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Header primary sizing
Pull CID geometry and peak RPM from engine tools when saved.
Shared build memory
CID + peak RPM for primary rough-size. Optional bore/stroke/cyl.
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~2.125" OD tube class
Calculated primary ID ≈ 1.947 in · 350 CID (43.8 / cyl)
Balanced street/strip primary length.
Rule-of-thumb gas-speed sizing — not a wave-tuned dyno substitute. Chassis clearance, flange pattern, and collector design matter as much as tube OD.