Carb and intake question.
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Posting Guru
Joined: Feb 2013
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From: Sunny Florida
Carb and intake question.
Pulling my engine to be sent to the machine shop to be built. Turning the worn out 302 into a peppy 306 with a mild street cam. Goal is around 300hp and just as much torque. For now the stock heads will be ported and polished, maybe in the future I will go to a better flowing head. My big question is about carburetor and intake. Starting with the carb... How do I figure how many CFM the carb should be? Second question is for the intake. Single or dual plane? What is the difference?
Hotshot
Joined: Apr 2009
Posts: 14,333
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From: Stanley, VA
In a dual plane manifold the flow is divided. Two cylinders on one bank and two cylinders on the other bank are fed by half the carb. In a single plane manifold, there is a plenum chamber under the carb and all eight cylinders feed from the plenum.
Dual plane offers more driveability and bottom end. single plane better for top end.
Carb size, a lot of variables. Cam, compression, rear gearing, compression, max RPM, all affect the carb size. For a starting point I would go with 600cfm and vacuum secondaries.
Here are the two manifolds, first is the dual plane.
Dual plane offers more driveability and bottom end. single plane better for top end.
Carb size, a lot of variables. Cam, compression, rear gearing, compression, max RPM, all affect the carb size. For a starting point I would go with 600cfm and vacuum secondaries.
Here are the two manifolds, first is the dual plane.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
I suggest referring to a carb sizing calculator: http://www.summitracing.com/expertad...cfm-calculator
A street small block would range from 500 to 650 cfm. Assume 85 percent volumetric efficiency.
In terms of intakes, a single-plane is for high RPM use. On the street (and a heavy truck), torque is the name of the game so stick with a dual plane.
Many choices out there.
A street small block would range from 500 to 650 cfm. Assume 85 percent volumetric efficiency.
In terms of intakes, a single-plane is for high RPM use. On the street (and a heavy truck), torque is the name of the game so stick with a dual plane.
Many choices out there.
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