Forgive me for being obtuse, but with the limits of the 3 port head, wouldn't it make more sense to hang a blower on one instead? I understand, and applaud the efforts of trying to eeek out as much power as possible with a porting tool, butis it really worth it? Just asking...
...dawg
Defining what these limitations are and what can be done about them is what interests me and finding someone with a flowbench willing to evaluate it has made for some interesting learning.
Here’s a new year’s update:
I dropped off a head with the following intake modifications as well as 1 polished/enlarged exhaust port for testing:
Manifold side opened to 1.44” (cylinders 1,2,3,4,5,6)
Guide tapered 5 degrees (cylinders 1,2,4,6)
Bowl opened to 1.57” max. (cylinders 1,2,3,4)
Bowl flared to seat 1.57” to 1.63” ” (cylinders 2,3,4)
Short side radius changed from 1/8” to 3/4” (cylinders 3,4)
Roof blended to remove guide boss (cylinder 4)
The modifications were visually inspected while I was there and his concern was that the poor intake/exhaust flow ratio is only going to get worse with intake improvements and the exhaust needs help for real gains. I reworked one exhaust port by hand pushing the roof up 1/16” and polishing smooth so difference there will be documented but is not expected to make a huge improvement. Facing off whatever reasonably possible to reduce chamber volume and then generating an improved radius everywhere the combustion chamber overhangs the cylinder has been suggested as well as some unshrouding in the tight corner behind the exhaust valve by means of a radius divot. With the exhaust valve positioned deep in the head it will allow for a cam of longer duration to overcome what is lacking and now I understand why the dual pattern cam was going in the right direction. He showed me his cam design software, grinder, and collection of masters and does custom cams regularly so more options are available to explore.
Since then I milled .072”from the deck surface on another head which fully removed the depressed area of the chamber between the valves. After this the intake valve was sticking up .030” on what I believe to be an original and not reground valve but with a head that has been reseated at least once (.015”?) so zero decking should still be possible. When I mentioned recessing the valve the same amount of the facing he looked at me strange and said he would never do that as it discards compression and would correct it by shimming or replacing rocker stands or custom length pushrods. In a few weeks I should have some more numbers and chamber toolpath for testing.
