31" Maniflod Pressure??

[pauldan181]

Once establishing 100 Kts. for initial climb yesterday I happened to glance at the MP gauge and saw 31". I normally
only look at the tach on TO to make sure I've got 2700 rpm after reaching full power. A big fat high pressure system has
been sitting over the Carolinas the last few days and with the altimeter setting of 30.58 I see 29.5" MP with the
engine shut down which would be about the correct field pressure (elevation 920 ft.).

Question is, Is 1.5" gain due to ram air normal? This doesn't seem right considering losses through the filter and
induction system. I have a carbed o-360 with the standard filter box.

Paul Danclovic
Jamestown NC
RV-8A N181SB

[Kevin Horton]

I've got an angle valve IO-360 with the snorkel induction system, so my data is not directly applicable to you. But, my recorded data shows the full throttle MP at 100 kt is about 0.5" higher than ambient pressure at low altitude. This is corrected for the 0.3" bias that my MP has on the ground with engine stopped.

[pauldan181]

Thanks for the data point Kevin. I'm really just trying to find out of I have an instrument error or if folks are really seeing a significant increase in MP just after takeoff.

Paul Danclovic
Jamestown NC
RV-8A N181SB

[DanH]

Originally Posted by pauldan181

Question is, Is 1.5" gain due to ram air normal?

Sorry....the maximum available dynamic pressure at 100 knots and 1000 msl is 0.465" Hg.