Stock throttle body CFM ?
11-28-2008, 05:26 AM
#2
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. 
11-28-2008, 07:25 AM
#3
Le Mans Master
11-28-2008, 08:13 AM
#5
Le Mans Master
11-28-2008, 10:35 AM
#6
Melting Slicks
11-28-2008, 11:25 AM
#7
Melting Slicks
Member Since: Feb 2006
Location: backwoods upstate ny
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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)
11-28-2008, 01:25 PM
#8
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.
11-28-2008, 01:29 PM
#9
Le Mans Master
Member Since: Feb 2003
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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.
