Lets say the head porter has done his job correctly and the CSA(cross sectional area) of the pushrod pinch point is 2.4CSA. I understand that the valve throat area should be slightly less but that's the headporters job and that's why I paid him the big bucks to get that part right.

Now for my part of the work should I make sure that no part of the intake manifold is less than a 2.5CSA(slower air speed) and that the match point is say .015" less to alow for slop when mounting the intake to the head?

Reason for the question is that I saw on another site by a reputable head shop that airspeed at the valve throat should be fast, the bowl area slower, the pushrod pinch point fast and the intake slower. So fast, slow, fast, slow.

Any thoughts appreciated.

 

So fast, slow, fast, slow
from Bowls towards Carb

or from Carb towards Bowl
Slow, Fast, Slow, Fast

those FPS velocity descriptions are what you normally see sometimes
with Pitot Probe (23deg SBC)....its not the Best recommended progression.

there should always be "some" Taper in the Induction Path
and it would be nice to see
Speed FPS increasing as you move from Manifold Plenum Entry -towards-
Bowl + Valve Job + Chamber transition

sometimes you have to Slow-down FPS to get more Mixture
to Turn over the Short Turn Radius to present the Mixture Flow
to the entire Valve Circumference Area + Curtain Area

if the Short Turn's Floor velocity fps is too fast
it will look great on FlowBench CFM Numbers,
but it will make Less HP + Torque
and use more Fuel on Dyno,
accelerate slower down DragStrip.

you need "just enough" speed FPS to combat or fight off
the piston trying to reverse flow at the Intake Valve Closing point
in your desired RPM range .

to create speed FPS,
it always takes Energy,
so you want just enough speed FPS to do the Job in your RPM range,
any more speed, and you can cause HP + TQ Losses,
and Air/Fuel Separation...which just makes you use more Fuel
to make the same or less HP.

the Speed at the rapidly changing Curtain Area ABDC -to- Int Closing Point
is your last chance of high velocity to fight-off the Piston trying
to reverse Flow backout of the Cylinder into the Intake Port.

 

one more thing
you can only Calculate the "Theoretical Velocity FPS"
but that won't be accurate enough...

you need to actually measure the Velocity with a Pitot Probe

 

Print out anything information that Larry throws your way - pure gold.

 

Thanks !

Also,
the Intake Valve itself,
is rapidly closing towards the Seat,
so you have the Valve itself "moving" towards the incoming Mixture,
and the Valve is sort of blocking or fighting incoming Mixture
on its way to closing ABDC.....

better Low-Lift Flow at the Int Valve Closing Event,
is the only time i see an advantage of better Low-Lift Flow helping out.
That is..the "ability" of the Mixture to Flow around the
closing valve !

if everything is working great ,
you can have + 3 psi at IVC point ABDC
that will effectively make Low Lift Flow a bunch better than
you see on the FlowBench at 28" inches

about a 1.721 correction factor which makes
140.0 CFM @ .200" Lift on FlowBench @ 28"
then Flow
240.96 CFM @ 3 psi @ .200" Lift ABDC

which has a chance of greatly increasing Volumetric Efficiency %
Torque + HP

 

I'll second that! You can take his information to the bank...or the strip.

BTW, Larry Meaux is Mr. MaxRaceSoftware.

 

Thanks guys for the excellant information. It was going from the intake valve to the carb and fast, slow, fast, slow. The last slow being the intake manifold if I read the post correctly.

This application will be on a TPI system which I'm trying to greatly improve with a ton of modifications. The heads are Dart Pro One 200cc heads. It is the intake manifold portion that I'm now working on. It is a First Injection intake and it looks like a factory TPI on steroids. It can really be opened up.

So if I read Larry correctly I need to taper the intake as best I can from the intake runners to where it meets the head. Maybe a couple percent taper. Or to put it another way the air needs to be moving faster at the intake where it meets the head and slower where the air enters the intake from say the plenum.

I follow Larry and the gang on the "unmentionable site". Again thanks alot guys.

 

Or to put it another way the air needs to be moving faster at the intake where it meets the head and slower where the air enters the intake from say the plenum.

that's basically how all the Intake Manifold Manufacturer's including
Edelbrock have designed their Intake Manifolds over the years !!

next time you are on a FlowBench, use a Pitot and probe the Velocity
at the Intake Runner Entry in the Plenum.

or just use Snap Gauges with Dial Caliper and measure
Plenum Entry CSA -vs- Head's Intake Port Gasket Entry CSA

quite a bit of difference
in CSA and Pitot FPS Profiles