oval port or rectangle port
November 16th, 2010, 8:56 PM
#1
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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..
November 16th, 2010, 10:02 PM
#3
CF Monarch
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.
November 17th, 2010, 5:05 AM
#4
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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...
November 20th, 2010, 2:50 PM
#6
CF Pro Member
if aftermarket im pretty sure rectangle port is the way to go, but if dealing with factory heads find oval port heads they were the one used in muscle cars
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