So I ported and half relieved my 1953 8ba block. I made my intake ports rough so the fuel tumbles in with the air. That what my boss said to do. It makes better atomization. I polished all the valves and all of that. Now I relieved it. But I was wondering if I should leave the relief rough or should I polish it out and make it smooth? And btw I will be using a 2 or 3 deuce intake with sharp high compression heads. Sent from my iPhone using H.A.M.B.
No...he really didn't say what the block is...but we can guess by his avatar..! I port overhead valve heads, have for 30 or so years. Only done two flat head blocks. On the first, I left the surface smooth, but not polished. The second, years later, as I do in over head intake ports, is to let a carbide cutter kind of lightly bounce on the surface, making tiny little craters. That is, guide the cutter over the surface after final shaping, but do not use any downward pressure on the iron surface. What your "boss" said is sorta correct. While it does not make the "atomization" better...it does help to make sure that at low air/fuel flow speeds (low rpm), fuel droplets have a tendency to stick to polished or smooth surfaces, then when you hit the throttle, the big drops are forced off of the surface by the new higher flow speed and end up in the chamber as BIG drops...not good. You want the smallest droplets as you can get. This is why modern fuel injection is good, the drops are VERY small. Small droplets ignite easier/faster than larger drops to make better power. Like 60 or 40 grit sand paper surface vs. 600 grit paper surface. 60/40 grit surface good, 600 surface, not so good. Mike
I would think that you want the relieved portion of the block (down stream of the valves) smooth (if not polished). It is part of the combustion chamber and you don't want any hotspots. My flathead was factory relieved...and it's smooth.
Listen to Carl (reply #9). Work your way backwards from his thread > https://www.jalopyjournal.com/forum/threads/flat-fed-build.436556/page-82
Mike and Carl are talking about the ports. The question was what to do with the relieved area inside the combustion chamber? I'd say make it smooth. Less chance for any build up of carbon. The underside of the heads should be nice and smooth too, if you want to go to the work.
On a street flat head you probably will never tell the difference. But in your head you will be convinced. Enjoy
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