c460 vs. a460 .......

So here's the question: How much of the C460's superiority over the A460 design comes from the port design and how much comes from the valve placement in the chamber?

DaveMcLain wrote:So here's the question: How much of the C460's superiority over the A460 design comes from the port design and how much comes from the valve placement in the chamber?

Dave,

The superiority of the C-460 over the A-460 comes from the following;

1. They raised the intake port even higher. An old quote from Lem was; "He who raises the intake port the highest, wins."

2. They reduced the incline angle of the valve from 13.5* to 8*, in other words stood the valve up.

3. The A-460 stuff had 4* of side cant and the C-460 has 0* side cant. A benefit from this is that a properly designed C-460 piston will always be lighter than a "equal" properly designed A-460 piston. The valve reliefs do not have to be as deep, therefore the crown of the piston does not have to be as thick. In addition, the top ring can be higher on a C-460 piston than an A-460 piston. Furthermore, you are much less likely to have the burn through problem, (where the intake valve relief of an A-460 piston burns through to the backside of the top ring land) on a C-460 piston.

4. The nominal C-460 chamber is shallower and smaller than an nominal A-460 chamber. However, new modern A-460 chambers are an improvement over the older style A-460 chambers.

5. To answer your question as to how much comes from the port design, verses how much from valve placement, it's tough to say, but I would lean towards the port design being mostly responsible.

Hope this helps,
Charlie

Those things are all true about the C head and undoubtedly improvements over the A design but I've been thinking about how the lack of side cant in the valves could be a mixed blessing. This is from thinking about how the C head originally comes from the Yates design which was designed for about a 355 cubic inch small block engine running between about a 4 inch to a 4.155 bore diameter. With that thought in mind it seems as though the Yates design is really laid out with a large bore relative to the displacement in mind. The big block engines tend to have a relatively smaller bore when compared to the displacement of the engine. Is this the approach that's used in the Thor and other heads? Aren't they based on the C design but with a side cant?

Interesting stuff.

Dave,

Yes, I see where you're coming from when you say mixed blessing.

1. The Thor heads are like a bigger C-460 head, but with side cant in both valves of 3.5*.

2. The Profiler #205 heads are again like an improved C-460 head, with bigger as cast ports and big radius rounded corners, but they do not have side cant. Their camber is even shallower, with a nominal 60 cc volume.

3. Darin Morgan, the designer of the new Ford NHRA Pro Stock heads will be one of our guest speakers at the Winter Tech Seminar on Jan 16. I want you to save this question for him, however, I "think" with the latest generation of heads, that the designers are striving to put the valve pierce points on the cylinder diameter, not a chord, because that gives them the most possible room or side to side distance for the valves. I also know that they are shrinking the exhaust valve size in order to increase the intake valve size. I see no problem there, except with engines that are going to use a heavy dose of nitrous, and/or are supercharged.

Hope this helps,
Charlie

Cant is good .

Lem Evans wrote:Cant is good .

the grand pooba has spoken....