Ford race 4 cyl (DBA ??) used a stainless-steel
shroud that you slipped onto the valve stem
in the bowl-area before you final assembly of the head
some racers said it worked and some didn't
no dyno data
it supposedly picked up bottom-end torque
with sacrafice in top-end performance
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Vanes on the port floor or short turn are usually
result of flowtesting bare ports "WITHOUT" headers or
intake manifold attached as well ...so what happens
is in a live engine , floor vanes hurt HP / Torque
at high RPM
GM did this with the 1st D-Port BBC heads ,
supposedly all developed on FlowBench , but never
backed-up in dyno test -vs- with or without vane
in exhaust port floor , but at that time ,
it was left in production, ... and ProStock / Comp
used the vane to attach welding to, building the floor
upwards till flat without vane effect, along with
raising roof with or without exhaust port plates !
--so what wound up as a BOO BOO , worked out OK in end.
like GM BBC D-Port , other times vane in port floor
short-turn area picks up the flow on a flow bench,
but its false flow, and the engine was really responding
to increased velocity in that area and not the actual
flow gains.
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another example is the NHRA SuperStock Chrysler 318-340-360
engine .... before NHRA let any valve shape be used ,
the stock Chrysler intake valve was a Tulip-design,
it hurt low to mid-lift flow numbers , but high lift were OK
after NHRA allowed any valve shape , we went to a nail-head
design with backcut angles, low to mid-lift numbers
increased with high lift numbers the same as before with Tulips
on the dyno, the Tulips made torque sooner , come on the cam sooner,
with the nail-head valves, torque began later, but wound up as much
peak torque and with a little more Peak HP , but higher by 200 RPM
Actual DragStrip runs were faster with nail-head after rear gear ratio was increased
to compliment .....than was with Tulip valve head
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Sort of what Bill Jenkins was trying to describe in his book
and also what Phillip H . Smith's
"Scientific Design of Intake and Exhaust Systems" =>where when the
intake flow was too good for low RPM airflow demands,
you lost too much ram effect at end of stroke.
You got it back as you reved the engine higher if cam timing was OK
you won't have this effect or problem with EFI
EFI frees up the headporter ...you can make a port too big and
not pay a penalty with EFI
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and David Vizard being an Englishman ,
would have been very familiar to Ford's English Race 4 cyl
with shroud insert
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
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