LoPrestis Cowl on a M20J

[JayMatt]

So, In the middle of my restoration project on my M20J, I discovered the LoPrestis Cowl mod. A few searches on here and it seems a few have done it and it does increase speed and whatever else at a pretty substantial price. The thing that peaked my interest was the fact that it discusses the RAM air or the SCRAM air on the LoPrestis cowl. My M20J doesn't have a RAM air. Is this odd to anyone? The cowl with the rectangle holes in it is the one that I have and it looks like the RAM air was bondo'd over. I can't find any linkage in the plane to indicate there ever was RAM air. 

 

So I would like any knowledge on the matter from those that know. Mines a 78. Is this unusual? Seems the LoPrestis cowl would be even less valuable seeing as the RAM air gives that extra manifold pressure. Or maybe it would be way more valuable because I would install one? 

Just to dig deeper in the matter, Can I install one with my current cowl and would there be any benefit to that? 

[mike_elliott]

very minimal benefits to ram air on a J. The Bennie of the LoPresti is mainly cooling without a speed penalty

[EricJ]

15 minutes ago, JayMatt said:

So, In the middle of my restoration project on my M20J, I discovered the LoPrestis Cowl mod. A few searches on here and it seems a few have done it and it does increase speed and whatever else at a pretty substantial price. The thing that peaked my interest was the fact that it discusses the RAM air or the SCRAM air on the LoPrestis cowl. My M20J doesn't have a RAM air. Is this odd to anyone? The cowl with the rectangle holes in it is the one that I have and it looks like the RAM air was bondo'd over. I can't find any linkage in the plane to indicate there ever was RAM air. 

 

So I would like any knowledge on the matter from those that know. Mines a 78. Is this unusual? Seems the LoPrestis cowl would be even less valuable seeing as the RAM air gives that extra manifold pressure. Or maybe it would be way more valuable because I would install one? 

Just to dig deeper in the matter, Can I install one with my current cowl and would there be any benefit to that? 

The later J models don't have ram air from the factory, and Mooney put out a "delete kit" to remove it from older J model airplanes.    Since the ram air does almost nothing on a J model and there are down sides to having it or maintaining it, so many have since deleted it.   I deleted it on my airplane.

Be glad somebody already did yours. 

[KB4]

Sounds like someone did a Ram Air delete instead of buying a 30 gasket and some LPS2.  Gives 1/2-1” increase in MP.  

pull 2 screws on annunciator panel, my bet is bulb for Ram Air is missing  throw 1 in there, if it lights up, you had Ram air b4  

 

 

[Shadrach]

Ram air originated on the E and F models in the 1960s. It was carried over to the early J models even though the filtered intake was completely different. The standard narrative is that the  E/F model filtered intake was lousy and the ram air was a Band-Aid. The redesigned filtered intake on the J was supposedly so much better That Mooney was able to eliminate the ram air after a few years because it made no difference. 

I own an F model and have never noticed that it is strangled by its intake design compared to other aircraft.

There is no question that the SCRAM air on the Lopresti cowl will boost MP above ambient. What is in question is how much. No one has done a sophisticated test, so we’ve no data other than the manufacturer’s claims.

I’ll add that I’m skeptical that the 201 intake is so good (or the E/F’s so bad) that it negated the benefits of Ram Air. My take is that eliminating ram air was an easy money saver that could be marketed as superior engineering. 

[A64Pilot]

I can tell you that on my J that does have the ram air, there is no significant difference that I can see airspeed wise.

In my opinion the return on investment of a Lopresti cowl just isn’t there and it could be argued that it may hurt resale as some won’t trust why it’s there and others want “factory”, so your buying number of people is greatly reduced. Me I wouldn’t pay extra for it and I’d want to ensure it was correctly done installation wise.

My J in Fl has no issues with cooling even in August, I never even get past 2/3 of the green cyl head temp wise, but I also climb about 110 kts too.

