[gtofreek]

Here ya go. Sorry it's not a Pontiac head. I have thousands of pics and this is what I could find for you right now. This is just one type of bowl hog. There are several types. This one is adjustable by sliding the cutter up or down. It is 70°

[tempest1964]

How does that cut? Seems like it would want to chatter. Is the set-up and cutter pretty rigid? What kind of speed and feed? Just curious. I have a little machining background but nothing in this field.

[gtofreek]

We use carbide pilots which help a lot with stability. I also cryo treated the cutters, cutter bodies, and pilots, and that also helped with chatter. if you go slow, they usually don't have much problem with it. Biggest thing is since it's not cutting all the way around, you have to be careful on your feed rate.

[tempest1964]

Good stuff Paul. Thanks

[steve25]

Here's how I start off for a Head that will flow into the 270 cfm Intake range.
The cutter use was a 1.785", but for numbers into the high 280 cfm range a 1.850" cutter is used.
As can be seen I drop down into bowl untill the cutter stops removing material from the short turn and then I continue on with Hand porting.

As you can see this Head as very little core shift which is what is needed when your working with Throat sizes like this.

The second shot is the cutter down in port that is fully done and flowing 278 cfm.

My last shot is that 1.785" cutter way down in bowl of 290 cfm #13 casting and you can see the daylight around the cutter

[beertracker]

Take a look at the photo between the 4 white paint dots. The arrows show the area I am concerned with. I am cutting back the chamber toward the gasket to reduce valve shrouding.

Should I make the cut so it touches the gasket or just enough to take the curl lip out and leave some metal between the chamber edge the gasket?

I already made shrouding cuts on this head and am re-checking it before moving on. I traced the combustion chamber gasket opening on the head. You can't see the line because of the gasket.

Thanks, bt

[steve25]

Don't even bother with the Exh side unshrouding, but roll over that or any sharp edge on the chamber lip.

Do the unshrouding on the Intake and do all the chamber lip rolling over so that the roll over stops just before the fire ring on the head gasket.

Also be sure to just very lightly break the sharp edge of the eyebrows in the chamber, along with the machine edges around the spark plug, do this rework with the valves in place in case you slip!

This type of unshrouding, blending / polish and roll over work will add 2 CCs to your chamber volume.

[beertracker]

Which cutter do you use when elongating the push rod holes for 1.65 rockers?
Cutter style, width. shank length?

My double cut 3/8 acorn and 1/2 reverse cone didn't work well. I am using 6" long shanks.

The end push rod holes on 6X heads are recessed below the other push rod holes. Should I elongate the end push rod holes also?


bt

[Will]

I use a small 1/4" oval for the pushrod holes. You only need to elongate about the top 1/3 of the hole.

[68azbird]

With 1.65 HS rockers i had to slot the holes over .250" or more to have adequate clearance.

[steve25]

The amount and depth of the slotting will depend on if and how much the Heads have been milled, and of course your push rod lenght and diameter being used.

Sometimes with bigger diameter Rods and milled Heads even the bottom of the hole on the lifter valley side needs some tweaking!

[beertracker]

Originally Posted by steve25

The amount and depth of the slotting will depend on if and how much the Heads have been milled, and of course your push rod lenght and diameter being used. Sometimes with bigger diameter Rods and milled Heads even the bottom of the hole on the lifter valley side needs some tweaking!

Planning on using stock 5/16" push rods. No milling of head but I plan to zero deck the block so .023" will be cut off. Push rod length may have to change because of this.
What about the two end push rod holes on 6X heads that are recessed 1.5" below the other push rod holes. Should I elongate the end push rod holes also?

Maybe a 7/16" straight wall cutter with 2 or 3" shank would work better elongating the push rod holes?

bt

[steve25]

Then all you should need is a 1/8" more at the top and then tapering down to the stock hole size at 2" in.

But always double check !