Won't change the velocity but the 320cc port is 'larger' in the eyes of the public.

So, furthermore,
'
say if we raise the 305cc port, thus giving it a straighter and better line of sight to the back of the valve, but doing so we make the port longer. Say it's now a 320cc port.

It picks up some airflow, is much more effecient, and it's 'velocity profile' improves.

Is the 'bigger' head at 320cc passed by for the 305cc head because the 305cc head 'is smaller' and thus have better velocity ?

Example:
How can an LS small block head at 250cc+ absolutley kill a 180cc 23* head on the same size 358cid motor ?

So...sometimes bigger size is just more length.

The intake manifold dictates what the final length is. So, that is used for 'wave length' tuning, not the length of the cyl head port.

Did not know that .

I gotcha, that's why the big chief stuff makes so much power because the ports are so much taller and you have a better path to the valve.

He was there production manager. I'm sure a company of that caliber is going to have there ducks in a row but you never know.

Alex didn't you do a very mild 540 with the 305 head, and get some excellent numbers not to long ago?

I think a lot of times we get caught up in runner size, and tend to use it as the end all decision in using a particular head. Everything must work together. The port size, shape, valve size , valve cut, valve seat cut, chamber design, and so forth.

We might say well a 320cc intake runner works best with a 540ci. But, a 320ish cc GM rectangle port head, would make less power than a 305 AFR, and prob a 357 AFR on that same engine, even though the runner size may not be the textbook size for the combo.

That is how I was thinking until Bob M. tightened me up . Still took a bit to get through this thick skull .lol A lot of parameters figure in to find the best fit for a particular ci engine . I've got a lot to learn . :readinghelp:

Thing is a 315, 335, 357, 385 can all work on a 540 just depends how many rpm you want to spin it. When you go from a GM head to an AFR the valve angle changes that opens up the possibility for a much better port.

Here's the reader's digest version-----If I remember correctly, I was Bob Madara's 1st or 2nd customer when it came to buying AFR heads as he went into business about 10 years ago. I had to rebuild a pair of short deck 565cid engines that I had taken the wrong advice on----very long story. By that time, I was beginning to get kinda "gun shy" about who to trust anymore about cam grinds, heads sizes, port volumes, port velocity, etc, etc, etc. In the business of Hi-Performance offshore boating, there are many voices out there all wanting your money...and it can become very easy to become confused.

I finally found a person I truly believed I could trust in Bob Madara and his business "Marine Kinetics" and Dave Wesseldyk's engine craft building abilities----both extremely intelligent dudes. That was 10 years ago, and we're doing it again now on another different tall deck engine project-----this time, a pair of simple roots superchargers with carburetors.

Anyway, after consulting with Bob, he suggested AFR 315cc, cnc ported heads for the those N/A 565cid engines...he the did cams too---they were runners!

http://www.marinekineticsonline.com/