jetdriven Posted December 30, 2016 Report Posted December 30, 2016 4 hours ago, Hyett6420 said: Adds about 0.5 inch in my J and approx 3-5 knots in speed depending on altitude. I can't see how a half inch of MP adds 3 knots. That's a lot. 1 Quote
ArtVandelay Posted December 30, 2016 Report Posted December 30, 2016 I can't see how a half inch of MP adds 3 knots. That's a lot. Not to mention I never saw a 1/2" bump, more like 1/10", barely noticeable using analog gauge. Curious what other J owners see? Quote
carusoam Posted December 30, 2016 Report Posted December 30, 2016 Looking at what Byron is saying.... (but using an LB POH to derive the numbers) 1" is 18 hp according to the 310hp STC... at 2550rpm at SL. It would use 1.3 gph more fuel to go with that... 0.5" would be 9hp... comparing to a similar four cylinder engine (bit of a stretch, but...) that might be 6 hp... taking it up to altitude of around 10k' would be about 3 hp extra... How fast can you go with another 3hp? Hey, isn't that what Jim just gave for an answer? If you want to test what 1/2” of MP will do... while cruising, check your Airspeed, pull back the MP a 1/2", wait a few minutes...read the airspeed again... Best regards, -a- Quote
Loogie Posted December 30, 2016 Report Posted December 30, 2016 After two years of trying to see an increase, I just don't see anything happening on the MP and I have a digital gauge as well as an analogue. Most of my experiments have been at cruising altitudes of >5k, I feel I have given that ram air a fair chance. Even Mooney folks don't believe it does anything. Any airspeed gains could be a trim adjustment etc. 3-5kts of ram air speed, I just don't think that is a reality in my Mooney (I average 158kts at cruise). Not discounting that it could probably increase the HP at low altitudes and but I just don't hang around there enough to make it a system to keep in the air. There are more bad things that come from having the system operational, the rubber seal, the door itself, the ability to ingest moist air, extra maintenance etc. I am getting my cowl redone this Feb annual, and will have that thing removed. I'll probably gain a couple knots by not having that hole in the cowl.. Loose a couple pounds in the process as well. I am also putting LED lights all around and an LED landing light. Thanks for the info guys... Quote
ArtVandelay Posted December 30, 2016 Report Posted December 30, 2016 I have literally only gone by what the mp guage and así show when it is used. No technical JPI stuff. It pops up about .5 inch and gradually if left to its own devices I get 3-5 knots on the así. Hmmm, I wonder if your air filter is more restrictive and that's why you are seeing a increase where most of us don't? Quote
jetdriven Posted December 31, 2016 Report Posted December 31, 2016 (edited) The Lo Presti cowl actually seals off the airbox from the fuel servo when the ram air is switched on. This actually pressurizes the air above ambient a little. The J model stock ram air doesn't do this. So it pressurizes the airbox too, which has a large opening with a filter at the end of it. So the best you get is the 5" of WC cowl pressure, which translates to .3" of MP. Edited December 31, 2016 by jetdriven 1 Quote
Marauder Posted December 31, 2016 Report Posted December 31, 2016 The F model ram air does produce more. On my digital MP gauge, I see 1.2" consistently. This translates into about 2 knots of speed for me.Sent from my iPad using Tapatalk Quote
carusoam Posted December 31, 2016 Report Posted December 31, 2016 Produces more or loses less... As the intake system evolved, it got better at not losing MP... My C's intake was nicely simplified. Bolt a square filter to the front of the cowl kind of simple. The R is made up of all kinds of NACA wizardry and a magnetic door for Plan B... Best regards, -a- Quote
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