What is the correct way to measure intake runner length and exhaust tube length?

Different people have different thoughts on this, but the exhaust tube length is typically measured along the centerline of the primary tubes from the head flange to where they enter the collector. And the intake runner length can be a little trickier to measure, since you have a plenum area under the carb that really is where all the runners merge together, and seemingly have an imaginary stopping point. Some use the runner wall as it stops before it blends into the plenum as the reference for the stop/start point, and others select the theoretical center of the carb footprint to represent where you start/stop measuring from. Are you considering building a sheetmetal intake and headers.

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There's no such thing as too much cam....only not enough engine!

Runner length is the length from the back of the valve along the centerline of the port/tube to a distance half the tube diameter past the end of the tube/runner. Different treatments (bell mouths and such) of the junction between the end of the tube and the atmosphere, plenum, or collector affect the effective length of the gas column.

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Joshua