DIY_EFI Digest V4 #214

[Walter Sherwin]

>     Has anyone pondered the idea of TBI injection with the injector spray
>     BELOW the throttle body?  Does it NEED to be above?  It seems to me
that
>     it would be messing up the atomization running into the throttle
blade.
>
>     Have the injectors able to spray down the runner to the port?  Or is
this
>     far more trouble than anything you could gain?  (like go with
sequential
>     port)
>



Accel have a setup exactly as you describe.  4 barrels, and one injector
below each throttle blade.

The *injection above* style TBI systems take advantage of shear and
turbulence around the sharp edges of the blades, to mix and homogenize the
fuel/air charge during low to medium airflow conditions, and work pretty
well.  At some throttle openings, you can get fuel bias towards one set of
cylinders or another, as the blade can act as a big "paddle".  Unless you
are using the big 52mm 454 TBI, this is typically not a huge problem.

The *injection below* systems rely upon the injectors to atomize the fuel.
At high airflow, this works well.  However, at low to medium airflow the
injector spends a lot of its time "wetting" the opposite wall (manifold or
throttle bore) and can introduce part throttle driveability problems.

Both systems work, but if you need good driveability and part throttle
"snappiness" then I'd stick with the *above injection* systems.

Walt.