Manifold pressure comparison in case you ever wondered

[huston marlowe]

Recently rebuilt the heat muff system with the mods to increase heated air to the carb. I wondered how the manifold pressure on the alternate combustion air system now compared to the filtered (Brackett) air system. Loss of thrust due to heated air is a given, but I didn't want to suffer additional loss because of intake system restriction on carb heat. Rigged a manifold pressure gage to the spider taps and did static and flying checks at several rpms ..Actually only did the 2300 rpm flying comparison after a more complete series on the ground. My assumption was that the air temp would have very little influence on pressure readings. The filtered air was a smooth but flat curve, while the alt. air had an inflection point..both were similar and flat enough to be within experimental error. Both had the "SAME" pressure as a function of RPM ! Sadly, I had not done a test prior to the heat muff mods. so I don't know if the stock system had more restriction than the filtered air . PS Later :: Before someone points it out ! I need to run another series with pressures taken at the airbox upstream of the carb to really see any difference in the two duct systems ! Probably need to weld boss(es) on the box at a common location if possible