Cylinder Head Port Design - CHP How It Works

Part 2 Of Our Cylinder Head Roundtable. Our All-Star Cast Of Experts Chime In On The Most Intriguing Aspects Of Cylinder Head Port Design.

Stephen Kim May 4, 2010 0 Comment(s)
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Tony Mamo: "The ideal shape for a combustion chamber is a design that best complements the port design and port bias of both the intake and exhaust ports. This may take quite some time to figure out if you're a perfectionist and are constantly striving for more. Unfortunately, there is no blanket statement to be made concerning chamber design and shape, but most of the chamber designs I tend to arrive at all seem to have a figure eight design to them with purposely shaped approaches to both the intake and exhaust valve. I think that combustion chamber development often gets overlooked and it's actually an area I spend quite a bit of time working on, as I view it as an extension of the intake port and as the entrance to the exhaust. Both are very critical to flow and need slightly different shapes to optimize their respective jobs. You would be surprised how much airflow-and ultimately power-can be found in getting the chamber nailed just right. It can really help improve the flow curve of a head, which ultimately can separate a good head from a great head come dyno time. A good chamber design also usually shows itself in needing less ignition lead time for maximum power, and that's another perk. Less ignition advance is usually more reliable over the long haul, especially when using power adders such as boost and nitrous oxide."

Jason Neugent: "Chamber shapes will differ based upon the valve angles, plug location, and the valve seat angles. The combustion chamber needs to be the best compromise to complement these factors to support good airflow as well as proper wet flow. More than any other factor, the shape of the chamber determines how efficiently a motor burns the air/fuel mixture. That being the case, it's imperative to invest just as much effort into the chamber design as the port design."

Bryce Mulvey: "Getting the angles right from the valve seat into the chamber is one of the most important parts of the entire head. If you cut it too flat, you'll get wet flow separation and mess up pressure recovery. You'll also create vortexes that hurt flow as well. Most people go with a 45-, 30-, 15-degree valve job. I prefer a 45- to 35-degree cut right into the bowl so there are no flat areas for the fuel to drop out of suspension. The valve job really is the foundation of airflow since air has to negotiate the turn around the valve as it exits the port. We've seen heads pick up 25-30 hp just by changing the valve job and throat diameter. A common mistake is to undersize the throat diameter, so it should always be sized properly based on valve diameter. Combustion chamber shape is also important, but plug location is very important too. If you have a bad plug location within a good chamber, you will hurt power quite a bit. Likewise, if the plug is positioned too deep inside the head, fuel will huddle around the spark plug hole, which requires more ignition timing and increases pumping losses."

Kevin Feeney: "At RHS, our cylinder head designers believe the combustion chamber shape is probably the second most important part of the cylinder head. The shape of the chamber can greatly affect the spark timing an engine requires, and can cause a lack of fuel in areas of the cylinder, which will make for a real uneven burn in the cylinder. This severely wastes potential power. The chamber shape determines how the fuel is dispersed in the cylinder, and varies depending on the type of valve angle in the cylinder head that you're working with. For example, you would not use the same chamber shape in an 18-degree head as you would in a 23-degree head."


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