In the thread 'Cam choises' from Yellowbricktoad, it is said: I don't recommend that people do their own porting at home, although the exhaust ports benefit greatly when it's done right. There's too much potential for error.

First: I do not know a hack of a lot about porting.
Second: I opened this thread since I think there are a lot of people here who would like to do their own basic porting work for different reasons. However, it's pretty easy to ruin a head by grinding away the wrong spots. But there must be some basic things you can do yourself to just make that daily driver go a wee bit faster. Well then, maybe this is a good time for a 'basic porting FAQ'.

I think there is quite a bit of -sometimes hidden- knowlegde on how to improve the heads of a B18/20, so I hope all the people who have done some porting to their own heads will hop in this thread and post their opinions. Also, perhaps if someone has got pictures of other heads that are worked on, please post. Post and tell all you have.

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My 2 cents to start with:

-First of all, allways use the thinnest head gasket available to improve quench. Period.

-The intakes on the B18/20 seem to be in good overall shape. Also, intakes are more critical in shape then exhaust ports imo, so I'd say, when doing basic porting, maybe grind the nasty casting flaws (if any), other then that just leave them.
Changing the shape might totaly disturb flow. Enlarging them will decrease flow velocity which is not good for low end performance. For the same reason, dont use a injection head (large intake ports) in combo with a (small) carb: flow in carb and manifold will be good, but will decrease once it enters the port. Basically you'd want it the other way around: increasing velocity towards the valve.

-Most exhaust ports are a bit narrow just behind the valve seat. Thats where you can grind some. On the short side radius grind till there is nothing sticking out in the port beyond the valve seat, making sure the radius is very nice and smooth. Basically do the same on the sides, and also to the opposite side. Just a little bit in the top, so that the wall will allready steer the flow outwards instead of just towards the ceiling of the port (this is not done on the head below). Also, grinding the area around the valve guide is good, but allways leave so of the casting surround the guide, else it will get too hot and bind on the valve stem. Next you can match the port shape top the manifold by putting the gasket on and taking out the right spots. Make this transition smooth, so start at about an inch from the outside of the port. Be carefull not to grind away too much. Better to leave the port a bit smaller then the manifold then the other way around.

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This is just the way I think you might do some porting, maybe its right, maybe its completely wrong. Tell me. Tell us. What is wrong? What is right? We all want to know.

Here are two pics.
Cheers, Ben

A stock E-head:


A ported (start of) F-head:


--
P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

I don't recommend that people do their own porting at home, although the exhaust ports benefit greatly when it's done right. There's too much potential for error.

I don't know who said that, but it is very true.



What you have done here looks very wrong to me. I remove nil from there where you appear to have removed a heap.

Hi Paul, it was Phil who said that, and I too, agree with him. I started this thread exactly because of this: since its easy to screw up.

Tell us why the porting in that pic is wrong. It's not my head, and I didn't do the porting btw, I just used a pic from the turbobricks forum. I would not do it this way either which is what I said in the first post: Grind just a little bit in the top, so that the wall will allready steer the flow outwards instead of just towards the ceiling of the port (this is not done on the head below)

But please tell us what is beneficial and what is not, so we can learn.

cheers
--
P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Ben,
Most people reading this may think I am saying not to port your own heads because I want the business. Not so. I have more head porting orders than I can keep up with and could very nicely limit my head porting to doing heads for the engines we are putting together. And I definitely want to eliminate the business of fixing heads that others have screwed up. Usually takes me more time to "fix" one of these than to do a head from scratch. Right now about 30% of the heads I am working on are in this category, and I keep swearing I will not do another. Then someone sends me a head to test that they ported, or had ported by someone locally. I test it, find problems, and they plead with me to fix it.

So basic advice is: If you do not have a flow bench and access to a dyno to check your results, don't port the head. Also do not take it to anyone to have ported who cannot show you the flow improvements on a flow bench and dyno results of other B18/B20 heads he has ported.

The key problem with giving simple advice is that its not a simple matter.
There are actually 8 different ports in one of these heads - lefts, rights, insides, outsides. Further, each head is cast a little differently due to core shifts in the casting and the fact that a head actually consists of two sections that are not always joined the same. Due to the casting shifts the machining at the valve and intake manifold face are not in the same relation to the port on each head. You don't see this until you have about a half dozen heads sitting in front of you and examine them carefully. So, in essence, a lot of what has to be done is correcting casting differences to try and bring that port up to an optimum standard. The above is a long way of explaining that you can't do the same thing on each port. Work that will improve one, will hurt another.

Any changes that you make have to work together. Improving one area of a port without making an equal change in another can cause the flow to become turbulent, separate from the port walls, with the result that the flow is reduced. This often happens with doing anything to the intake, including smoothing out the flashing. One reason that you need a flow bench to check your work.

For a street engine, don't bother trying to match the port to the intake/exhaust gasket. Its a waste of time and will only hurt things. Just be sure that the exhaust is smaller than the manifold its flowing into and that the intake port is larger than the manifold that is flowing into it.

