Intake cross sectional Area??
Intake cross sectional Area?? Considering efficiency, should the cross sectional area of your intake ports be less than or equal to the area of your throttle body?, and if that is the case, would a "larger than necessary TB" (a 92 on a 90mm intake) be considered a restriction due to air movement (basically disrupting airflow)??
TECH Junkie
Joined: Dec 2005
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Hmmmm, I have always thought of the intake manifold runner as an extension of the intake port in the head. On a 23 degree SBC I would think you would want the smallest cross sectional area of the intake runner to be larger than the pushrod pinch point in the head. That is usually the smallest CSA. This is also considering you have the proper size head in the first place.
On an LS1 style motor I would think you would want the intake manifold runner to just be a continuation of the intake port of the head with the right amount of taper.
The throttle body is another issue.
On an LS1 style motor I would think you would want the intake manifold runner to just be a continuation of the intake port of the head with the right amount of taper.
The throttle body is another issue.
So is it possible to create a stepped runner?.....something that decreases in size to eventually equal the cross sectional area of the intake port, thus increasing velocity than a continual sized runner, but then again consider flow, and velocity, what ratio would be the edge of efficiency (by ratio, I mean the difference between head intake size and the size of the runner as it enters the plenum.
I HAVE ACCESS TO A FLOW BENCH AT WORK, LETS SEE WHAT KIND OF TEST THEY'LL LET ME DO.
I HAVE ACCESS TO A FLOW BENCH AT WORK, LETS SEE WHAT KIND OF TEST THEY'LL LET ME DO.
Well, I don't know the exact answer for an intake port, but, I do kind of remember some of the math for a restrictor.
If you considered the valve to be a restrictor, find the total open area of the valve, this being the frustrum area. Then, on a perfect restrictor system you want the diffuser angle to be in the 7-8 degree range sloped back until the end of the diffuseer, the intake port, is 10 times longer than the diameter of the restrictor. Now, this is for a perfect recovery system, flowing the opposite way. But, it is how this works most efficiently. Just my $0.02!!!
If you considered the valve to be a restrictor, find the total open area of the valve, this being the frustrum area. Then, on a perfect restrictor system you want the diffuser angle to be in the 7-8 degree range sloped back until the end of the diffuseer, the intake port, is 10 times longer than the diameter of the restrictor. Now, this is for a perfect recovery system, flowing the opposite way. But, it is how this works most efficiently. Just my $0.02!!!
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TECH Regular
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From: Cleveland
Keep it in mind that the plenum is what allows the throttle body to not be 8 TIMES the area of an intake venturi. If you're running itb's, the minimum diameter of the tb Plus additional area of the throttle blade must be bigger than the venturi to keep them from becoming restrictions.
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Verdad Gallardo TECH Junkie
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Makes sense to me. Taking it a step further would not the smaller the plenum volume the bigger the throttle body should be. The reverse would be the larger the plenum volume the smaller the throttle body that can be used. 
TECH Regular
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From: Cleveland
I'm from the big throttle body big plenum school. The problem with a front breathing manifold is air distribution. The more volume you have inside, the easier it is for air to make the turn. I suppose that could make the throttle response a bit lazy, but I'm not a manifold expert. The plenums on itb style manifolds (tihink indycar) seem to be pretty small...perhaps just because they don't need to be that big. Who here has some experience with that stuff?
