Venturi Flow Rates
Venturi Flow Rates
(OP)
Anyone have any idea how carb companies calculate flow rates?
I took the two throttle bodies that Holley markets to GM TBI users, and calculated backwards from their rated number (CFM) to air velocity based on the area the air has to go through. It seemed like a reasonable idea, until I came up with velocity numbers which were about 30,000 ft/min apart.
My purpose for this investigation is to ensure that I am doing correct calculations for a cold air intake on my wife's Suburban. Sure, I could just throw some 4 or 6 inch tube in there, but I'd rather take the time to optimise it.
Thanks.
I took the two throttle bodies that Holley markets to GM TBI users, and calculated backwards from their rated number (CFM) to air velocity based on the area the air has to go through. It seemed like a reasonable idea, until I came up with velocity numbers which were about 30,000 ft/min apart.
My purpose for this investigation is to ensure that I am doing correct calculations for a cold air intake on my wife's Suburban. Sure, I could just throw some 4 or 6 inch tube in there, but I'd rather take the time to optimise it.
Thanks.





RE: Venturi Flow Rates
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Venturi Flow Rates
RE: Venturi Flow Rates
For the 670 CFM throttle body (2 inch bores), I came up with a flow of 184268.6 in/min = 256 ft/sec
For the 400 CFM throttle body (1.6875 inch bores), I came up with a flow of 154492.6 in/min = 214.5 ft/sec
RE: Venturi Flow Rates
John Woodward
RE: Venturi Flow Rates
two barrel carbs are rated at 3.0 inches of mercury
four barrel carbs are rated at 1.5 inches of mercury
As this is an American book, it might only be refering to American manufacturers.
Regards
pat
RE: Venturi Flow Rates
I should have said 1.5, since I did read the book once. Bad memory.
John Woodward
RE: Venturi Flow Rates
Regards
pat