It is a common fact that the fuel economy suffers unless steps are taken to improve fuel vaporization and performance. Although several approaches to improving fuel vaporization can be considered, the best one depends on the specific engine design.
Take water from the cooling system and route it through a ¼ inch copper tube wound tightly around the intake multiple runners. Then provide a return to the cooling system. You must choose the pick-up and return points to provide a pressure differential. The water will circulate through the tubing rather than just sitting there. A similar approach can be taken with exhaust gas. Install a pipe fitting in a high pressure area in the exhaust manifold, near the head and conduct the hot gas through a ½” copper tube to the intake manifold. Braze the tubing to the intake manifold runners and then connect the tubing into a low-pressure area of the exhaust system, preferably below the muffler. You may wish to pick up exhaust gas at several points with several tubes from the exhaust manifold. Alternatively, route the copper tubes inside the manifold runners. It may be necessary to use tubing smaller than ½”. The tubes must run continuously through the manifold so that no coolant or exhaust gas is cycled into the fuel mixture. Drill holes for tubing entrance and exit and after installing the tubes, braze the holes shut.
The advantage of this variant is that heat is available to vaporize the fuel mixture quickly whereas the disadvantage is that the tubes reduce the volume of fuel mixture flow to the engine, thereby reducing power at full throttle. If your car has a water heated intake manifold, it may be possible to increase the flow of hot water through the manifold heater. This can be done by increasing the size of the water entrance and exit ports. Also, installing a thermostat will help. This also improves fuel vaporization within the combustion chamber. Most engines have a heat-riser control valve. You may be able to modify the controls on it to increase manifold heating. Above all, make sure that the valve is working properly. Often it gets rusty and sticks in one position. Many engines today have a thermostatic control or flapper valve on the air filter intake, to admit hot air under certain circumstances. You can adjust the control to provide hot air to the carburetor more of the time. Then fill in the gaps. Write down the specific changes you will make to the fuel and ignition systems. Devise a plan for cold starting and raising the compression ratio that best suits your engine.
After you have converted the engine, repeat the tests you did in preparation for conversion. And don’t be afraid to keep tinkering. A little adjustment here and there may improve performance a lot.
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