How can porting the plenum really improve anything on a carby-fed SC engine???
Think about it.
The air that has been compressed into the plenum is now above atmospheric pressure, and will therefore FORCE itself out the first available hole(s).. porting will have a good effect on a naturally aspirated engine, where the air is being pulled thru by the vacuum created by the moving piston... porting reduces resistance in the flow of air, therefore allowing more air to be sucked thru.
Still dont undrestand?? Try this....
Using a vacuum cleaner, first turn it on, then put your hand over the end of the pipe... the motor starts to strain badly cos you are restricting the available air flowing at negative pressure (vacuum).
Now put your hand over the exhaust hole of the vacuum cleaner... does it slow down? Hardly. Why? Beacause the air flow has positive pressure behind it. Positive pressure does not lose its efficiency with the same restriction (in this case, your hand). It is under pressure from the fan on the motor, and will therefore force itself out of the hole.
Sure, porting the plenum may help a TEEENY bit, but in this situation we WANT square edges to introduce turbulence into the air flow. This is to help re-atomise the fuel after it is compressed by the blower.
Square edges are a good thing to have in a carby-fed "suck thru" setup.
Flowing the plenum may be good on an EFI supercharger setup, where there is NO fuel in the plenum's compressed air. But it still wont do heaps.
If I am wrong here, please, shoot me now.
now I know