Relocating CIS injectors for more power....

[PowerDubs]

After talking with a friend, we are toying with the idea of essentially spacing the injector housings to move the injector tips back out of the middle of the intake manifold/port where we are pressuming they are causing a considerable air-flow restriction at high RPM (up to 7500+)

Since this is a constant injection system, and the fuel basically puddles on the back of the valve until it opens anyway, we can't foresee how this would hurt anything. The spray pattern and cone is plenty strong enough to spray this extra distance.

We are guessing, at worse case, this may make idle slightly rougher and possibly screw emmissions up possibly?


Ideas? Suggestions?

 

[DEngler]

Yes, the injector (really the fuel pump) is powerful enough to spray the extra distance. The problem is exactly that which was solved by locating the injectors close to the valves. Fuel film area. By moving the injectors back, the fuel film surface area increases. This would be fine if the fuel would evaporate proportionally with the surface area, and it does. But since very very little (almost NO) fuel evaporates from the fuel film, the evaporation it is not enough to make up for the increased volume of fuel in the "puddle". In steady state operation, the puddle if filled at the same rate that it drains into the cylinder, but during transients (changing throttle position) the air has no problem with acheiving a newer steady state while the fuel puddle takes a few seconds. The result is lean mixture while transferring to acceleration and rich mixture while transferring to deceleration. Reducing the puddle volume helps this, and with the CIS, the large intake air volume from the injectors to the air flow sensor compensates enough that no acceleration enrichment is necessary. This is a common trait of port fuel injection.

If you really really are having air flow problems because the injector is in the way, just move it out of the airstream, but keep it close to the valve.

 

[Marquis]

DEngler
Interesting, I hadn't thought about this aspect- the proximity of the injectors and how it effects evaporation during transients.

Can I infer from what you are you saying that generally the closer the CIS injector to the intake valve the better the transient fueling?

If so could you please take a look at this thread and comment?

http://www.eng-tips.com/viewthread.cfm?SQID=66813&SPID=71&newpid=71&page=1

Bascially I want to mate port throttles with K Jetronic and am worried about transients, but if Injector proximity is a varaible I can vary this and area compensate the port....

 

[PowerDubs]

I've seen kits on ITBs that run a 'high-mount' secondary set of injectors in the horns for more power at high rev...no one has any experience?