When someone brings a head to you porting, what would you most prefer they bring you? Raw casting? CNC Ported?

 

Taking a CNC head for any kind of extensive hand porting kind of defeats the purpose. Granted, some improvement might can be made if we're looking for a bit more airflow but take them to someone who doesn't know what they're doing and you could very well end up with a head that flows a few more cfm but makes less power.

The CNC designs are usually patterned after heads that were heavily developed and considered "successes" in whatever application they were originally intended for. Doesn't mean they're "optimal" for your specific combination but the fact still remains that they are more consistent (port to port) than you're likely to find in a hand carving.

Based on my experience, head porters tend to like to work from raw castings as they have their own idea of what they'd like for the port shape. Especially in race heads, where they are cast well under finish size to allow for this. So there are plusses to each approach. Modifying a CNC port is defintely less time consuming than starting from scratch on a raw port... especially one with a lot of material to remove.

-Mindgame

 

I had a feeling...


What about in terms of "as cast", as opposed to "raw casting"?


For instance, suppose I bought a 502 short block from GMPP and wanted to buy a set of AFR 305 "As cast" heads to go on it. I can send it to the porter like that, but I can also buy the same heads in a bare casting.

Either way, it's the same casting, just one is assembled and is bare.

That leaves the entire valvetrain selection to do.

Do most porters have different ideas in terms of valves, springs, etc., making it desirable to bring it bare, or should a person just go ahead and buy the assembled head, to get the price break of buying a complete assembly, instead of individual parts?

 

A "raw casting" may have no machine work done to it at all. Lots of CNC time would be needed just to finish all the flat surfaces, drill holes, macine the guide and seat areas, the chamber, the rocker cover rails, etc. and install guides and seats. An extreme example is the GMPP Pro Stock raw casting which looks more like a chunk of aluminum with "ports" about the size of your thumb, and virtually no combustion chamber cast in.

You can get heads from some manufacturers (AFR comes to mind) with everything machined except the ports, which are "as cast", with only the intake manifold side roughed in about 1/4 inch deep. The head guy then has lots of material to remove where he wants to remove it, and doesn't have to add weld to get the proper port shape. Absolutely discuss this with the porter of your choice.

Either your head guy, or better yet, your engine designer should help choose valves, springs, retainers, etc. to compliment your engine design. Head manufacturers buy all these parts and resell them; they don't make valves, springs, etc.

My $.02

 

Most manufacturers list the extent of work done to the port and combustion chambers. You just have to read the descriptions carefully. "As cast" could mean that the combustion chambers and under-seat area are cnc ported. Could mean that only the combustion chambers are, just depends.

A "raw casting" is something I generally think of as a cylinder head that has NO machinework to combustion chamber or port. They're just like they were when they came out of the core boxes at the foundry... maybe cooler.

But that's not a universal term or anything so who knows. When in doubt... read carefully... call and ask.... talk to someone with experience.... you get the picture.


The valvetrain setup is very specific to the application. So much, that I wouldn't buy a fully assembled cylinder head with all the hardware. I'd want to pick the hardware that would work best with the rest of the combination and I'm sure any professional engine builder feels the same way. Besides, it's a lot easier to verify the quality of the parts if you know exactly where they come from.

Good luck.

-Mindgame

 

Thanks, guys. Your replies have been helpful.

 

Agreed,

Valve length, valve size, weight, material, springs, retianers, locks, studs or shaft mounts etc.... the castings are one part of the deal but the valvetrain really does have to consider the rest of these parts, once you have X part here or there it really limits where you can go with things.

Bret