[KSMooniac]

Your plane definitely had ram air, and it definitely did not help, and a previous owner deleted it, like many of us have.  It's not worth the squeeze on a stock J.  The ram air on a LoPresti J Cowl DOES give a noticeable boost, though.  Whether the LoPresti cowl is a worthwhile investment for you is up to you... there are ~40 hours or more involved in the installation, not including paint.  But it is much nicer.  If your cowl is significantly worn, if your nose gear doors are worn or damaged, then you might end up talking yourself into it.  @testwest did some extreme drag reduction on his '77 J, including the LoPresti cowl, and regularly flew at 165 KTAS at 10 GPH.  That is the best I know of in a J!  It takes a lot of effort to get there.

[Shadrach]

51 minutes ago, A64Pilot said:

I can tell you that on my J that does have the ram air, there is no significant difference that I can see airspeed wise.

In my opinion the return on investment of a Lopresti cowl just isn’t there and it could be argued that it may hurt resale as some won’t trust why it’s there and others want “factory”, so your buying number of people is greatly reduced. Me I wouldn’t pay extra for it and I’d want to ensure it was correctly done installation wise.

My J in Fl has no issues with cooling even in August, I never even get past 2/3 of the green cyl head temp wise, but I also climb about 110 kts too.

MP gauge would be primary for ram air not ASI.  

The real world benefit that I personally see from ram air is the opposite of what you would think. It’s most useful at low altitudes because I can run more fuel through the engine while LOP. Opening the Ram air at a DA of 3000ft provides enough additional air to the engine that EGTs on the lean side drop by 30-40°.
 

Put another way. If I set up 25° LOP cruise at a DA of 3500’ and then open the ram air, I will then need to enrichen the mixture sufficiently to raise the EGTs back my original setting. Is it a lot? Not really but it’s good for a few knots.

As for the Lopresti mod not worth the cost.  You could make that argument for every speed mod. However I have seen this man in the flash and it is most definitely an upgrade over the factory cowl. Slicker design, better engine access and excellent fit and finish. I would consider paying a slight premium for it during a purchase More importantly, if comparing two machines that were otherwise equal I would certainly go with the Lopresti cowled bird over stock and I think must educated buyers would also.

[ArtVandelay]

My 78J had ram air, with analog gauge you’d see a slight blip of the needle, barely noticeable. What you “lose” in extra power is countered by improved aerodynamics of the front of the cowl without the hole.
It’s one less thing to worry about…I’ve never missed it.
Since I don’t have it, this makes getting the LP cowl a non starter.

[1980Mooney]

Whelen bought LoPresti.  The WAT website no longer shows any Mooney cowl mod.  It only shows cowl mods for the Piper Seneca and Twin Comanche.  Maybe they will do it or maybe the entire discussion is moot.  As the Mooney fleet ages and shrinks the mods and STCs continue to get abandoned  - its just supply and "no demand" economics.

https://flywat.com/collections/cowl-aircraft-mods

Edited December 14, 2022 by 1980Mooney

[JayMatt]

11 minutes ago, 1980Mooney said:

Whelen bought LoPresti.  The WAT website no longer shows any Mooney cowl mod.  It only shows cowl mods for the Piper Seneca and Twin Comanche.  Maybe they will do it or maybe the entire discussion is moot.  As the Mooney fleet ages and shrinks the mods and STCs continue to get abandoned  - its just supply and "no demand" economics.

https://flywat.com/collections/cowl-aircraft-mods

I understand. My question was more around the RAM air Mod than the cowl. I don't need an extra 5-7mph for 13k I can fly a lot of first class direct flights for that. I was just curious if I should consider putting a RAM on or not. 

[Bolter]

For the record, this is the RAM Air Delete instructions, if it helps reassure you that the delete was legit.  Of course, it should be in the logs, as well, referencing this document. 

I had a video from my J, opening and closing the ram air, while watching the MP. Just a blip from the "shock" then returning to the original position.  If I find the video, I will edit this post and add it. 

