I'm building a sb2.2. Cross sectional area at the intake face of the heads is around 3.25 inches, and looks to be about that size all the way to the intake valve.
For maximum horsepower, should the runner entrance under the carb in the intake manifolds match this, be smaller, or be bigger?
Cross sectional area
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Re: Cross sectional area
Bigger.
Paul
Paul
"It's a fine line between clever and stupid." David St. Hubbins
Re: Cross sectional area
No idea about sb2.2, probably something good and this is just a general observation..
Bigger, ok, although we still need to choose the grinder wisely. A thinner one may have fewer functions and be less efficient throughout the RPM range, but without the added lenght the bigger grinder may actually be lighter
-juhana
Bigger, ok, although we still need to choose the grinder wisely. A thinner one may have fewer functions and be less efficient throughout the RPM range, but without the added lenght the bigger grinder may actually be lighter
-juhana
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A balanced person dares to stagger, and modify ports bigger
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mag2555
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Re: Cross sectional area
A general rule of Thumb is to have the runner expand 2% per inch of runner lenght.
This will not harm, but it might not be the best either, as a example I offer this from my personal experience 30 years ago.
On a local buddy of mine SB mopar Brodix heads that I ported up for a second time due to the stroking of his motor I also flow tested a new Intake he was running but I never got to test out a long with the heads before this time.
Upon getting my hand on the Intake I was struck by how much expansion rate the runners had and said to myself this must be excessive, I am talking like the runners expanded a easy total of 1/2" from the flange to the plenum.
When flow testing both the heads and Intake together I found that if brought down the expansion rate I picked up 25 to 30 cfm.
I then set about to close up the runners with epoxy and give the Intake back to buddy to run at the strip that Sunday.
On Sunday evening he called me to say that the car lost near a full second in ET!
During the following week I chiseled and ground out the epoxy , he bolted the Intake back on that next Saturday at the track and all the lost ET right came back!
In short without a heck of a lot of flow bench time tracking velocity of the whole Intake side of the motor a long with calculating what the port area needs to be to average out the velocity profile that works best in the motors power band to not exceed 350 fps is the type of work that needs to be done to answer your question the best.
This will not harm, but it might not be the best either, as a example I offer this from my personal experience 30 years ago.
On a local buddy of mine SB mopar Brodix heads that I ported up for a second time due to the stroking of his motor I also flow tested a new Intake he was running but I never got to test out a long with the heads before this time.
Upon getting my hand on the Intake I was struck by how much expansion rate the runners had and said to myself this must be excessive, I am talking like the runners expanded a easy total of 1/2" from the flange to the plenum.
When flow testing both the heads and Intake together I found that if brought down the expansion rate I picked up 25 to 30 cfm.
I then set about to close up the runners with epoxy and give the Intake back to buddy to run at the strip that Sunday.
On Sunday evening he called me to say that the car lost near a full second in ET!
During the following week I chiseled and ground out the epoxy , he bolted the Intake back on that next Saturday at the track and all the lost ET right came back!
In short without a heck of a lot of flow bench time tracking velocity of the whole Intake side of the motor a long with calculating what the port area needs to be to average out the velocity profile that works best in the motors power band to not exceed 350 fps is the type of work that needs to be done to answer your question the best.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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mag2555
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Re: Cross sectional area
Junhanaa, I think you misread what the OP is asking about in this post!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
Re: Cross sectional area
You probably would end up around 4.5" on long runners and 4.200" on short runners on plenum openings .Taper this down from there to your 3.25"It all would depend on manifold runner length and intake used,and intended rpm.
Re: Cross sectional area
Probably, but so far it appears he might need some grinder though.
-juhana
A balanced person dares to stagger, and modify ports bigger