Stock throttle body CFM ?
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 764
i'm fairly sure the stock throttle body is 48mm - a 52mm might be the limit on a stock engine. a 58mm would be overkill, and might even take away from the overall performance. i would think a 58mm TB would only meet the requirements of a highly modded engine. 
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Melting Slicks
Joined: Nov 2004
Posts: 2,799
Likes: 2
From: Cape Coral FL
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
back/day comparo
"everybody" knows that a 650 holley carb is ideal for a "mildly warmed" 350 street/strip engine...and a 750 holley is "too much" for a street 350 unless secondaries are left mostly closed, maybe even mild-mannered 454 big blocks...soooo, let's do a "worst case" and look at the 750 holley vs the "stock" tpi :
1) bore of the stock tpi throttlebod is 48mm, x 2 holes = 5.6 sq. in.
2) smallest air passage in the 750 holley is the four venturies, 1.25" dia each BUT reduced further by a 5/8" dia "booster" with a hole thru that...if for simplicity we ignore the boosters entirely, the area for the four venturies is then 4.9 sq. in.
so the "stock" tpi is bigger than the "too big" holley
"real world"...sHot Rod mag did actual strip tests with bigger vs stock tpi t-bods on a variety of stock vehicles and found no improvement on any, some were SLOWER...(i have that sHot rod feature article in my archives if you need to refer)
1) bore of the stock tpi throttlebod is 48mm, x 2 holes = 5.6 sq. in.
2) smallest air passage in the 750 holley is the four venturies, 1.25" dia each BUT reduced further by a 5/8" dia "booster" with a hole thru that...if for simplicity we ignore the boosters entirely, the area for the four venturies is then 4.9 sq. in.
so the "stock" tpi is bigger than the "too big" holley
"real world"...sHot Rod mag did actual strip tests with bigger vs stock tpi t-bods on a variety of stock vehicles and found no improvement on any, some were SLOWER...(i have that sHot rod feature article in my archives if you need to refer)
Racer
Joined: Oct 2007
Posts: 478
Likes: 1
I believe the 58mm throttle body flows around 1000cfm and the monoblade flows around 1300cfm. On a fuel injected motor I can't see where a larger throttle body would hurt anything.
On a carbureted motor you need a slight depression for fuel to flow. With FI you do not need it.
On a carbureted motor you need a slight depression for fuel to flow. With FI you do not need it.
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Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
Think of the throttlebody as a hose.
The right size hose with the right amount of pressure will squirt water pretty far. Too big of a hose with the same pressure will dribble out.
Velocity is what you need, not total CFM.
The right size hose with the right amount of pressure will squirt water pretty far. Too big of a hose with the same pressure will dribble out.
Velocity is what you need, not total CFM.