-dan

ram air removal M20-93.pdf

[KSMooniac]

41 minutes ago, JayMatt said:

I understand. My question was more around the RAM air Mod than the cowl. I don't need an extra 5-7mph for 13k I can fly a lot of first class direct flights for that. I was just curious if I should consider putting a RAM on or not. 

You should not re-install the factory style ram air on a J cowl.  LoPresti completely re-engineered the cowl, intake, nose gear doors, etc. into a well-optimized package to make their ram air system actually work.

[A64Pilot]

Today, coming back from Deland from lunch at 1500’ 23 squared 140 IAS and 8 GPH it made a little less than .5” MP, fuel burn increased from 8.0 to 8.2 or three, I didn’t see how much if any increase in speed as it was bumpy and you don’t get meaningful results unless in glass smooth air. MP and FF though is nearly instaneous. I was not at full throttle, perhaps it would have more effect if I was.

Having been part of a pressure recovery cowl design for a PT-67F I can tell you that what works isn’t intuitive. What works is a reverse funnel shape, that is the opening is the smallest part, what’s intuitive is a funnel, big opening narrowing down to pack the air in.

The reason the reverse funnel works is that your trying to increase pressure, not velocity, and you increase pressure by slowing airflow.

[A64Pilot]

1 hour ago, JayMatt said:

I understand. My question was more around the RAM air Mod than the cowl. I don't need an extra 5-7mph for 13k I can fly a lot of first class direct flights for that. I was just curious if I should consider putting a RAM on or not. 

If it gave you 5-7 mph then it’s likely worth it for a lot of people.

But I don’t think it does, pretty much none of the speed mods do give you what they are supposed to, if they did the a fully modded F would blow the doors off of a J, and I don’t think it will, but then I don’t think there is much difference between an F and a J either.

Personally as much as Mooney valued speed above most other things I can’t imagine them removing the Ram air if there was a significant speed difference and as apparently Lopresti was heavily involved with the J I’d be surprised if it’s ram air was a poor design.

[N201MKTurbo]

If you are not at WOT, there is no benefit to opening the ram air. If not at WOT and you want more MP just push the throttle in.

[201Mooniac]

4 hours ago, mike_elliott said:

very minimal benefits to ram air on a J. The Bennie of the LoPresti is mainly cooling without a speed penalty

Mike I have to disagree here, the factory ram air on my J gave about 1/4" MP increase which was not noticeable in any real sense.  The LoPresti cowling gives me 1.25-1.5" MP increase and that certainly does impact TAS at altitudes where I would be WOT.  Overall on my J, the LoPresti cowl gave about a 7kt increase above 8K', much of that from the MP increase and some from drag reduction.  I had the first one that was installed and have been very happy with it for the past 13 years I think it is.  It is a very expensive mod though (if it is still available) and might not be worth it for most typical J missions.

[JayMatt]

https://www.emapa.aero/Mooney-Cowl-Kit-p/mooney-cowl-kit.htm

Seems they still may exist. 

[A64Pilot]

17 minutes ago, N201MKTurbo said:

If you are not at WOT, there is no benefit to opening the ram air. If not at WOT and you want more MP just push the throttle in.

Define benefit, there is a measurable increase in MP and that’s the discussion. It’s pretty easy to make the argument that increased MP = increased HP, and increased HP = increased speed.

The discussion is by how much.

My bump of .2 GPH of fuel flow assuming mixture remained constant equals 3 HP LOP (.2x15=3) So how much additional speed is 3 HP?

Mooney had the mold etc for the Ram air, if you look at it, it’s not a complicated thing at all, any money savings from deleting it is minimal at best, so Mooney willingly gave up significant speed for minimal $$ savings?

I don’t think so, Mooney deleted it because it didn’t make much difference and did possibly have less than desirable effects if you forgot and left it open by ingesting unfiltered air, but even that’s not much as every carbureted airplane I’ve worked on bypasses the air filter with carb heat on, and your way more likely to have it on when landing and taxi.

[A64Pilot]

47 minutes ago, JayMatt said:

https://www.emapa.aero/Mooney-Cowl-Kit-p/mooney-cowl-kit.htm

Seems they still may exist. 

