DIY_EFI Digest V4 #214

[Fran and Bud]

THOMAS,
>From what I have been able to glean from various sources, the location of
the injectors ABOVE THE THROTTLE BLADES is a design feature of TBI.  The
injectors intentionally wet the throttle bore walls and the throttle
blades/butterflies much of the time.  

Find a friend with a TBI and watch it run with the air cleaner and spacer
removed.  You will see accumulated sheets of liquid gasoline on the blades
and on the walls - moving slowly toward the outer edges of the blades. 
Their appearance will remind you of water movement on the hood or on the
side window as you drive in the rain. Your car is moving through the air at
60 mph but the water is moving on your hood or window very slowly (boundary
layer).  You will see the gasoline move along the walls and throttle blades
in the same manner. As the gasoline reaches the  narrow opening between the
blade and wall, it is torn off and mixed with the air flow which is
travelling at sonic velocity when running at idle or part throttle (cruise).
The mixing is excellent and distribution is very uniform. Idle and part
throttle operation are excellent as long as the pressure drop across the
throttle opening, and the corresponding air velocity past the edges, remain
high.

WOT is also good - due to so much air mass passing through the injector
spray.

The biggest problem with TBI is when the intake manifold re-pressurizes
rapidly (pedal to the metal) resulting in fuel condensation on the intake
runner walls coupled with air velocity that is too slow to harvest it. 
Cleans itself out as rpm comes up and air flow increases.
I have also been told that this is one of the reasons that factory TBI
manifolds have so much space devoted to passages for hot water - helps the
air stream to regain the lost (condensed) fuel. 

Like most of the stuff you will read on this (or any) list, some of the
information is correct and some is less than correct.  The trick is to
accumulate and digest as much as you can, then think about it and draw your
own conclusions to fit your own needs.  My opinion is that you cant go wrong
putting a GM TBI on your Cutlass, and do it as close to the way GM intended
it to be done as possible. THEN FIX IT to suit yourself. 
BUD
 
>From: Thomas Martin <marttj at pcmail.css.mot.com>
>To: diy_efi at esl.eng.ohio-state.edu
>Subject: Re: DIY_EFI Digest V4 #214
>Date: Wed, Apr 7, 1999, 6:55 AM
>

>     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.
>

>