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