Porting, Using a Mill
Posted: Fri May 29, 2020 3:41 am
Hi all,
This is my first attempt at porting, other than matching ports and smoothing obstructions.
I have this old set of C6 heads that I got for free, about 10 years ago. They had screw in studs and a descent set of springs and retainers. Someone had done some grinding on the exhaust ports but not the intake. BTW, when I'm done, I won't use any of that stuff.
It will have LS, 8mm valves, cut down intakes, to 1,900 and the std 1.570 ex. Both with LS guilds installed.
So, with no money to loose, I decided I'd try my hand at re-machining the ports. What you see in the pictures, is a fixture I made to accurately hold the heads, using the guilds and the core plug holes, for height and angle plates (that's what also holds the spuds, in the core holes). BTW, those core holes are exactly the same height on both end of both heads. I think they may have been used in the tooling of the heads when they machine them at the factory. I measure those on my surface plate, as well as the guild C/C spacing. The guilds are exactly 1.82 C/C. As you can see the casting is very close, port to port, so there is almost no core shift, in these. The depth for each operation, is set the same for all cuts. I was impressed at the repeatabilty of each operation.
First I went though with a 60° cutter, opening the throat to 1.83 on all intakes, then I took a 1 1/2" ball end mill and took it to a depth that I felt comfortable with and took out most of the guild, it leaves a very nice look at the built in swirl pattern in these heads. Before I finish the intake bowl, I have to make a 75° cutter, to blend the 60° to never the bottom of the bowl. then blend it all together. From Carnuts thread, I know to be careful with the SSR and I won't try to lay it back, just make the biggest radius I can. The length of the 1/2" LS guild, that protrudes into the port, will be shaped to match the swirl of the roof.
On the exhaust bowl, I used a 1 3/8" Ball end mill and then open the ex to 1.47 @ 60°. In retrospect, a 1 5/16 ball end mill would have been a better choice, I think, as the walls of the port may be on the thin side. I'm going to try to get a sonic test done on these bowls and see whats left.
On the inlet side of the intake, the plan for it, is to machine the pinch point, from .910, to at least .980. The angle of the port after the pinch, is 28° so, I will cut the pinch @ 14° and blend both sides, to as much of a radius, as I can.
The plan for the exhaust exit, is to match the bowl radius with a 1 1/4" ball mill, moving the roof of the port up about 1/16". I think I can miss the SSR that way and I'll open the sides of the port a little, too.
At the moment, I can't find anyone with a flow bench, in my area, to do any testing, after I'm done. There is a guy that builds Sprint Car engines that has one but, I'm told that he doesn't let anyone test on it. If I can't find another, I'll talk to him and see if I can get him to make a exception.
I'm encouraging all that do porting to weigh in on this, I'd like to hear opinions, good or bad.
This is my first attempt at porting, other than matching ports and smoothing obstructions.
I have this old set of C6 heads that I got for free, about 10 years ago. They had screw in studs and a descent set of springs and retainers. Someone had done some grinding on the exhaust ports but not the intake. BTW, when I'm done, I won't use any of that stuff.
It will have LS, 8mm valves, cut down intakes, to 1,900 and the std 1.570 ex. Both with LS guilds installed.
So, with no money to loose, I decided I'd try my hand at re-machining the ports. What you see in the pictures, is a fixture I made to accurately hold the heads, using the guilds and the core plug holes, for height and angle plates (that's what also holds the spuds, in the core holes). BTW, those core holes are exactly the same height on both end of both heads. I think they may have been used in the tooling of the heads when they machine them at the factory. I measure those on my surface plate, as well as the guild C/C spacing. The guilds are exactly 1.82 C/C. As you can see the casting is very close, port to port, so there is almost no core shift, in these. The depth for each operation, is set the same for all cuts. I was impressed at the repeatabilty of each operation.
First I went though with a 60° cutter, opening the throat to 1.83 on all intakes, then I took a 1 1/2" ball end mill and took it to a depth that I felt comfortable with and took out most of the guild, it leaves a very nice look at the built in swirl pattern in these heads. Before I finish the intake bowl, I have to make a 75° cutter, to blend the 60° to never the bottom of the bowl. then blend it all together. From Carnuts thread, I know to be careful with the SSR and I won't try to lay it back, just make the biggest radius I can. The length of the 1/2" LS guild, that protrudes into the port, will be shaped to match the swirl of the roof.
On the exhaust bowl, I used a 1 3/8" Ball end mill and then open the ex to 1.47 @ 60°. In retrospect, a 1 5/16 ball end mill would have been a better choice, I think, as the walls of the port may be on the thin side. I'm going to try to get a sonic test done on these bowls and see whats left.
On the inlet side of the intake, the plan for it, is to machine the pinch point, from .910, to at least .980. The angle of the port after the pinch, is 28° so, I will cut the pinch @ 14° and blend both sides, to as much of a radius, as I can.
The plan for the exhaust exit, is to match the bowl radius with a 1 1/4" ball mill, moving the roof of the port up about 1/16". I think I can miss the SSR that way and I'll open the sides of the port a little, too.
At the moment, I can't find anyone with a flow bench, in my area, to do any testing, after I'm done. There is a guy that builds Sprint Car engines that has one but, I'm told that he doesn't let anyone test on it. If I can't find another, I'll talk to him and see if I can get him to make a exception.
I'm encouraging all that do porting to weigh in on this, I'd like to hear opinions, good or bad.