Practical Engine Airflow by John Baechtel

Author:John Baechtel
Language: eng
Format: epub
ISBN: 9781613253113
Publisher: CarTech Inc.
Published: 2016-02-19T00:00:00+00:00

This Ford V-8 application has Weber carbs and tuned stacks. Carb size limits airflow at high speeds, but delivers sharp response and good torque in its intended environment.

These individual runners have a direct shot at the valve on every cylinder. This is very effective depending on the configuration of the plenum above the runners. (Photo Courtesy Mitech Racing Engines)

If the manifold/port combination supports the calculated volume requirements and runner performance is relatively equal at this point, you’ll probably find it sufficient at peak lift as well. Recall that the valve is only at peak lift for a fraction of a second, but it typically resides at or above the stated percentages for most of the valve event. These percentages represent known values relative to piston position and port flow demand for optimal VE and efficient exhaust blowdown.

You’ll likely discover that cylinder-to-cylinder flow variations are greatest with a dual-plane and least with a tunnel ram. Careful flow mapping of the manifold in this manner helps identify runners that may need individual tuning assistance. This most often takes the form of rocker ratio adjustments, individual cylinder cam lobe profiles, header dimension compensation, and even timing and jetting adjustments based on runners that exhibit weaker or uneven flow characteristics relative to the others.

Once you have created this flow map, you’ll be surprised at the follow-on thought process it provokes, all based on a keener awareness of your equipment’s characteristics and recognized methods of compensation to increase and equalize torque.

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