mechanical constant flow injection


The Grumpy Grease Monkey mechanical engineer.
Staff member
just a few ideas to think through,
We know that air weighs 14.7 psi or pounds per square inch at sea level – meaning about 15 pounds are pressing down on every square inch of you.
now consider that stack injection tube and intake runner length and head port, combined is anywhere from maybe 15"to maybe 23" measured from the rear of the intake valve to the stack entrance bell. now consider the internal stack diameter on various intakes might be 2.75"-3" in diameter, thats between 6"-7" square inches of area thus you have maybe, 95 lbs of air mass trying to force itself, through a roughly 4 sq inch valve opening 2.25" dia. valve times the RADIAS squared tines PI.
in each of 8 intake runners.


then consider that properly timed cam and header exhaust scavenging can easily triple the intake draw and increased flow rate and you get to see where a properly set up stack injection set-up has noticeable benefits, especially when the stack injectors spray fuel at the back of the intake valve area so the air flow in the stack is not slowed by the necessity to drag fuel nor it there a pronounced tendency for fuel to drop out of the air flow path like there is in some intakes with twisted runner designs


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The Grumpy Grease Monkey mechanical engineer.
Staff member

I was recently asked why I did not select the cross ram version of the BBC mechanical injection?
well it looks great but to get the intake runners cross over to fit, correctly a compromise is required.
the internal port size cross sectional area, must be reduced to the point it limits air flow ,
that reduction in port cross
sectional area, well it basically knocks more than a 100 peak, peak hp off ,
compared to the BBC vertical stack injection configuration
that might not be easy to visualize,
but its obvious when you place both intakes side by side, and even kinsler will point that out.