Picture of 340/360 head porting....Mistakes?

PRH said
More armchair quarterbacking.......

Imo...... you haven’t taken enough off that lump in the roof next to the guide boss, in the head bolt area.
That material needs to be completely removed for the “high effort” type jobs.
Along with more material removed behind the guide, making for more of a “boat tail” type shape.

View attachment 1715469745

I agree 100%. But we both know that is a massive bunch of work. And we both know grinding sucks, and grinding cast iron double sucks.

If you want the power, you need to do the work.