The header flanges I purchased from Speedway Motors pn# 418-1142. They are 5/16 thick.
http://www.speedwaymotors.com/
I will be running MPG port plates in my 4V heads. The purpose of these plates is to raise the port floor to increase velocity. The problem with the port as cast is the drastic drop off after the short side radius.
It didn’t make sense to me to spend money to correct a problem only to re-introduce it again at the header flange with a drastic drop off into the tube.
Here is the difference between the plates and the flanges.
I went to the Hardware store and bought some square key stock. I then cut it to the shape of the lower opening in the flange.
I then fit them individually into the openings. I made them a little lower than the port plates to that I didn’t have to flatten the bottom of the tube to fit the opening and it allowed for a good transition. At the time the Hardware store only had 3/8 square stock so I had to grind them to fit the 5/16 thick flange.
Here they are all welded up. I will be running a 4V sized header gasket. The opening is below the weld so there won’t be any problems with leaks.
