Bobby,
The MAP in the plot is manifold pressure in inches of Hg. The throttle setting was not changed while the exhaust valve was closing or closed. The increase in manifold pressure results from the decreased air requirement when the rpm decreases due to the choked off exhaust. A decrease in air volume drawn out of the intake plenum along with an unchanged throttle body opening gives a manifold pressure rise.
This is consistent with what you experienced.
I’ve attached a couple of photos of the test setup.
One other observation that I forgot to mention is that with the valve even partly closed, the noise level decreased remarkably.
Steve
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bobby J. Hughes
Sent: Sunday, March 27, 2011 12:33 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Exhaust obstruction test
Steve,
Thank you for conducting this test. The attachment contains the data my Advanced Flight Systems engine monitor captured. It logs in five second intervals. A lot can happen in five seconds when the pilot is throwing switches and opening and closing the throttle. The data shows I did not re-enable the primary injector switch until after landing. So no rpm or fuel flow data was captured during most of the glide. Oil pressure indicates the prop was driving the engine. I don’t remember if I bypassed part of the super charger flow or not. The manifold pressure before the event was only 36” MP so I was not a full power. The rpm dropped from 6700 to 2500. Manifold pressure started dropping but I’m sure I was pumping the throttle and may have pulled the super charger bypass. What I don’t understand is the last seven lines of data. MP is between 18 and 29.4 at idle. This is while I was trying to taxi but could not move the plane.
Your data supports a sharp drop in rpm. Is the MAP plot EC2 fuel map or manifold pressure? If manifold pressure your test also indicates a high manifold pressure with a low rpm condition.
Bobby