FBO/Quick Fuel Carburetor Size and Series Chart

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RPM Shift Point to Carb Size

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Note: This is only a rough estimator of carb sizing.  Volumetric efficiency, gear ratio, compression ratio, valve size and lift, weight of car, convertor stall and other factors may vary the carburetor sizing so before you make your selection always contact us for and speak to a reliable carburetor professional who is familiar with Quick Fuel air flows and the various types and series of carburetors available. 

Cubic Inches 5000-5500 5500-6000 6000-6500 6500-7500 7500 +
260 to 375 500-650 650 650 750 850
Up to 420 650 650 750 750-850 850-950
Up to 500 750 750-850 850-950

950-1050

2 x 650

1050

2 x 650

Up to 540 850 850

950

2 x 650

1050

2 x 750-850

1050-1150

2 x 850-1050

600 and Up 950

1050

2 x 750-850

1050-1150

2 x 850-1050

1150

2 x 950-1050

1250

2 x 1050

 

Street/Drag Carburetors Series Selector

Note: When selecting a Series of carburetor keep in mind that if your select a carburetor that is is too low of a series you may have tuning issues.  Selecting a series that is one step above the recommended will not cause tuning issues and in most cases will make the fine tuning easier.  Carburetors are very sensitive to at Idle Vacuum signals and a low vacuum signal may cause the carburetor to run very rich at idle and part throttle cruise.  A excessively rich condition can cause serious engine damage.  You have a big investment in your performance engine don't risk your investment to save $50, get the right series and size the first time, always consult with us before making your final decision.

Cam Duration/ 50  HR Series SS Series Q Series Race Q QFX Series
200-214 X X      
212-220   X      
220-230     X    
232-248     X X  
248-260       X X
260 +       X X

The last thing you want for your Street Hot Rod, Weekend Warrior or Drag Race car is a carburetor based solely on the lowest price.  Now is not the time to try and balance your build budget with a poorly made, mass produced, chrome plated inexpensive carburetor.  Get the right one the first time and then drive it like you stole it!

When you call us be prepared with all the details of your fuel delivery, ignition system and timing events.  A carburetor can never be tuned to it's optimum potential if the timing events are not correct for the engine/car combination. With over 90 years combined experience as carburetor/ignition tuners Jim and I will always help you to achieve the best tune-up, highest performance and longest possible life from your investment whether it's on the street, track or both.

Approximate Initial Timing Events Based on Cam Duration at 50

Based on Cam being correctly chosen based on all engine spec's

With correct Fuel Octane for Compression Ratio

 

Initial Idle Timing

10-14 12-16 14-18 18-22 22-24 22-26  24-28 26-30  28-32 30-34 Lockout
Cam Duration/ 50                      
200-214 X X           W/Vac      
212-220   X X         W/Vac      
220-230     X X       W/Vac W/Vac    
232-248       X X       W/Vac    
248-260           X X X      
260 +               X X X X

Rule of thumb....any performance engine that will generate 10" or more of vacuum at idle with 30* of timing at idle RPM will benefit greatly from a vacuum canister connected to a constant manifold vacuum source.  This requires that the distributor be properly curved and phased to the application and the Vac can set up with limiters.

Your 60's/70's performance engine was designed to run on High Octane Leaded fuel, you're now feeding it Low Octane Camel Spit with a side of ethanol.  Changes must be made to the ignition timing events to make it run properly even if it's a factory stock engine. 

When your ready to call us please have as much of the following information as possible :

Cam duration at 50

Gross lift at the valve

Rocker arm ratio

Compression Ratio

CID

Head Type and valve size

Head flow if possible

Car weight

Gear Ratio

Convertor stall

Trans type (OD?)

Max Shift RPM

Current carb type and size

Fuel Pump Brand and Size

Filter types and location in fuel system

Fuel Line sizes from the cell to the float bowls

Inches of Manifold vacuum with idle timing set at 30* with or without Vac line connected

Type of distributor ...with or without vacuum canister.
Ignition box- Daytona CD1, Crane, MSD, stock?

Dual or Single plane intake

Headers and tube size

Race Car? 60' times, ET and MPH?

Current initial and total timing numbers and what issues you're having.

 

Give us this and we'll give you the optimum Quick Fuel Carb the 1st time.

 

TECH TIP: Is my carb too big or small?

Connect a vacuum gauge to a constant manifold vacuum source and attach it to the dash in plain view, make a pass.  At the stripe look at the gauge if it reads more than 1-1.5" the carb is too small if it's less than 1" it's too big.

 

Carburetor sizing

Quick Fuel Specials

Complete Quick Fuel Carburetor Catalog

Carburetor CFM Calculator

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Please call for Special Reseller Pricing  541-942-5920

Email tech@4secondsflat.com

 

541-942-5920

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