318 build #2 "cost minded" for the '74 Duster

273 said

But looking how shorty headers dyno poorly compared to long tube headers to me it's got to do more with tube length and collector size than restriction.

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This is the same thing as above comparing a small to a larger cam swap under a two barrel carb on a OEM iron intake. If the header being tested is on a weak engine like the 300/360 crate engine, the header really doesn’t shine. It looks like crap. IMO, the only time a shorty should be used is ether in a Happy Days hot rod or powering a turbo. Otherwise there garbage.

That 300/360 is a production engine with a M1 dual plane and 750 carb with 1-3/4 headers. When MP changed the parts for the 380/360, it was intake cam and IIRC, larger headers.