Posted by gmharris [71.105.36.254] on Monday, June 09, 2014 at 20:54:14 :
In Reply to: Displacement or HP? posted by Sherman in Idaho [72.47.153.28] on Monday, June 09, 2014 at 20:34:15 :
The Holley interactive carb selection app suggests that displacement and RPM are the primary factors.
Demon carburetors suggest that a carb that pulls more than 1.5 inches of vacuum at WOT is too small.
But, they have some other guidelines:
All things being equal, a bigger engine requires a larger carb. But for any given engine size:
• Higher rpm requires a bigger carb
• Higher horsepower requires a bigger carb
• Higher compression ratios require a bigger carb
• More distributor mechanical advance requires a bigger carb
• A manual-trans car can use a larger carb than an automatic-trans car
• Steeper (higher numerical) rearend gears tolerate a bigger carb
• Lighter cars can use a bigger carb
• Heavy cars need a smaller carb
• Too large a cam for the application requires a smaller carb
• With an automatic-trans car, too low a torque-converter stall-speed for the application requires a smaller carb
• Mild (lower numerical) rearend gears require a smaller carb
• Low compression requires a smaller carb
But, since our trucks usually work at the low-end of the power and RPM spectrum, smaller is better for driveabilty. You can easily make a FFPW into a more miserable vehicle to drive by putting on too big a carburetor.
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