That said, most of how the Eastwood video presented porting, shouldn't be taking anything away from a street ride or "streetable ride". This was also in my first article:.
Streetable ride approved technique:
Reducing the machinist ridge in the combustion chamber in his example wasn't aggressive enough for me, because those create turbulent air. This is something that won't take away for a streetable ride.
Streetable ride approved technique:
The smoothing of the casting down to 80 grit sand paper? That's perfect from what I learned from David Vizard's book on this subject. The tiny imperfections and roughness may pick up carbon, but that'll happen anyway, you might as well have a desirable roughness to create small vortices, which make small roller bearings to make for faster.
Another item I disagree with on Eastwood's video on my last article, is that you should have spare valves that go in to protect the valve seat while you remove machinist ridges. That way, you can get right in there, next to the valve, and make a trench and then smooth that out.
Here's an example picture of the areas in question for a machinist's ridge: (be sure to click on the another article of mine. It has a lot more pictures, and when you click on them there, they get bigger; head gasket)
Port and Air Flow Theory III
A couple of points of re-study for me since video I made and embedded above, as this subject can make me feel left wanting again and again......David Vizard says that focusing on the points of the most restriction will make a port much more efficient. While hogging out a port where the air is already the slowest is likely to make a port simply lazy.
Back cut valves, rolled valve seats? Huge. It's been a while since I was in his book instead of on YouTube where I couldn't see the charts, but he made an example of how much air had to get past valves. In the picture, most of it is air, and beside it, is a little man to scale for how much air goes through a particular race engine. Yet, of course, still, there is that little valve, which is smaller still than the man when you see the math for how much "surface area" an imaginary cylinder from the valve seat to the cuts on the valves. That little sideways space, where all the action has to take place. Can you imagine it?
What is next to that moment of greatest restriction is often a machinist ridge in the combustion chamber. Most people won't touch it. The trick is to have a set of valves you don't care for as a guide to your single cut burrs, and round out a small trench around the valve, exactly the size of my smallest burr. Then blend it. Surely, everyone's fear is you've made the combustion chamber bigger! The tiny drop in size, vs. having air and fuel tumble and bounce through this section, which forms larger droplets, is more my worry. Plus, with the increased flow, while static compression is slightly lower, dynamic compression will be higher.
Make effort on the port side of the valve, working in the bowl ... I'll continue my thoughts on this at a later time. :)
Source: DON'T POLISH when Porting and Airflow Theory III by DENichols
By AutoBravado
