Jeff, you will probably get a number of views on this topic.
There are those who believe injecting the fuel nearer the TB (further from the intake ports) will give better mixing of air and fuel and more importantly more time for the fuel to turn from liquid droplets to vapor/gas therefore better efficiency. There are others that believe whatever mixing benefit you get you lose something because now there is a longer run with metal walls to cause the fuel to adhere to the walls and not mix as completely. Like most things probably a bit of validity to both views.
I have tired it both ways. I had a 75mm TB and four injectors sitting approx 18” from the intake ports. I could not tell if there were any increase in efficiency or power – there may have been but with the limitation of my instrumentation you just could not tell whether there was or not. It certainly wasn’t significant.
However, what I did encounter was if I suddenly opened the throttle, the engine would bog or hesitate – the engine never stopped, but I found that this used up more seat cushions on a go-a-rounds {:>). So I went back to putting the primary injectors in the block and secondary injectors as close as I could get to the intake ports. I personally like this arrangement. YMMV.
My 0.02 worth
Ed
Ed Anderson
All of that plus: Throttle body injection (became a universal term like Kleenex) was used early on, when GM and others couldn't bring themselves to buy a license from Bosch for electronic fuel injection, so they came up with a single big injector planted in the bottom of what they knew how to do. Build carburettors. So the throttle body and the (single big) injector were in the same place. Not as good as real fuel injection, and, not as good as a well tuned carburettor. And still GM went under.
Now typical close in injectors (low and medium speed?) are now in the block or head casting and the out injectors (high speed?) are just a few inches out from the head. Now, the throttle body is dry and contains only an air control valve and some sensors like airflow and throttle position.
Lynn E. Hanover
Mearly 67 years young.
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