16K, plus 50 hours install at $100 an hour, $5K then paint. I have no idea on paint, $2K?

So $23,000?

Sell your J and buy a K  

[kris_adams]

at 10k I'd seriously think about it.  I love the look and it appears that the inspection doors are much longer.  I haven't seen one in person and I can't tell from the pic's.  Plus I need paint anyway so that's moot...but 16k plus 5k install...not sure I can get there.  Love it though

[N201MKTurbo]

43 minutes ago, A64Pilot said:

Define benefit, there is a measurable increase in MP and that’s the discussion. It’s pretty easy to make the argument that increased MP = increased HP, and increased HP = increased speed.

The discussion is by how much.

My bump of .2 GPH of fuel flow assuming mixture remained constant equals 3 HP LOP (.2x15=3) So how much additional speed is 3 HP?

Mooney had the mold etc for the Ram air, if you look at it, it’s not a complicated thing at all, any money savings from deleting it is minimal at best, so Mooney willingly gave up significant speed for minimal $$ savings?

I don’t think so, Mooney deleted it because it didn’t make much difference and did possibly have less than desirable effects if you forgot and left it open by ingesting unfiltered air, but even that’s not much as every carbureted airplane I’ve worked on bypasses the air filter with carb heat on, and your way more likely to have it on when landing and taxi.

I don’t think you get my point. Let’s say you want 20 inches of MP, so you set your throttle to 20”. If you open the ram air, now you have 20.5”, so you need to reduce your throttle to get back to 20” There is no point opening the ram air unless you are already at WOT and want more MP. After all, in your original post you said you were at less than full throttle. MP is MP, it doesn’t matter much how you get it. If you open the ram air and reduce the throttle, you are just trading one restriction for another.

If you are saying that it is taking less pumping effort by the engine to get that manifold pressure because of the increased pressure upstream of the throttle plate, yes that is true, but I bet it is unmeasurably small.

[Ragsf15e]

On my F it’s closer to 1”mp and worth ~4 knots at 8000’ ish.  Obviously WOT up there.  I have had maintenance on it before when the control cable came disconnected, so it’s not free.

[1980Mooney]

1 hour ago, JayMatt said:

https://www.emapa.aero/Mooney-Cowl-Kit-p/mooney-cowl-kit.htm

Seems they still may exist. 

 

26 minutes ago, Kris_Adams said:

at 10k I'd seriously think about it.  I love the look and it appears that the inspection doors are much longer.  I haven't seen one in person and I can't tell from the pic's.  Plus I need paint anyway so that's moot...but 16k plus 5k install...not sure I can get there.  Love it though

I think it is vaporware.  EMAPA is Blue Skies Aviation.  They also claim to sell Monroy Extended Tanks. - They take money and don't deliver per past topics.  Ask WAT if they are actually selling any Mooney cowlings.

 

 

[A64Pilot]

16 minutes ago, N201MKTurbo said:

I don’t think you get my point. Let’s say you want 20 inches of MP, so you set your throttle to 20”. If you open the ram air, now you have 20.5”, so you need to reduce your throttle to get back to 20” There is no point opening the ram air unless you are already at WOT and want more MP. After all, in your original post you said you were at less than full throttle. MP is MP, it doesn’t matter much how you get it. If you open the ram air and reduce the throttle, you are just trading one restriction for another.

If you are saying that it is taking less pumping effort by the engine to get that manifold pressure because of the increased pressure upstream of the throttle plate, yes that is true, but I bet it is unmeasurably small.

I don’t believe your understanding what I’m saying.

I’m saying if it’s worth .5” that within reason your getting .5” whether 1/2 throttle or wide open.

But we can accept this as true, either Mooney was stupid for removing it, or they did so because it was of little benefit.

I don’t believe J’s that have it sell for anymore than J’s that don’t, and if they were faster with it, don’t you think there would be a market for installing it on J’s built without it?

A kit to do so could be sold at a profit for just a few grand, yet there is no kit? Not that I know of anyway.