Valve Face Shape

I got into a discussion regarding flat faced valves and this is some of the more important tid bits.

located here - http://preludepower.com/forums/showthread.php?p=2422461#post2422461

My reasoning for using a flat/convex valve face on the exhaust side and concave/dished valve face on the intake side is explained by the following:

this is just personal theory. i have nothing backing it.

think about using a air blower with an exit diameter bigger than a dinner plate that is concave. the dish of the plate (valve face), imo, is going to cause a type of air reversion which is working against the point of the exhaust stroke. To escape the burnt up exhaust as fast as possible and to clear the cylinders as best as possible for the intake stroke. Clearing the cylinder the most will make the intake inlet air cleaner for the combustion process where there are more parts of fresh air molecules vs. already burnt molecules which arent going to burn anymore.

Now take that valve and make it flat and you decrease the reversion and increase flow. This is especially beneficial with the correct valve angle grinds performed. Now the other part that i have heard no discussion of, at least in my short research of it, is making a valve face that is actually convex to promote better flow around the valve face while the engine is on the exhaust stroke. makes sense to me, but i have no technical data behind it.

the reason for a dished valve on the intake side is for the low pressure area underneath the valve during the intake stroke.

- Thanks Rocket for the great picture

the dished face increases swirl in this low pressure area and helps promote atomization before the compression stroke. The more you atomization the fuel, the easier it is to burn more efficiently and thus the more power you can extract from the engine given the exhaust can keep up with the intake.

like i said this is all my own theory but one of these days when i make it in this industry and have money to throw away on learning new shit, i would like to test it out.

Then why not have a "domed" exhaust valve? Weight? and the piston possibly smacking the valve when used in close tolerance?

weight is one thing and clearances are another. However, the weight added to a valve that is already lighter than stock will probably just put you back in the realm of having a stock weight valve. You can always build a piston valve relief around the valve but at a tad higher cost and a wait time to cut them about 6x greater than buying them off the shelf. the pistons for my motor will take 4-6 weeks to get made. But mine is a little less involved than having to build a valve relief. Motors such as mine and rosko's run such tight clearances that a hundredth of an inch can determine the difference between right and broken.