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How to Supercharge a Carbureted Engine

Anybody with a modicum of mechanical aptitude can bolt an old-school "roots" type supercharger onto an engine, slap a carburettor on top and call it a day. Roots blowers look cool sticking through the bonnet of an old muscle car but can't keep up with the centrifugal superchargers popular today. Centrifugal blowers are mechanically identical to turbos but use a belt drive instead of hot exhaust gases to spin the compressor wheel. Carburettors were at one time almost useless for these applications--driveability was poor, and engines tended to explode. However, the newest generation of specialised "blow-through" forced-induction carbs can easily rival fuel injection for power and reliability.

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  1. Read the supercharger kit instructions--exact installation procedures will vary greatly by engine and kit. You'll need to install the supercharger bracket in place of the existing alternator bracket, install the new supercharger pulley on the crankshaft, bolt the supercharger to the bracket and connect the supercharger to the crankshaft with the supplied belt.

  2. Remove the old carburettor and bolt the forced-induction carburettor in place. These carburettors use modified internals to increase fuel flow according to boost. This crucial characteristic is what makes modern blow-through supercharger applications (so-called because the supercharger blows through the carburettor) different from those of days gone by. Without this ability, the carburettor would either run too fuel rich when off boost or too lean on boost.

  3. Install the round "hat" on top of the carburettor. The hat sits where the air cleaner would otherwise be and links the carburettor input to the supercharger ducting. If you have the space under the bonnet, use an L-shaped piece of tubing to duct air into the carb instead of a hat--the L-tube will not hinder flow at high RPM and/or extreme boost levels.

  4. Connect the hat or L-tube's input tube to the supercharger's output tube with the kit's supplied aluminium tubing, silicone couplings and hose clamps. If you're using the optional intercooler, you'll connect the carburettor to the intercooler output and the intercooler input to the supercharger output.

  5. Tip

    If you're running anything more than 10 PSI of boost, you'll need to upgrade to a higher pressure fuel pump. Boost pressure will push back against the fuel in the lines; if boost pressure gets too close to the pressure in the fuel lines, the fuel flow will stop, and the engine go bang. A fuel pump designed for electronic fuel injection will maintain 70 PSI all day long, allowing you to run a return-style fuel pressure regulator and keep the carburettor fed at any boost level. For ultimate control, use a boost referenced pressure regulator that will automatically increase fuel pressure one-to-one with boost pressure.

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Things You'll Need

  • Metric and standard sockets, full set
  • Wrenches, full set
  • Phillips and flat head screwdrivers
  • Specialised blow-through, forced-induction carburettor
  • Centrifugal supercharger kit designed for your engine
  • Blow-through carburettor "hat"
  • Supercharger-to-carburettor plumbing and fixtures

About the Author

Richard Rowe

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

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