Technocarb's Off-Road Carburetor is now obsolete and this page is for historical purposes. Do NOT contact Technocarb about buying this carburetor.
The alternative to a diaphragm-operated air-gas valve carburetor is a venturi-design carburetor. In this case, there is no restrictive gas valve to reduce the flow capability of carburetor's venturis. Technocarb made the Off-Road carburetor, which is a 4bbl venturi-style carburetor suitable for high performance applications and has an integral throttle-body using a square-bore Holley flange. To suit a variety of engine sizes, the carburetor incorporates replaceable, pressed-in venturis. At this time, the following sizes (internal diameter at the vena contracta) and approximate flows with 4 venturis. Technocarb has not flow-tested their carburetors themselves so the following ratings are estimates.
- 0.75" (400 CFM)
- 0.91" (575 CFM)
- 1.00" (675 CFM)
- 1.10" (810 CFM)
In contrast to the Impco 4bbl LPG carburetor, the Off-Road carburetor does not become leaner above its flow rating. Because of the nature of venturi carburetion, the fuel mixture actually starts off a bit lean at low flows and gradually becomes richer as air flow increases. With the Open-Loop system (i.e., no feedback fuel mixture control with an O2 sensor), the full load fuel mixture is set with a load-block valve in the hose between the carburetor and converter. A nice feature of the Off-Road carburetor is its ability to use different-sized venturis in the primary and secondary barrels - in effect becoming a spread-bore carburetor. This allows the carburetor to have small primary venturis for easy starting and low-RPM torque while having larger secondary venturis for more high-RPM power.
Going back to our 350 CID engine with 100% VE at 6000 RPM, 4 x 1.00" venturis would have a pressure loss of about 1.216" Hg and 4 x 1.10" venturis would have a pressure loss of about 0.845" Hg. Without a gas valve to limit fuel flow, the engine may be run up to any redline without a lean-out of fuel mixture.
See Technocarb 4bbl Carb Kits for more information.
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