If you want to tinker and do a few things to make the motor breath just a bit better and perform a bit better there are a couple of things you can do. Just keep in mind that you will never get these early style heads to breath really well. You can only get them to breath a bit better.
The exhaust valves can be enlarged to 1 5/8. Use a decent small block Chevy exhaust valve, they are the same. Hog out the valve bowel a little bit. Not too much, just a little larger. Three angle valve job and Blend and polish a bit. On the combustion chamber side, in the exhaust valve pocket. If you run your finger down against the far wall, you will feel a slight little bump. Flow stalls at the bump, about .300 lift. You will have to relieve and slightly unshround the pocket anyhow for the larger valves. Take this bump out and smooth the wall.
Intake valve side, use an intake for a 50-52 powerglide equipped 235. It’s a 1 15/16 valve. Same routine as the exhaust. Three angle valve job, hog out the bowel just a little, blend the cuts and polish. Do a little polishing of the combustion chamber. Don’t get carried away, just a little smoothing.
On the intake port side of the head, you can carefully machine down the casting bump that helps hold the intake manifold retaining rings. Don’t go crazy here either. Install the rings and to the extent the casting is beyond the rings, grind it down. If using a new style Clifford intake 2x2, you can remove the retaining casting entirely as the Clifford does not use retaining rings.
You can polish the ports if you like. Again, no craziness here.
Headers, I love headers. I love how they sound. I have cut outs for mine and run them open once in a while. I have a pair of Clifford long tube style headers on my motor. I bought them in the early 80s when jack Clifford was still living. After he died, the fellow that was building all his headers disposed of jack’s header patterns so no more long tubes. But they do sell a shorter style true tube header. Not cheap but a real header. Other wise the Fenton’s or similar cast iron header. Me, I would stay away from those cheap headers. The design is not so hot, they are not true headers, and they are cheap and look cheap. Get something decent, you will be better off.
With a stock head, I found that they tended to run out of air around 4500 rpm. Some heads that I have run would not even breath that deep. With the above mods, my 261 head breaths up to around 5500 rpm. You can actually feel the motor run out of air when you get near 5500-6000.
235 Chevy rods are really only good to about 4800 rpm. I have run them as high as 6000 but don’t any more. 261 rods are a little bette. I have 302 gmc Rods in my 261. They are a lot of work and require custom pistons to use. But those are good to 6000 rpm or slightly higher (but no real benefit going that high, the head can’t breath that deep.
So if you want to tinker, go ahead. Have a ball. I do, I tinker incessantly with these motors. Do dive right in.
