SM Head Modifications on a budget
Where the yellow is, it would help to lay this back to the gasket line, and concave the chamber wall from the deck to the seat top. I also don't do my seat cuts that way, but making more room for the valve will help...it will also speed up the air so that will make the pinch and ST more critical. But I've seen 280 cfm from a very mildly touched ST, large pinch, 89.5% throat, 75/60/45/38 seat cut with a back cut on the valve. No guide boss slimming, very little head bolt bulge work, but good chamber work and proper blending of the valve job especially on the ST side. You have to not just eliminate the 75 cut, but work it in a way that makes it more of a radius into the 60. The rest of the circumference I leave a small partial amount of the 75 cut and underneath it needs to be smooth. If you lay back the top of the ST some and blend it you'll hit 280cfm. If you want to show people how to get good ports, you need to start with the WHY...in this case it's about unlocking the short comings of the port to make it more homogeneous top to bottom. Opening the pinch with all this other work done, will slow the air down and allow it to better navigate the ST. But it needs to be worked really well...roof, common wall, floor and pushrod side as much as possible. Even on a smaller 340 this makes really great power. Now keep in mind, the port will be too fast just on it's own on your bench...but if you put an intake manifold on it and bolt the carb on it you'll see why, at least on the sb mopar, a fast port is not always wrong. I won't say the FPS numbers I shoot for but you can make the port too fast. And almost never too slow!! Hope this helps, if you guys don't want any further input I'm OK with that and won't hurt my feelings ;-)
Where the yellow is, it would help to lay this back to the gasket line, and concave the chamber wall from the deck to the seat top. I also don't do my seat cuts that way, but making more room for the valve will help...it will also speed up the air so that will make the pinch and ST more critical. But I've seen 280 cfm from a very mildly touched ST, large pinch, 89.5% throat, 75/60/45/38 seat cut with a back cut on the valve. No guide boss slimming, very little head bolt bulge work, but good chamber work and proper blending of the valve job especially on the ST side. You have to not just eliminate the 75 cut, but work it in a way that makes it more of a radius into the 60. The rest of the circumference I leave a small partial amount of the 75 cut and underneath it needs to be smooth. If you lay back the top of the ST some and blend it you'll hit 280cfm. If you want to show people how to get good ports, you need to start with the WHY...in this case it's about unlocking the short comings of the port to make it more homogeneous top to bottom. Opening the pinch with all this other work done, will slow the air down and allow it to better navigate the ST. But it needs to be worked really well...roof, common wall, floor and pushrod side as much as possible. Even on a smaller 340 this makes really great power. Now keep in mind, the port will be too fast just on it's own on your bench...but if you put an intake manifold on it and bolt the carb on it you'll see why, at least on the sb mopar, a fast port is not always wrong. I won't say the FPS numbers I shoot for but you can make the port too fast. And almost never too slow!! Hope this helps, if you guys don't want any further input I'm OK with that and won't hurt my feelings ;-)