Not a Ford....
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Posting Guru
Joined: Dec 2003
Posts: 2,155
Likes: 3
From: Centerville, Iowa
Not a Ford....
I wanted to ask about the cfm vs engine size. My friend is running a 750 cfm Holley I believe on his 350 Chevy. This is in an 81 Firebird..not important though. I thought this was a horrendous amount of flow for such a small (relative) engine. I thought 750's were for 460's and such. Is the 750 too much? It's got a stock bottom end with more-than-likely stock-replacement pistons, stock heads, Edelbrock Performer RPM Intake, and a mild Crane cam.
On a more personal side note - would he have more hp then my 302? It's a stock 94 truck motor with bumped timing and exhaust done. I don't know..FI vs Carb...he's got the 48ci but I'm FI and have the exhaust.
On a more personal side note - would he have more hp then my 302? It's a stock 94 truck motor with bumped timing and exhaust done. I don't know..FI vs Carb...he's got the 48ci but I'm FI and have the exhaust.
Postmaster
Joined: Mar 2003
Posts: 4,038
Likes: 2
From: Spokane WA
Use this formula to calculate Required CFM:
Cubic inches X Max Rpm / 3456 = CFM required at that RPM. (given 100% volumetric efficiency)
In other words, he needs about 600 CFM at 6000 RPM, and wouldnt approach the capacity of his Carb until 7500 RPM, in summary, he is WAAAYYYY over-carbed unless he has some serious mods done to that motor.
Cubic inches X Max Rpm / 3456 = CFM required at that RPM. (given 100% volumetric efficiency)
In other words, he needs about 600 CFM at 6000 RPM, and wouldnt approach the capacity of his Carb until 7500 RPM, in summary, he is WAAAYYYY over-carbed unless he has some serious mods done to that motor.
Lead Driver
Joined: Feb 2003
Posts: 8,140
Likes: 4
From: Oak Harbor, OH
Almost all Qjet carbs were 750CFM, you adjsuted the amount the secondaries opened to regulate the CFM... I've seen them referred to as "infinite CFM carbs" on a few websites.. I'll post links if I can find them.
