| Ernest,
With my current setup, this p-port engine idles better than my side-port motor ever did. It will idle down to 750-800 rpm if asked, although I normally idle at 1500-1600. Still, it might be an interesting experiment to add temporary dividers in the airbox to see what effect it would have on tuning.
If you take a close look at the picture I posted you can see the blue fuel rail. This is the primary fuel rail feeding the primary injectors. They're located downstream of the butterflies, very close to the intake ports and pointed directly at the rotor faces. I can't imagine how the fuel could find its way 18" back down the runner and back into the other runners. I've never found any residual fuel in the airbox either. I don't see how the fuel could be pooling so close to the ports, especially at 4500 rpm. But then I'm not an expert in fuel injection design either.
Alleviating fuel pooling in the runners was one of the design goals with this latest intake. My previous slide throttle had both the primary and secondary injectors located upstream of the slide. This caused fuel pooling, especially at very low throttle settings. Needless to say, this made low throttle tuning almost impossible. So, the new intake has the primary injectors downstream of the butterflies, and it idles great.
Mark
On Tue, May 29, 2012 at 4:32 PM, Ernest Christley <echristley@att.net> wrote:
Mark Steitle wrote:
> Ernest,
>
> I don't understand how that could happen if my injectors are after the
> airbox (see attached pic).
>
> Mark
At idle, the intakes coming off the airbox can set up some serious standing waves that will suspend fuel droplets and
let it stick to the walls. You're set-up is very similar to mine, in that the fuel can run downhill and air has to pass
in front of one runner before reaching the others. Some of that suspended fuel will coalesce on the wall and drivel
down the runner, and any coming out of the middle will get pushed back to the rear (which will then be running over rich).
It would also be interesting to watch individual MAPs across the runners. Dollars to donuts that the first runner's
inlet is at a partial vacuum compared to the rear one.
I may be wrong about the mechanism, but I know my fix fixed whatever was wrong. I inserted a plate so that the runners
could not "see" the air intake. The air hits the plate and spreads out before heading to the runners directly, instead
of flying past the first on the way to the second.
Going off of what I think I know, I would use a handsaw to cut a slot halfway through the plenum between the runners.
Then I would slide a partition between them. It would essentially create three stalls that the runners originate from.
The point being that air would not be able to go past one runner on the way to the second.
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