by Ron Melville
Any damage that results from using or employing any of the tips outlined below are NOT the responsibility of AIR FLOW DESIGN. Use the tips with caution. You are responsible for any damage or injury that may occur. Use caution at all times!
In this short article, I would like you to remember a few things about airflow. First, air is like electricity in that it will take the path of least resistance, but in order for air to move, there needs to be a pressure differential. OK. Refresh your memory about the four cycles in a four- stoke engine plus cam overlap! If you understand the four cycles and the reasons for cam overlap, this article will be easy to understand.
Cam overlap along with offset intake exhaust valve heights from the combustion chamber side is what helps and can improve the intake cycle, but is often overlooked by engine builders. Why? I guess because they think the piston has not come up to TDC during overlap so the exhaust will go into the intake port. This is true if the intake valve is lower than the exhaust valve in the combustion chamber and the engine is running at a low RPM with lots of cam duration. However, you can change the pressure differential on the exhaust valve side of the combustion chamber if the exhaust valve is lower in relation to the intake valve height from the chamber side. Remember what I said about pressure differential? Now I'm not saying I can stop reverse flow into the intake port, but the problem can be improved to a certain degree with Z-flow.
The lower height of the exhaust valve from the combustion chamber side helps create a low-pressure area. This low-pressure area is what helps most of remaining exhaust go out the exhaust port that in turn creates a vacuum in the intake port that will start pulling the new air fuel mixture into the cylinder. Now think about this. If you reversed the heights of both the valves, you would be sending the air fuel mixture out the exhaust port. I see this problem all the time and I can help you tap in the power of what I call Z-flow. The photo below is just an example and not the exact installed height.
http://www.airflowdesign.com
