This confuses me a little bit ----I'm looking for guidance on when to make the throat the smallest, or when to violate this rule and let some other section of the port be smaller. I'm currently working on a head with a 1.88 intake valve head---your software suggests a 1.634in2 port CSA with a 2.239in2 throat. I look forward to your wisdom on this.
on the Chevy SS 362 at 7200RPM with 1.948 area and 1.940 OD Valve
the reasons the FPS is faster in the Port than at the Throat,
1- the #041x SBC Head is only 165 CC
Port_Vol_CC = CenterLineLength * CSA * 16.387
164.97 CC = 5.168 * 1.948 * 16.387
NHRA = 165 CC max
1.948 SqInch Area is PipeMax recommended
"Smallest Port Area" ...and thats what it is at approx 165 CC's
the FPS Speed is faster in Port than Throat area due to 165cc limit
2- the GM designed Port Shape, 23 deg angle , location of valve
relative to Bore Center @ .500" Lift, etc...all factor into how much
CFM this design can achieve and still remain at 165 CC and pass
NHRA Tech.....so what happens is the VE% and the CFM/SqInch of Valve
Area is much lower than a modern ProStock Head,
and the Velocity FPS is slower at the Throat
The VE%= 104 or so
3- the 1.940" OD Valve is capable of Flowing a greater amount of
CFM/SqInch than it shows in the #041x design.
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on the 500 cid ProStock example
the situation is sort of opposite than the SS362
the ProStock Heads are modern "unlimited" design,
Heads flow a higher CFM/SqInch of Valve Area number
along with higher VE%,
so the Velocity FPS is higher at the Throat than the Port
so a high flowing Head, with great Ve%, and with a relatively
smallish Valve will show you more Throat FPS than Port FPS
if the Throat FPS is too much faster than 311-330 FPS or so,
its beginning to show the Valve OD might be too small ?
i don't think any "fast" top running 500 cid ProStock Engine
is running a 2.430" OD size Intake Valve ??
that would be about 350 fps @ Throat
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I'm currently working on a head with a 1.88 intake valve head---
you might look at the included PipeMax File => CHRY_360.PMD
thats a NHRA SS360 with a 1.880" OD Intake valve
OEM CenterLine Length approx = 4.948"
in Ported/Epoxy Form a little longer "internal length" than OEM
NHRA max= 162 CC
OEM 156.6 CC = 4.948" * 1.931 CSA * 16.387
so in ported Form, closer to NHRA limit of 162 CC's
in that Head it shares the same limits/problems as the Chevy #041x
its also slower FPS at the Throat
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in your particular application,
it just depends on a bunch of relative Factors,
as to the achievable Throat FPS -VS- Port FPS
if your Heads are great modern designs,
you will probably achieve higher FPS @ Throat
and vice/versa
----I'm looking for guidance on when to make the throat the smallest, or when to violate this rule and let some other section of the port be smaller. I'm currently working on a head with a 1.88 intake valve head---your software suggests a 1.634in2 port CSA with a 2.239in2 throat. I look forward to your wisdom on this.
