Porting, Using a Mill

[frnkeore]

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.

[mag2555]

The fact is the area's/ locations within each Intake or Exh port that are the main restriction points to higher levels of flow can not be got at with a mill.

[mag2555]

The fact is the area's/ locations within each Intake or Exh port that are the main restriction points to greatly increased levels of flow can not be got at with a mill.

There are specific geometries that go with reworking and enlargeding any port when digging for greater levels of airflow, and maybe just as important not loosing levels of airflow the given port has now, especially when stepping up to bigger valves!

It's good you concider this a Mule head to learn on, who near by you has a flow bench to qualify your before and after flow numbers?

[PRH]

I would consider that to be “pre-porting” machining.

Now the hard part starts.

[mag2555]

That's a good way to phrase that!
It's like greasing the pan before pouring the batter in I guess!

[frnkeore]

Thank you for the input.

I feel quite confident, that I will be able to finish the exhaust side, using a ball end mill and long 7/16 end mills for the corners, then finish with just a little blending. And I'll be happy with 160 cfm.

On the intake side, I'll be happy with 200-210 cfm. That will meet my HP goal, for this build. Pipe Max, says I can make 440 to 460+ HP with 210 cfm on a 306 engine. For the intake, I have both a Vic Jr and a 300-275, Holley Tunnel Ram. I'd be happy with 425 HP with the Vic Jr. The exhaust side is a Schoefeild 1 3/4" sprint car header. I'm making different tops for the Holley, 2 and 4 (all mounted sideways), 4412's both centered on the ports.

280 CFM aluminum heads, will go on this engine after the dyno runs and these heads (if they survive) and these, will go on a more streetable 332 CI build, with well made, 1 5/8" short headers, that fit a Fox body. With the Vic Jr or, a good 180 intake.

If I can't find a flow bench, the dyno, will be my only gauge.

[PRH]

Without testing it’s all speculation.......but, IMO......

I feel like what has been done so far wouldn’t do much at all for building additional
HP....... if...... that’s all that were getting done. It could easily be a step backwards as well.

Almost certainly, if one were starting with a stock head, with the stock bowl and valve job, 7-10mins with a burr(by someone who knows what to do) would produce more effective results.

It’s going to require a fair amount of porting before the work done on the mill really starts to pay off.

[Walter R. Malik]

I would consider that to be “pre-porting” machining.

Now the hard part starts.

Yep ... I use a mill for getting the pushrod wall straight at the thickness I want.

[frnkeore]

Randy, I don't want to sleeve the push rod holes but, how wide can you get the pinch point, w/o sleeving?

[Joe-71]

You are extremely lucky you haven't already hit the water jackets in several places. Those intakes bowls have to be paper thin. Joe-71

[justahoby]

I would consider that to be “pre-porting” machining.

Now the hard part starts.

Yep ... I use a mill for getting the pushrod wall straight at the thickness I want.

I agree. Not a bad thing to do. But the beginning of the beginning. I'm getting older and lazy, so anything to help.
I have some I do that and hours of.bowl work and top of the port and some short turn smoothing for daily driver stuff. I done my share of head porting all out. Guess I'm lazy because I gave up the idea of racing. 30 0r 40+ hours on heads dust and shit. I think I will save for cnc heads for my use


I

[frnkeore]

You are extremely lucky you haven't already hit the water jackets in several places. Those intakes bowls have to be paper thin. Joe-71

As I said, there doesn't seem to be any core shift on these heads. I studied all of Carnuts section pictures and a few others I found online and it seemed doable. I'm comfortable with the intake bowl but, on the exhaust, I got a little nervous when the end mill started biting into the exhaust, below the seat area but, it was already to late to rectify and I didn't open the water jacket so, I took it to the depth I wanted. then did the rest, to see it it would break threw. The heads were free, so I had nothing to loose. I have another set of 302, D0 heads that I will do this to but, I'll use a 1 5/16 ball end mill on those.

As you may know, I've had this idea of using end mills for opening heads. It first came about with my thoughts on running a ball end mill, down the exhaust port to the guild area and evolved from that.

[mag2555]

My concern for where the port walls may now be thin would be the the rear wall of the Exh bowl right behind the valve guide.

[Fatman]

Could you feed the end mill into the ex bowl on an angle so that it does not take as much out of the back of the bowl? That would mean that it would take more out of the short turn as well.

[Walter R. Malik]

Randy, I don't want to sleeve the push rod holes but, how wide can you get the pinch point, w/o sleeving?

Depends upon the material to me ... others may disagree but, for me cast iron is .050" and aluminum is .075".

I sometimes use the mill with a large ball nose cutter which matches the back wall of the bowl to shorten the valve guides some.