Those who have heard it before I am repeating so bear with me. Jeff and all netters reading: There is NO FUEL ECONOMY savings with fuel injection! You are only changing the way that the fuel is delivered and its accuracy, so it helps in overall horsepower and torque, but does not make ANY better fuel economy. To get the increases people are used to seeing advertised with fuel injection requires additional spark advance at appropriate time, and more exact fuel metering than we are talking about in aviation. This requires a feedback computer system to make this possible and has been much discussed here, so I will not go there with this post. Throttle body heat IS necessary for fuel injection in the off chance that conditions do occur that cause icing around the throttle plate. On certified aircraft you will see alternate air, which is heated to handle this possibility. Autos avoid this necessity by providing coolant heat at the throttle body, and by designing the engine to operate at a higher temp of 195-205 regulated by a water thermostat. Most still have some form of heated air on startup, or throttle warming. This is because the best mix of fuel and air occurs at a warm temperature, so too cold allows the fuel to condense on intake walls and separate, which is why so many use port fuel injection to avoid this.
Stick to carbs: much more simple and easy. The pattern to follow is already there.... Scott, in William Wynne's book he evaluates the 140, 160 & 180 horsepower heads and finds that although they provide the proper increase in performance for cars; in the ranges of rpms, and use in direct drive applications are bad to use in planes. They increased quench area which can lead to detonation, and larger valves actually cause a DECREASE in performance at lower rpms, in favor of rpms over 3000, so that it is not practical for us. Larger valves will not increase lower rpm performance due to the drop in vacuum signal to the intake, so it will take higher rpms to get the power increase. Same with bigger exhaust. Increase is only realized above the rpms where we intend to use the plane/engine. Doug Roe makes a great case for this by running his competition Camaro on first a 650 cfm carb, and then an 850 cfm carb, and was faster on the 650. More air is good to a point; if the velocity of that air drops below a certain point, no performance increase is realized in lower rpms, but are in upper. This why the OT10 cam works better than all others: they stay closer to stock with duration and increase lift, while others try to increase both which actually cause a loss in power in the lower rpms in favor of the upper end. A quick look at the Summit Racing Catalog on cams will show the effective rpms for cams designed with more lift AND duration. Colin KSFB
