You know what they say, nothing ventured nothing gained. I like to tinker so I have ventured and done two intake manifolds. One for a 261 and the other for a later 250. They both worked, to what degree remains to be seen, but they did not fall flat on their face, lol. I built a 2X2 intake for a pair of Holley 2300 carbs for a 261. No one made a commercial manifold for that set up so I made one. It worked pretty good. It was pretty basic, kept the overall volume of the interior chamber down to keep the velocity up, used a shop vac, a plexiglass top (for mock up) and an old fashioned smoke bomb I bought in South Carolina at a fireworks place to look at the smoke flow pattern inside the manifold and shaped the inside to go with the flow so to speak, then welded the aluminum plate on top. It worked fine. I would not do the smoke bomb thing again, lol. Whether it worked as good as it could have if I had access to professional equipment remains to be seen, but it was fun and frankly that is all that matters because life is short.
Yes, getting a 235/261 head to flow is a near impossible challenge, particularily on the exhaust side, but there are a few things you can do to improve the flow. Just keep in mind, no matter what you do, it will never flow well. For example, if you run your finger down the far side of the exhaust chamber, you will feel just a little tiny bump/depression. This little bump causes the exhaust flow to stall at about .300 lift. So one thing you can do is use a piloted cutter and take the bump out, not too much, just enough to straighten the wall out. I also like to hog out the exhaust valve bowl just a little and install 1 5/8 small block chevy exhaust valves, and a little bit of relieving to take advantage of the larger valve. Might not make a big difference, but makes a little. I also generally like to hog out the valve bowl for the intake side and install 50-52 chevy powerglide 1 15/16 intake valves. Do a little hand blending and a little polishing. I occasionally will machine the bump in the head at the intake port (helps keep the manifold retaining ring in place) to either remove it (if you are running a Clifford 2X2 like I am the manifold does not use the retaining rings) or take it out as much as possible, and match up the intake manifold. I don't have any quantitative analysis to show what improvements if any those modifications cause, but my motors run pretty well, so I think they are helpful, but what do I know, I am just a backyard hacker at heart!
I have also done the bolt in lump port conversion for the 230/250/292 motor. Its a good project. You need a few tools, but you can do it at home. I own a sissal lump port head (a photo of it is in Leo Santucci's book. It was originally his head with epoxy lumps for a turbo application). Using some dividers, I traced both heads and the results are reasonably close. The lumps keep the velocity up after the bolt boss is removed, changes the flow pattern and improves the short side radius. Pretty fun project that you can definitely do at home with a few basic tools.
Last edited by Dragsix; 02/01/2018 2:23 PM.
