Frequently Asked Questions

Head Porting

Q - I am certainly tempted to send you the head, because I know you will do it right...but I am also very tempted to look into porting the head myself. I know what you are going to say: DON'T DO IT! I have a very serious desire to learn more about head porting though (I once ported a Briggs & Stratton go-cart motor successfully), and I have confidence that I could do it with the right information. I have read several in-depth articles, and a fellow mechanic ported his own and gained noticeable power. I suppose asking your advice on what areas need the most attention is a little like asking a Texan for his secret BBQ recipe, but I'll ask anyway! Would you be willing to make suggestions so that I can have the pleasure of learning and the pride of accomplishing it myself? I am adult enough to realize that I need to experiment on a bad head first, and I know that there is still the reality that I might screw it up...let me know what you think.
A -
Some heads are comparatively easy to do some basic porting on as what needs to be done is pretty obvious.
Volvo B18/B20 heads are hard to port as what seems obvious is actually the wrong thingg to do.
The only way you can find this out is to actually do some porting and then check the result on a flow bench.
So I suggest that you do it this way. Take a scrap head, exactly like the one you are going to use, with similar core shifts, and have the flow checked. Then port it like you think will work and then have it checked again to see if you were right. You are probably better off doing it one port at a time so you have more chances to get it right. If you do a port that works, then try to do the same thing on the next one. Once you have been able to duplicate it, then do the same things to the head that you are going to use.
Above is the best suggestion I can give you on how to do it.
If you were standing here next to me and we were looking at heads sitting on the bench in front of us I would tell you the same thing. You simply have to develop an eye and a feel for what needs to be done and how one port is different from another.Part of this is due to the common core shifts in the head, so where that one port needs more taken off on the left, another needs more taken off on the right, or the front or the back, etc. So I would actually have to see and feel your head in order to tell you where material needs to be removed.
Another problem is that all parts of the port have to work together. You can improve the flow at one point in the port, but if that is not matched by an improvement at other points, the improved flow can cause the air flow to separate from the port wall, start tumbling and create turbulence. On the intake ports this is typical and is the reason that it really needs to be done with regular flow bench checking. Very small changes in the port shape, particularly on the inside radius make all the difference and some shapes that don't look like they will work, in fact do.
If you don't have at least one head to practice on,  have no access to a flow bench, and can't afford to put the engine together and find out that the head leaks water, then don't do it.
BTW, when I do a head, only a small portion of the time goes into the actual porting. The rest of it goes into installing hardened exhaust seats; milling the combustion chambers to unshroud the valves; cutting the angles on the valves; cutting seats in the head; removing and installing valve guides; reaming the guides to the proper size for each valve stem; removing the soft plugs, removing checking and reinstalling the brass coolant tube that runs the length of the head; reinstalling the soft plugs; vacuum checking the ports to make sure that there is a good valve to seat seal; flow testing the ports to make sure that they flow up to spec for the specific head type; measuring the size of the combustion chamber; calculating the size of the combustion chamber that will give the desired compression ratio; milling the head to produce the desired combustion chamber size for the desired compression ratio; and a few other things that I have left out.
Q  - There's a local Formula Ford guru here at Infineon that does headwork. Can I have him follow his own experience to head port a b20 F head?
A  -  He might have enough experience and take enough time to do a good job, but almost all of the heads I have seen done by people who do headwork, but do not have extensive experience in doing Volvo B18/B20 headwork, have been less than satisfactory.  You need to do at least several of the same head in order to work out what techniques work best on these heads, and after that its a question of degrees - how much is an improvement without going too far.  Its a process that usually requires several "test" or "scrap" heads to experiment on before you can do one for a customer.  Then you need to test the result in the "real world" as high flow numbers do not always result in commensurate power increases.  The head also has to match the cam and other specs of the motor its going to be used with.
Its also a process made a lot more difficult by the casting core shifts in these heads.
Each head is actually a little different with combinations of up/down, right/left, and front/back shifts, so the ports are not equal to start with. One thing you have to be able to be able to do is differentiate a good head core from a poor one just by looking at it.