Well this manifold shown is actaully ordered up by the customer. He was a ford engineer and he knew exactly what lengths and cross section and plenum and everything else he wanted.
The trumpets are all radiused on the end but no bell mouths. We`re trying to keep cost at a premium here
The only way to get a bell mouth done correctly every time is mill one out of billet with cnc equipment. Thats upwards of 30K just for the machine. That isnt good for you guys buying this stuff. Regaurdless they flow well for not being expected to run on an F1 circuit.
I use software to determine the lengths and the widths. Basically I have commited to memory about what will work with what application. N/A is pretty tricky. Its alot of compromising but in general the software I use will get me within 5%. So if you ask for a peak at 6500 you might get 6800 you might get 6200 most of the time its about on though.
FI is very simple however. Big short and alot. The plenum size could be as much as 4L (200 percent) as long as your not concerned with throttle response. For the most part the fi guys should stick with what I do for the n/a people on plenum size. Short runners about 5 inches and a step up in inner diameter pipe. This is a good streetable turbocharged recipe.
And i can make the runners shorter and fatter and the plenums bigger for you power hungry fi guys. Im also working on 2.5L and 3.0L upper intake manifolds.
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If he/she has 50 years experience I would expect alot more. I can tell where they did and didn't use filler rod by the shape of the beads. That there makes for a weak weld 