What Porting IS

A common question is, “What is porting?â€￾ So I have drawn up some pictures to show a stock intake port, its problem areas, and a possible approach to a modified head.

The first drawing is just the stock head.



Some of the areas to take special note of are 1. the sharp edge where the combustion chamber meets the block surface. 2. the boss of the valve guide protruding into the port. 3. the lip created by the valve seat insert. and 4. the shrouding of the intake valve by the combustion chamber. The areas are highlighted.






Now - don't laugh at my weak PhotoShop skills - a modified port. I worked on the four areas mentioned above. They are highlighted. You'll notice that there is no attempt to enlarge the port itself. The combustion chamber has been enlarged slightly to unshroud the valve and to grind the sharp lip left after milling - getting rid of the sharp lip is ESSENTIAL or it will create a hot spot.

The bowl work on the seat lip can easily be done by the machinist when doing a three-angle valve job. The valve guide work is easily done with a Dremel and some patience.




Once again, I hope this clears up some of the confusion. There's NOT much that can be done past the bowl area because of the cast-on log manifold.

Thanks Dennis,

I have always wondered, what if a person got to crazy around the valve guide? Could you remove too much in this area that it would weaken it, or that the valve could have bindage during its motion? Or could grinding it up higher gain any flow?

And I had forgot all about the sharp edges caused by milling

When unshrouding the valves, if a larger combustion chamber is desired (turbo application possibly) can you lay the edge back and extend it all the way to the edge of the opening in a head gasket?

-ron

The Ford SIX has a pretty long valve guide and it's unlikely that grinding it away in the bowl area would affect the valve's movement. However, tapering it is probably sufficient.

Yes, you can unshroud all the way to the head gasket line.

I am asking to get this added as a "sticky" so please start a new topic if you have more questions.

Good Luck

hi guys
how do i get pics up of the port jobs ive done i think their the goods ....

ive dethrouded around the guides but with a ridge leadiing up to the guide...
splits the airstream into two,

exhaust ports are more difficult on my ohc, anyone got any sugestions???

Howdy fellas,


We had too much time on our hands one evening and dropped the saw through a damaged Carb'd 300 head. One pic is intake and the other is exaust, but I don't recall anymore. All I know is that they are great bookends



Hope this is mildy useful...

Fabricator

Fabricator":sz1dg0j9 said:

Hope this is mildy useful...

Click to expand...

Sorry, it goes WAY beyond "mildly" useful

i'm pretty sure that'll help a good amount when i drop off my head to get it worked
seriously, thanks for that

One question Dennis. In the write-up you say that you can increase the size of the combustion chamber while you unshroud the valve. Won't changing the physical size of the combustion chamber alter the compression ratio? After the porting is complete would you need to mill the head down to maintain CR?

Thanks
Kris

Yup, unshrouding the valves (and polishing the chamber) lowers the compression.

You could bring the cylinder pressure back up with a flat-top piston, head milling, block milling, or a supercharger. With the supercharger, you won't want much more that an 8:1 compression - depending on the boost.

I would like to Give a little advice for anyone doing port work for the first time. When you start porting the head, pick an area like the exaust bowl area under the seat. It could be the short side radius or the back off the bowl it does not matter, but work this area on all six ports then do another area, again all six ports then move on.

I have seen many first time port jobs and they are usualy pretty good for the first time. The one thing that I almost always see is unbalanced flow. I am sure some of my early port work was the same. Most people seem to work one port to completion at a time and each port recieves a little less or more as you go. Start great and finish tired. One big port and 5 to 7 progressively smaller ports.

If you work one area at a time and finish all six in this area you will be able to duplicate your results more closely. If you get half way thru the port job and decide port work isn't fun anymore it will be balanced better even if it isn't finished.

Good advice, stubby - I'm about to take on my first porting/polishing project, and know I don't have enough time to do all of the combustion chambers, valve areas, exhaust manifold, carb opening, etc. Hot 6 T Falcon's comment about all of the different ways to bring compression back up is why I'm hesitant to take on combustion chamber work. My bottom end is good and not going to come apart for new pistons or decking...

Super long post on all of this about to appear

Some basic porting stuff I've found in my internet quest for info.

http://www.popularhotrodding.com/tech/0610phr_cylinder_head_porting/index.html
http://www.mondellotwister.com/ArtHeadPort.htm

Anyone have copys of the pictures they can repost?