231 Idle Manifold Pressure

[N231BN]

231 Owners/Pilots,

 

What is your approximate MP at 1000-1200 RPM? Most engines will come down to around 10" but my -GB goes no lower than 17-18. Maybe it's a turbo thing, it has been a few years since I was flying the 414 so I don't really remember.

[carusoam]

When the MP line is leaking, it tends to become a barometer....

Do you have a mechanical MP gauge with a calibrated weep hole?

If the MP were really 17 when you are expecting 10", the engine would not be idling, or running very smoothly...

At 17" of MP, the O is able to maintain level flight.

Your power management will be challenging with faltering MP instrument.

I'm not a turbo pilot, but the signs are pretty strong to be an MP gauge issue.

Best regards,

-a-

[N231BN]

When the MP line is leaking, it tends to become a barometer....

Do you have a mechanical MP gauge with a calibrated weep hole?

If the MP were really 17 when you are expecting 10", the engine would not be running very smoothly...

Your power management will be challenging with faltering MP instrument.

Best regards,

-a-

 

I just installed an overhauled mechanical gauge after getting rid of the Aerosonic MP/FF combo. No change from before.

 

I have been trying to find out why my 231 is a little slower than what others are reporting. If I had a MP line leaking I would be going faster than normal as it would take more power to achive the same 32" on the gauge. I thought maybe the gauge had a leak in the aneroid, I haven't been up to altitude yet with the new gauge so it could be fixed.

[N231BN]

I have a friend with a '67 Exec that had always said it was a slow airplane. I flew it once and noticed the MP wouldn't go below 15 at any low RPM. I discovered that the small aluminum MP line had several spots where it was corroded through and when I tried to remove it the line broke into three different pieces. Needless to say that fixed his speed issue. Now he complains how much more gas it burns...

[Guest]

You should be able to do a pitot static type test to the MAP line from the engine end of the line. Drawing vacuum on the line should be the same 1"Hg per 1000'. Stopping the vacuum anywhere during the test should hold steady.

Clarence

[Openwheeler3]

My rocket is the same way, won't go below 15 or 16 inches on the ground. In flight it will go lower, like 10 or 11 I think. Must be a turbo thing.

[jackn]

I also idle around 17"

[Mike A]

I also idle around 17"

 

+1

[carusoam]

The 60’s MP line is about 1/8" dia, flexible, soft, aluminum tube. It has a calibrated hole drilled in it about two inches from the gauge.

If a vacuum was put on the engine end, as Clarence outlined above. It would not hold the vacuum. Air would slowly leak in through the weep hole.

Side question: without a weep hole, how does the MP gauge not fill up with blue goo over time?

Do you modern guys have a separate sensor for MP with wires going to the instrument?

Best regards,

-a-

[N231BN]

+1

Thank you!

[Guest]

The 60’s MP line is about 1/8" dia, flexible, soft, aluminum tube. It has a calibrated hole drilled in it about two inches from the gauge.

If a vacuum was put on the engine end, as Clarence outlined above. It would not hold the vacuum. Air would slowly leak in through the weep hole.

Side question: without a weep hole, how does the MP gauge not fill up with blue goo over time?

Do you modern guys have a separate sensor for MP with wires going to the instrument?

Best regards,

-a-

You're 100% correct, for those installations with a drain/weep hole in the line it will not hold vacuum. You will need to test beyond that line.

Clarence