Can't really tell much from the photo. But the real problem is that the valve seat has not been done. The area from the seat to the area of the port below it, the bowl, is critical. So without a seat its hard to comment.

Quick advice on the exhaust is to do a three angle valve seat (30,45,60) and blend it into an area just below the seat that is approx. 1.150" in diameter. For best flow the actual 45 deg. seat should be approx. .050" wide. Back cut the valve at a 30 deg. angle. Do not spend time rounding off the inside radius as it is easy to hurt the flow by doing this. Do this work at the same time as hardened seats are being installed.

Quick advice on the intake is to leave it alone. Use an injected head, as they flow 10 - 15% better than the carbed heads, depending on the exact casting.
And use one that does not have large core shifts to begin with.

John
V-performance.com

Matching the exhaust port to the gasket...? And then smoothing it back a bit so it's not an all of a sudden increase in port diameter. Kinda like it is when it goes into the exhaust manifold anyway... Good idea or pointless without further work?
--
Kyle - VP of OVT Membership - www.OVTuners.org Portland/Corvallis, OR - 1968 142 - current setup: 71b20b SUs, m40, bigger list available upon request... ;)

Perhaps I did not explain it very well. You want a nice transmission between exhaust port and manifold. Large bumps there will cause turbulence. Since it is hard to check wether they actually match (the port vs manifold) when it's bolted on, you use the gasket. The gasket just about allways corresponds very nicely with the manifold. That way you can just put the gasket on the head and instantly see where large misallignments are.
I also tried to say that if youre not sure whether they match or not, just leave it. It's better to have a transition form small port to a larger manifold, then the other way around.

--
P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Well, what I was doing was just asking another question about doing DIY porting for the experts to answer. Of course you want a nice transistion. Stock there's this rectangle shaped port that just all of a sudden leaves the head and has lots of room to expand when it enters the stock manfold... Actually, you know what? I'm just thinking of headers that have a round port that are attached to the head. the stock exhaust manifolds are also rectangles aren't they... >idiot< :-p Never mind... But then yeah, when you put on a header you'd want to open it up a bit to match the gasket wouldn't you?

And you know what? I just went out and took a look at the exhaust manifold that I had been using on my last engine, and there's evidence of the EXHAUSTMANIFOLD's ports being too small. As in the head port's opening was larger than the opening on the exhaust manifold. The opposite of what would be ok. :-\ Who know's what's going on right now in my motor. I was planning on swapping what's on there right now with the one I just looked at though. But now I'm on a stock B head AFAIK, instead of what could be a modified F head, so we'll see where I'm at when I start taking that stuff apart again.
--
Kyle - VP of OVT Membership - www.OVTuners.org Portland/Corvallis, OR - 1968 142 - current setup: 71b20b SUs, m40, bigger list available upon request... ;)

I race Remote Control Cars, which use a single cylinder two stroke engine that I ported about a year back. All I did was take a dremel to the ports (the cylinder was made of brass with chrome inside) and smooth out the corners. Got a bit more power but the motor also got tempermental unless it was tuned just right. I'm not sure how this will compare to porting a cast iron head. Is it the samw concept with real cars?

I've been reading all the recent talk about head porting. Can someone also give a little information on polishing?
I am assuming once all of the rough grinding is done, everything gets smoothed out with finer grits to make the surfaces smooth(polished). I am also assuming that the intake manifold can also be polished???

In my opinion: polish the exhaust so carbon is less prone to stick to it, but dont polish the intake. Just leave a 'semi-rough' finnish. Some say this is good so "fuel doesn't fall out off suspension" but imo, thats nonsense. The reason why I leave it semi rough is the fact that it creates a small turbulent boundary layer sticking to the walls, leaving a larger laminair flow in the middle of the port. You allways get turbulence/eddies on the walls of the port which will disturb flow. If you can make those eddies smaller there will be less disturbance. When you're a race expert, and know *exactly* how the flow in the port flows, its different since you then might be able to make a very good port shape where there is hardly any turbulance in the first place. In those cases polishing will be good. In the DIY porting, leave a semi rough surface.

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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Polishing the exhaust port excessively;ie "mirror finish" seems to be somewhat useless since the carbon buildup in the port will negate the finish in a hurry. My intention is to work the exhaust side smooth then leave it. I remember reading a porting article in either Hot Rod, Pop. hot rodding, or Car Craft [yah I know they hate imports but sometimes they have pertinent info & I've been a car mag slut since high school even though I HATE Camaros] & it said that it's more imp. to work on the short radius bend because that's where the slow air is. I'm looking for the article in my "archives"[pile of car mags] & will see if I can give us any more insights. It would be nice to see one of JP's heads to give us po'boys something to shoot for but I don't want to take anything away from what he's done & is doing for our old Volvos. I think he's doing a great thing! I'll get some pics when I'm done with my head but that may take awhile, plus I'm a complete Luddite as far as comp. are concerned [this thing is a 386!]

Mike M.

Wide open til you see God.................then brake!