Understanding port swirl
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Racer
Joined: Mar 1999
Posts: 292
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From: Vienna VA
Understanding port swirl
The head manufactures advertise port flow numbers and port size (affects velocity). I never see any specifications regarding swirl performance.
My understanding is that a good port design for swirl will show up as improved low and mid lift port flow numbers. For comparing aftermarket heads...is there more info required to compare performance potential between heads?
My understanding is that a good port design for swirl will show up as improved low and mid lift port flow numbers. For comparing aftermarket heads...is there more info required to compare performance potential between heads?
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
In David Vizard's books on building SBCs he mentions that stock #113 Vette heads ('88-'91) already have good swirl and that porting should be done so as to not diminish it or, even better, to enhance it.
Further, swirl seems to depend on factors like port bias, chamber design and valve lift. I think that swirl is both complex and difficult to measure, so is not usually even mentioned as a head spec parameter. Yet it is very important in extracting the most from a set of heads.
Further, swirl seems to depend on factors like port bias, chamber design and valve lift. I think that swirl is both complex and difficult to measure, so is not usually even mentioned as a head spec parameter. Yet it is very important in extracting the most from a set of heads.
Burning Brakes
Joined: Aug 2001
Posts: 1,238
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From: walled lake MI
port swirl (and tumble) are difficult to describe with a number, or even several numbers since much of the effectiveness of the swirl has just as much to do with the geometry as well as the speed (linear & rotational) of the mixture.
what makes swirl and tumble even more interesting is how combustion chamber and piston design affect how swirl and tumble changes as the piston compresses the mixture, kinda like a figure skater pulling her arms in to spin faster.
i'm guessing here, but swirl and tumble are only part of the picture. i would also thing spark plug placement relative to the mixture flow would also significantly affect how effective the swirl/tumble performance is.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by Carl90
The head manufactures advertise port flow numbers and port size (affects velocity). I never see any specifications regarding swirl performance.
My understanding is that a good port design for swirl will show up as improved low and mid lift port flow numbers. For comparing aftermarket heads...is there more info required to compare performance potential between heads?
My understanding is that a good port design for swirl will show up as improved low and mid lift port flow numbers. For comparing aftermarket heads...is there more info required to compare performance potential between heads?
Port swirl and combustion chamber swirl, while similar in nature have two different advantages. Swirl (turbulence) in the combustion chamber helps spread the flame front around, resulting an a quicker, (fast burn) more efficient, combustion process. One way to promote swirl in the combustion chamber is to build in the tightest quench area you dare.
RACE ON!!!
Last edited by CFI-EFI; Jan 17, 2005 at 02:59 PM.
