I recall seeing an article, including diagrams, on porting 351/400 heads. Does anyone know where I can find this information? I'm getting ready to do a number on a 78 400.

 

Try this. http://www.sa-motorsports.com/diyport.shtm.

 

Thanks. I printed it off and will read it several times to make sure I understant it fully. There is a lot of info there.

 

There are a lot of threads here re porting heads also that you might want to read. Some of the things in that article are misleading. Gasket matching for one is a no-no for most applications.

Remember that SA is in the market of selling abrasive materials so the more grinding you do the more they sell...

 

Undoubtedly true.

 

Why is gasket matching a "no-no"? It seems to me that if the metal is not sandwiching a gasket, then it can go. I opened up my exhaust almost 1/4" by doing that.

 

The articles describe a process that will end up with worse flow characteristics than you started with. Gaskets are never cut the same, they wont lay the same every time, and the manifold will not fit up to the head exactly the same from one use to the other. An allowance for mismatch must be built into the system. Different gasket manufacturers have different dies for cutting the gaskets and they can even vary within a production run. There is slop in the gasket fit also. The gasket must never protrude into the flow path. The flow must always flow from a smaller opening to a larger one. On top of that many intake manifolds "aim" the flow in a certain way to create swirl in the chamber etc. The intakes are sized to provide for port mismatch between parts and gasket tolerances as well as proper flow. About all you should do to the intake is clean up any flash or irregularities. The exhaust is not as much of a problem as the intake with respect to "aiming" but there is a definite flow path thru the port. Whatever you do must be done with careful consideration to prevent a mismatch in the future or flow velocity changes due to volume changes that can be detrimental to overall flow rates. The print "tech" articles oversimplify the problem. There is a lot of information out there. Sorting it out is a problem tho and without experience and instrumentation like a flow bench it is difficult to do the right thing and not get carried away.