I haven't yet used the six pack but I plan to for my 318.
I have been told that the manifold is somewhat restrictive on any motor that sees the far side of about 450hp, I don't expect I'll ever see quite that kinda performance out of my 318 but a stroker is a different story.
I strongly believe there is as much potential in the six-pack manifold as any other dual plane, I am keen to do some porting on mine before I install it.
The 440 and 340 carbs have the same bolt pattern and layout.
both systems are equal to about an 880 CFM four barrel carb. There is no additional airflow in the 440 six pack carburetors, they are just tuned differently. Both will most likely run lean on a modified motor.
Promax make metering block and plates to allow the factory six-pack carburetors to take Holley jets and be tuned just like any other Holley carburetor. (without these, tuning is a said to be a nightmare)
They also sell a throttle plate that has the idle air bleeds angled outwards for the rear carburetor, this allows adjustment without having to remove the rear carburetor from the motor.
Hope this helps
