Head Porting Basics
NOTE: Proceed at your own risk, as the author of this article will take no responsibility for any damaging effects caused by following (or not following) the instructions herein. This article written by Ashentep, please do not copy without proper credit.
Tools/Supplies needed:
Set of heads (duh) (junk heads if its your
first time)
Valve spring compressor
Die grinder (~20k rpm), electric drill, or maybe even a Dremel tool
Carbide burrs (not required, but preferred) or Grinding stones
Emery rolls (AKA: sanding rolls) available from Summit, and many part stores
Brake cleaner
Brass and/or Stainless steel brushes
Disassembly:
I'm going to keep this section short and sweet. After all, this is a porting basics guide, moreso, than a how to disassemble/reassemble heads guide.
1. Use the valve spring compressor according to directions to compress the spring far enough to remove the valve locks. If you are using the style where you pry the spring by hand, a hammer may be useful for freeing "locked" locks.
2. Carefully release the pressure on the valve spring. Remove the retainer, valve spring, and valve.
3. Grab the valve seal with a pair of pliers and pull it off the top of the valve guide.
4. Repeat for every valve on the head.
Inspection:
Before jumping into porting, you're going to have to inspect the heads to see exactly what needs to be done. Do the exhaust ports have a bump for air injection/EGR? Do the valve bowls (we'll get to definitions in a second) have sharp edges? Is the short side radius smooth? Is the valve guide dominating the port? What other things are limiting flow?
I can't go over everything (nor do I know anywhere near everything) you will see or need to do when porting a set of heads. I will be working with a set of E7TE heads, and will use what needs to be done to them as an example.
Definitions:
Short side radius: The radius of the slope from the port to the valve bowl opening
Valve guide: This is the raised section in the port that the valve goes into. It usually is very large.
Valve bowls: This is the section under the head of the valve that resembles a bowl. It has three walls (inboard, outboard, back) and a roof.
Port: This is the section that air flows into from the intake manifold to the valve bowl, or on the exhaust side, from the valve bowl to the exhaust header/manifold.
1. Start looking at the valve bowl. The first thing you'll probably notice is the valve guide, on the roof of the valve bowl. It has a hole, which the valve stem goes through, and serves as a guide for the valve, keeping the valve's motion linear. Now, the factory makes this guide very large, so it can be trimmed down, but try VERY hard to keep your tools out of the middle, as well ask keeping the height of the valve guide the same. We can trim the sides of this down, but don't go too thin.
2. The second thing you will probably notice is that the walls of the valve bowl will have ridges and sharp lines in them from when the seat was cut in. These need to be smoothed, and often the entire "throat" of the valve bowl opened up to a more constant diameter. Now, the general rule is for the "throat" of the bowl to be 90% of the diameter of the head of the valve. Get a rough estimate of what this would be (.9 x valve diameter) and try and have that as your goal. Be careful when removing material from the walls. There are water jackets in the head that carry heat away from this area, and if you break through, then the head is a big paper weight or door stopper!
3. The short side radius is usually more of a sharp corner than smooth radius. We want this smooth, but don't too much material off here. This will either make or break your port. The short side radius is one of the most essential parts of the port. You want a smooth, flowing radius, but don't make it too large. You want the port (on the intake side at least) to ramp up a bit from the entrance, then make a somewhat sharp, but smooth turn straight down to the valve head. Its best to use a sanding roll here and take your time, especially your first few times.
4. Lastly, the port. Inspect the port for any sharp turns that can be smoothed. Also, at the very opening of the port, there are usually humps on both sides for the pushrods. These can *usually* be ground flush with the walls, but I can't assure you that every head will allow this without breaking through. You should be more or less able to look at the head and tell the position of the pushrods compared to the buldges.
5. Gasket matching: simply put, forget what you've heard. 9 out of 10 times, the factory knows where to position the port for the best flow. Moving the port, or widening the entrance is usually a waste of time, and sometimes can even impede flow. The best thing to do, is line up the gasket, see where the port is in relation to it, then if say the roof of the port is very close to the gasket, go ahead and match it up. If the floor is say 1/8" or more away, forget matching it up. Its probably that way for a reason. Bigger is not better in most cases.
Examples: This set of examples is what I did to a set of E7TE heads (stock '87-95 5.0 LX/GT heads). Use these as a guide only.
On the right is the intake, left is the exhaust. There's not a lot I can tell you that I haven't already. Excuse the bad picture. The shiney metal (after clean up and porting) makes for a lot of relections.
Take particular note of the smoothed walls and valve guides. I try and trim the sides and back of the valve guide to allow flow to come around the side of the guide and to the back. Compare these with the pictures above. I was unable to get a good picture of the short side radius or ports of either the exhaust or intake.
Summary:
Well, I told you this was goign to be a quick and very BASIC guide. This is more meant to get your curiosity up than anything. I don't suggest reading this and getting out there and porting heads. You should read this as a very basic primer, then go out and research your individual heads, as well as ask any local speed shops what they might suggest you do, and even reading airflow physics. If you know where the air wants to go, then you can do some serious reshaping of the ports and bowls to get the most flow possible from the heads. There are a LOT of rules to porting (such as the 90% throat diameter vs valve diameter) that is not even mentioned in this guide. Now get out there and do some research!