Racing Carburetor and Manifold Calibrations

A most difficult thing in racing engine development is to understand fuel distribution among the cylinders and get it correct in the engine at the race track. Fuel distribution is also an area where small changes can result in big gains or big losses. The only accurate way to determine what these small changes should be is to use a dynamometer with mixture level analysis on each cylinder. The purpose of this tune-up manual is to relay to the racers the fuel distribution information accumulated over the years from Chrysler dynamometer development programs.

Fuel distribution is the cylinder-to-cylinder variance in fuel-air ratio. It is desired that the cylinder not be too lean or too rich and that all the cylinders be the same fuel-air ratio through the engine speed range. It is obvious from this that the carburetor and intake manifold work as a team. A stock carburetor that works well on a stock manifold may not work well on a race intake manifold. A race carburetor that performs well on a race manifold may perform poorly on a stock manifold.

In most cases, drag racing requires certain changes to be made to any carburetor and special manifold modifications to go with the carburetor that is to be used. These modifications have been determined on the dynamometer for the best overall engine output for Super Stock, Modified Production and Bracket racing. The most popular racing packages with the commonly available manifolds will be covered by engine family, i.e. 6 cylinder, LA engine, B engine, RB engine and Hemi.

This revision supersedes all previous information. This bulletin represents the latest developments that our dynamometer and drag strip testing have shown to work. Many carb-manifold packages are left in for reference only. It's the latest information that we may have on an out-dated package.

A. C. Nichols & L. S. Shepard Staff Engineers

Package:		4 Barrel Set-Up General Multi-Purpose
Carburetor:		Holley List 6299
Manifold:		Offenhauser Aluminum 4 Barrel PN P3690801
Manifold Modifications:	None
Carb Specifications:	390 cfm Holley, vacuum secondaries
Primary Jet:		#49
Secondary Jet:		#52
Power Valve:		25R-591A-65
PV Channel Restriction:	.052
Idle Air Bleed:		.078
High Speed Bleed:	.043
Diaphragm Spring: 	Yellow

This is the best general purpose four barrel setup for the 6 cylinder engines.

Package:		4 Barrel Set-Up Race Only
Carb:			4 Barrel Holley List 7191 PN P3690930
Manifold:		Offenhauser Aluminum 4 Barrel PN P3690801
			Exhaust Heat Blocked
Manifold Modifications:	Car mounted with primaries toward the front of engine. See Figure 21-1.
Carb Specifications:	600 cfm Holley, double pumper dual feed with mechanical secondaries - Manual Choke
Throttle Bore:		1-9/16 x 1-9/16
Venturi:		1-1/4 x 1-5/16
Primary Jet:		#64
Secondary Jet:		#72
Power Valve
Channel Restriction:	.046
Power Valve:		No. 65
Pump Shooter:		Primary - .025
			Secondary - .021

Note: For general multi-purpose or brackets, the previous carb set-up is recommended. This package is for all-out racing only.

Package:		2 Bbl. Set-up with Headers
Carb:			2 Bbl. Carter BBD-81375
Manifold:		Production Aluminum
Manifold Modifications:	None required.
Carb Specifications:
Throttle Bore:		1-7/16  Primary Jet: 2 Steps Richer
Venturi:		1-1/16  Secondary Jets: N/A

Package:		Hyper Pak Four-Barrel
Carb.:			Carter AFB 3083 PN 2129881 (No Longer Available)
Manifold:		Chrysler Aluminum Hyper Pak (No Longer Available)
Manifold Modifications:	See Figure 21-2.
Carb Specifications:	Carter AFB
Throttle Bore:		1-7/16 x 1-9/16
Venturi:		1-1/16 x 1-1/4
Primary Jet:		120-389 (.089)

		Throttle Side		Choke Side
Secondary Jet:	120-350 (.050)		120-365 (.065)

			WOT 	PT
Metering Rod:	16-51 (.060 x .065)

Float Setting:		9/32 Inverted - Measured from float bottom to gasket.
Accel. Pump Shooter:	.028
Idle Feed:		035

Special Note: This carb and intake manifold system has the primaries of carb facing toward the engine See Figure 21-2.

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