oval port or rectangle port
Thread Starter
CF Beginner
Joined: Nov 2010
Posts: 3
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From: wisconsin
oval port or rectangle port
Hey folks..Im buildin a 1975 454...I'm tryin to determine what heads to use..I just had a well known engine builder tell me that oval port will be the better option for this build.. I'm strokin it to a 496 and shootin for 625hp...Why is oval gonna be better than rectangle.. goes against all i've ever know about heads..? Any input would be great..
CF Monarch
Joined: Jul 2007
Posts: 5,891
Likes: 29
From: Princeton, NC, USA
Looks to me like the oval will actually provide more airflow even when it has less volume than the rectangular.
From my experience with Heating & A/C ducts, I can give you a little more scientific answer.
Air will naturally flow in an elliptical (rounded) shape regardless of the shape of the duct ("port" when applied to engines). In a rectangular duct, turbulence caused in the corners of the rectangular duct can slow the overall velocity of the air. This is called a static resistance and reduces the static pressure. We prefer round duct to rectangular duct because of that so we can handle more air with a physically smaller duct and maintain a strong flow of air over greater distance. It also allows us make the air change direction without losing velocity. Same goes for the heads.
Cylinder heads have a terminal velocity, if you will, or a maximum rate at which fluid (air) can travel through them on the intake cycle. A round port will have much less resistance to flow and can support airflow at a greater rate than will rectangular port.
From my experience with Heating & A/C ducts, I can give you a little more scientific answer.
Air will naturally flow in an elliptical (rounded) shape regardless of the shape of the duct ("port" when applied to engines). In a rectangular duct, turbulence caused in the corners of the rectangular duct can slow the overall velocity of the air. This is called a static resistance and reduces the static pressure. We prefer round duct to rectangular duct because of that so we can handle more air with a physically smaller duct and maintain a strong flow of air over greater distance. It also allows us make the air change direction without losing velocity. Same goes for the heads.
Cylinder heads have a terminal velocity, if you will, or a maximum rate at which fluid (air) can travel through them on the intake cycle. A round port will have much less resistance to flow and can support airflow at a greater rate than will rectangular port.
Thread Starter
CF Beginner
Joined: Nov 2010
Posts: 3
Likes: 0
From: wisconsin
Yeah I'm finding out that oval does have more flow until the lift gets to .650 then rectangle port has better flow..I guess oval port has come a long way. Definetly a good porting job is needed for the oval to surpass rectangle's performance..I would think cnc or done by someone with some good experience doin it manually...
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