cleaning up the slant six head
Typically you don't go more than the aforementioned 3/4"-1" deep into the runner in either the head or either manifold.
Extrude Hone is good for dry flow (MP-EFI), not so much for wet flow (TBI/Carb) because it lacks the surface finish to keep partly atomized fuel in suspension. Same reason that you don't polish intake ports. I suppose that you could use a heavy grit and sand-blast after Extrude-Honing a wet flow intake. Sure seems like a bass-ackwards way of doing things, but it might have some merit.
No one seems to recognize the extent to which the cylinder HEAD is the bottleneck in this N-A deal. Putting headers or a ported intake on an engine that already has such an egregious breathing problem that originates in the HEAD, id like putting a band aid on pancreatic cancer; it won't do much good.
The logical choice to making power out of this strangulated non-breather, is a nitrous oxide system, or same sort of forced induction. It's a shame that the engine was designed with such small bores, but there it is.... and they preclude any sort of effective flow-increasing efforts as regards changing the ports/valve setup; there's just not enough room.
However, the incredibly stout infrastructure of this engine makes it a really good platform (in terms of reliability and output,) for alternatives to asking this thing to breathe, naturally-aspirated.
It never will... :disgust:
All the well-meaning speculation in the world won't help you make even 1.5hp-per-cubic inch out of this unfortunate example of poor air-management. At best, you might get 300 horsepower, after massaging every aspect of the engine's port/valve/manifold/cam/piston systems... and at what cost?
Not a good candidate for N-A exercises...
Just my opinion... nothing more.
