Randy,
these velosity stacks are for my plenum box that will bolt to my Sissel 12 port head.

I would not recommend going to a 4" bore,walls are too thin.

Douglas's car(orange one) is for drag racing,normally aspirated.
He is not going w/a 4" bore for his turbo charged race car (yellow one).


MBHD


12 port SDS EFI