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Run to Rund · 02-12-2017, 11:38 AM

Under vacuum, 3" was used for 2 bbl since originally at WOT that was about the vacuum achieved; 1.5" was used for 4 bbl carbs. The conversion factor is discussed in Doug Roe's book, and for example the 1-3/16" venturi carbs would give 247 cfm on the 4 barrel scale, 1-5/16 about 299, and the 1.25" iirc around 280.

02-12-2017, 11:38 AM	#7
Run to Rund Senior Member Join Date: Sep 2007 Posts: 574 Likes: 6 Liked 44 Times in 22 Posts	Re: Rochester 2gc - Chevy 400 Under vacuum, 3" was used for 2 bbl since originally at WOT that was about the vacuum achieved; 1.5" was used for 4 bbl carbs. The conversion factor is discussed in Doug Roe's book, and for example the 1-3/16" venturi carbs would give 247 cfm on the 4 barrel scale, 1-5/16 about 299, and the 1.25" iirc around 280.