Originally posted by GoppelDanger:


Which one has more interior surface area?
Does high boost on a dual plane manifold with no secondaries do anything between the two sets of runners?
How do these factors affect air velocity?


Ideally, one would just create a single oval chamber above the "V" and have short runners to the heads. That is the best thing for forced induction. You just need to make sure the injectors fit, too. The plastic oval intake is the closest thing to that configuration.



I don't know, you tell me!

As far as the surface area, I can sort of answer that:

Twin port, assuming 34 and 36mm (avg. guess) diameter runners of length L:
(34*Pi*L + 36*Pi*L) = 70*Pi*L

Ovalport, 57mm long by 23mm thick, or broken down to one circle and one rectangle where we take the surface area of the cylinder and just the two long sides of the rectangle:
(23*Pi + 34*L +34*L) = (23*Pi+68)*L

So lets assume that L of both intakes is equal, then:
S<split>= 220*L mm^2
S<oval>= 140*L mm^2

But to me, in this particular case, the surface area is much less of a factor influencing flow since they are on the same order of magnitude and therefore is not as relevant to our FI flow as the cross sectional area would be.

Cross sectional area of oval port:
(23*Pi/2)+(34*23) = 1197mm^2

Cross sectional area of split port:
(18^2)*Pi + (17^2)*Pi = 1926mm^2

% Larger cross section = 1926/1197 = 1.61 or 61% MORE cross sectional area.

% more S area = 220/140= 1.53 or 53% MORE surface area.

ratio of cross section to surface area (split) = 8.75
ratio of cross section to surface area (oval) = 8.55

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My analysis of these numbers:
Okay, the split port has more cross sectional and surface area than the oval but that doesn't tell the whole story. These last numbers, the ratio of cross section to surface area show that the split port has a higher cross section to surface area ratio.

A true circle will have the best ratio of cross sectional area to surface area which approaches 9.0

Obviously the circle or cylinder is the most efficient shape for maximizing this ratio, we can indirectly see this in all kinds of piping as well.
This would be a good indicator of the Through-put of the piping system I think because it kind of reflects drag vs. volume if you assume the pipe roughness was equal and that the velocity of the airflow is the same (mass/time through the pipe).

So the split port has a better ratio than the oval port in this case, but they are pretty close so as I said I wouldn't let that bother me.
What does tell the story is the MUCH higher cross sectional area of the split port.
That means that assuming the drag is close to the same, it can flow near 50% more air volume than the oval.

Or at least that is what these numbers are telling me.

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black