Why port volume or cross-sectional area? Can we do better?
07-17-2007, 06:43 PM
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Why port volume or cross-sectional area? Can we do better? I see both measurements as falling short. Cross-sectional area only tells you about a section of the port, and depending on where that's located, it may or may not mean much with respect to flow and velocity.
Volume is even more misleading. It tells you nothing about port shape, velocity, and we all know there are plenty of examples of 200cc ports flowing much better than 230cc ports.
Is there a better way to quantify port characteristics and correlate them to performance usage?
The problem is that defining a 3-d shape in simple terms is an elegant impossibility.
Comparing the ports of a LS to an older style head and the superiority of design is obvious. I'm also looking at a sb Mopar head that flows 290cfm from only 200cc of volume. I like the small-volume, high velocity school of thought, and if I can get the flow with a smaller port, I think that's just bonus.
Perhaps a ratio of volume to flow at different lifts is a better indicator?
Just wondering out loud...
Volume is even more misleading. It tells you nothing about port shape, velocity, and we all know there are plenty of examples of 200cc ports flowing much better than 230cc ports.
Is there a better way to quantify port characteristics and correlate them to performance usage?
The problem is that defining a 3-d shape in simple terms is an elegant impossibility.
Comparing the ports of a LS to an older style head and the superiority of design is obvious. I'm also looking at a sb Mopar head that flows 290cfm from only 200cc of volume. I like the small-volume, high velocity school of thought, and if I can get the flow with a smaller port, I think that's just bonus.
Perhaps a ratio of volume to flow at different lifts is a better indicator?
Just wondering out loud...
07-18-2007, 03:32 PM
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Yeah its hard to really get all the numbers exact. And even if a shop did only a handful of people would care and even less understand what it all means.
I have almost factored that out of my thinking to some extent and go to the dyno to see which heads make the best power.
The AFR vs Dart is a great debate that is impossible to answer.
Both advertise a 205cc port and comparable flow numbers. However very few people will compare these 2 castings. Why??? In theory they have many of the same qualities, and the dart being a 62cc head from Dart gives their head a HP advantage out of the box. But how many Dart headed cars have you seen make over 450? Only a few.
Is that because they don't flow as good as they say, because they fail elsewhere in their design, or simply because they aren't as popular and therefore don't have as many cars to compare from?
We all know flow numbers don't make a head good or bad. We all like to see flow numbers, but I prefer Dyno results and track results over flow numbers or cross sectional comparisons.
I have almost factored that out of my thinking to some extent and go to the dyno to see which heads make the best power.
The AFR vs Dart is a great debate that is impossible to answer.
Both advertise a 205cc port and comparable flow numbers. However very few people will compare these 2 castings. Why??? In theory they have many of the same qualities, and the dart being a 62cc head from Dart gives their head a HP advantage out of the box. But how many Dart headed cars have you seen make over 450? Only a few.
Is that because they don't flow as good as they say, because they fail elsewhere in their design, or simply because they aren't as popular and therefore don't have as many cars to compare from?
We all know flow numbers don't make a head good or bad. We all like to see flow numbers, but I prefer Dyno results and track results over flow numbers or cross sectional comparisons.
