybe, maybe not. Variables include your specific engine and porting, injector size, timing, spray pattern, intercept angle, etc.

The closer an injector is, the easier it should be to tune idle in vacuum and non boost areas. Smaller injectors tend to be able to atomize quicker and tend to have better spray patterns. Intercept angle becomes important in this instance due to the relatively short amount of time from fuel pulse to passing through the port. The stock diffusers were intended to alleviate this, especially when we consider the difference in injector technology from 1991 to today.

Everything is a trade off. The staged injection was meant to be the best of both worlds.

These are generalities, and there will always be certain engine setups that vary from the norm. So your results may vary.