Rotary Tech Tips: Additional Tuning Tips (2024)

1. Although there is a fuel filter (which should be changed regularly) near the stock fuel pump, the addition of a second filter (i.e. Fram G-12) just before the carburetor is good preventive maintenance.

2. Good quality unleaded fuel is best for spark plug life. In racing, it is desirable to use moderately high octane fuel (95 to 105 octane) although even 90 octane may suffice. More important is the "vapor pressure" of the fuel, especially in warm weather and at high altitudes.

The higher the vapor pressure, the easier the fuel boils. It is possible, indeed common, for fuel to boil in a carburetor float bowl. When it does, the mixture is leaned out and performance suffers. This problem is most severe in the spring, when many local service stations still have "winter gas". This gas is very volatile for good cold-starting, but can be potentially troublesome. For serious racing, use race gas only, and ask the supplier about the vapor pressure of his fuel. If he is vague, find another supplier.

3. In general, rotary engines are not damaged by running too rich or too lean. They may or may not misfire noticeably, but power and mileage do suffer. In street driving, a lean mixture can sometimes be felt as "surging" at a steady cruise throttle.

4. If you experience a "jerkiness" on deceleration between 2,000 rpm and idle, it is usually due to lean misfire. This jerkiness can be alleviated by lowering the idle speed and richening the mixture slightly. Old spark plugs or mistuned ignition systems also aggravate this problem.

5. A well-designed cold air box with ram air intake can add 3 MPH to a car’s top speed. We recommend feeding the box with two four-inch diameter hoses or one six-inch diameter hose.

6. A rotary engine must have an effective air filter at all times. This necessity is also true of cold air box/ram air intake systems. Without an effective filter, rotor seals, side housings, and rotor housings can be damaged very quickly.

Intake Length

Intake length tuning can be very sensitive on race engines and mildly sensitive on street engines. It is common that a 3/16-inch change in intake manifold length makes a notable change in the power curve. The basic characteristic is essentially the same as a reciprocating engine: longer passages move the torque and horsepower peak down the RPM range, and shorter passages do the opposite. In addition, as the intake is shortened, the power band becomes narrower and the peak a bit higher. However, depending on the application, this may be undesirable.

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