I agree with you on the stall being low. What ever it is, it's going to be too low. I'm hoping I can see how the engine behaves and make a better educated guess on what stall to order than making a guess at this point.
I'm going to make another go at building my own headers. I have some 1.5" primary pipes that I thought are too small to use as a high performance headers, plus I have larger header pipe on hand as well as an assembled equal length header that has a larger primary pipe diameter, so didn't think much about using them. But now, given I'm trying to make a twin scroll exhaust setup, the guidance I've gotten was to keep the secondary pipe fairly small, so with that in mind I could keep the primary pipes smaller as well.
So the plan is to use the 1.5" primary pipes into two individual collectors, keeping them as equal length as I'm capable of, then run two 1.75" secondary pipes to the T4 flange, and again keeping them as equal length as I'm capable of. I have several 90º 1.75" bends on order to get the piping to the passenger side of the engine. I was going to simply have a local shop bend me up a few non-mandrel 90º's and plumb off the exhaust manifold, but I was getting the run around by the shop I was going to use. So I'm abandoning that idea until I get frustrated with these headers, lol.
When I digitized the exhaust ports to calculate the area, they averaged 1.82sqin, and 1.5" pipe should be around 1.77sqin, so fairly close. I'm going to keep the pipe tucked up along the top of the port as best I can and stretch the metal downwards from there. I believe there are two headers worth of pipes, hence the huge pile of U's.
