Time to reach max MP?

[Mark Cline]

I would like to know, from other Bravo owners, how long does it typically take your plane to reach maximum manifold pressure after advancing to full throttle on takeoff?     

[carusoam]

Let’s invite @donkaye to the conversation…

-a-

[moxfox]

It happens instantaneously as you advance the throttle. This is of course advancing the throttle smoothly. If you cram the throttle you will get a big surge , not a good thing.

[Fritz1]

With the runway long enough I twist the throttle in, takes let's say 4-5 seconds, then full manifold pressure becomes available, accelerating to Vy the intercooler starts working and MP may increase a bit more depending how well the density controller works, putting mouse milk onto the waste gate shaft with a small brush at every oil change keeps the waste gate from sticking

[Mark Cline]

Thank you.  When I advance the throttle my MP starts climbing, and at rotation its about 35 inches.  It goes up to about 37.8 at around 400 feet off the ground.  I wanted to know if those last 2.8 inches lagging behind was considered normal.  When I get to about 1000 feet, I start backing MP down to 34 inches for climb.  My turbo and wastegate have less than 250 hours, and the exhaust system has been inspected closely by a Mooney Service Center.   Thanks.    

[Fritz1]

intercooler is kicking in, density controller may be be a tad sticky, waste gate may be a tad sticky, lube the waste gate shaft, see what that does, put the mouse milk in a small cup and apply with small paint brush to top and bottom end of waste gate shaft

[Mark Cline]

Every time the cowl is off, the waste gate gets a generous drink of mouse milk.  Does yours go all the way up to 38" by rotation?  Thanks for your help.  

[Fritz1]

no, typically 35.5 - 36.5 depending on temp, Brian Kendrick set my wastegate and test flew the aircraft thereafter, I would like to see a tad more on hot days but could not make up my mind yet to crank up the density controller, I think these density controllers have intermittent friction and are not that exact, I installed a TIT gauge to monitor the function of the density controller, and set it according to the linear diagram in the service manual, bottom line my density controller is probably set too low, however at a takeoff in Bozeman MT, about 4 weeks ago I climbed out at 37.5" at 70F 5000 ft elevation which was a tad much, bottom line those density controllers are not that exact, mine has 600h, can't make up my mind to have it overhauled, probably will work the same thereafter

[philiplane]

It takes some time for the density controller and the waste gate to get in synch as the turbo continues to spool up. Usually by 1000 AGL everything should be responding smoothly. A lot depends on the oil temperature, if you take off with it at 160 dF it tends to overshoot. The whole turbo system needs 180 dF oil to work properly.

[LANCECASPER]

20 hours ago, Fritz1 said:

With the runway long enough I twist the throttle in, takes let's say 4-5 seconds, then full manifold pressure becomes available, accelerating to Vy the intercooler starts working and MP may increase a bit more depending how well the density controller works, putting mouse milk onto the waste gate shaft with a small brush at every oil change keeps the waste gate from sticking

I wouldn't "twist" in the throttle on take-off, I use the "twist" feature vernier control for minor adjustments later in cruise. I don't shove the throttle forward either. I steadily advance the throttle smoothly, maybe a couple seconds. A CFI at Flight Safety told me back when I took initial M20M training in 1996 that the Mooney people he had observed were using way too much runway turning their throttle in rather than smoothly advancing it..

[kortopates]

Every time the cowl is off, the waste gate gets a generous drink of mouse milk.  Does yours go all the way up to 38" by rotation?  Thanks for your help.  

Expecting 38" may be the issue. Because Lycoming density controller is temperature dependent, the POH redline allows for up to 38". But normal max MAP is actually only 35-36.5" as specified in the service manual. If your going above that's it's likely set too high and not good!


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[Mark Cline]

A carbon deposit was blocking the orifice at the attachment point to the #3 cylinder.  Thus, it took longer for the correct pressure to build up in the tubing that attaches to the MP sensor.  After that blockage was removed, my MPs have much faster response rates.   

[carusoam]

Fantastic response Mark!

Thanks for sharing the details.

Best regards,

-a-