Opening up log manifold

[Bunji]

Has anyone opened up a Toledo single carb log manifold by boring or porting in order for it to be less restricted?

[cliftyhanger]

I doubt there are any serious gains to be had. It is a well designed manifold, equal length runners etc. Plus a properly setup single carb is within approx 2bhp of a twin HS4 setup on a (std) 1500. It can't be too bad.

[Bunji]

What about when swapping a single HS4 for an HS6?

[cliftyhanger]

I don't know how large the manifold is at the carb flange, but simply opening the manifold up there to match the carb should do the trick. Port matching the manifold to the head too. I would be cautious of doing much else, things often end up worse.
Power gains are going to be from headwork and cam. And probably decking the block.