Engine air intake

[4RNB]

Situation: After a different engine was put in my C172M, the air intake and filter was recessed a bit, I recall a couple inches. There is no longer any kind of seal between the cowling and the intake/filter. Is this important? My AP/IA was not concerned. To help, I've attached a photo snipped from youtube from someone else's plane. Note the easy air passage around the filter
assembly.

 

[Magman]

By a “ different engine “ I believe you are referring to a Plains or Penn Yan

180 STC’ d conversion? If so; the Install Instructions should document the changes

in this area. The conversions are not “ just” an engine swap. There may also be

changes to the exhaust, battery mount, air box , etc.


My take is you are correct to have some concern. It’s difficult to tell from this pic

if you do have a problem. IIRC the original “M” air box had a plastic “ flange”

and also black baffle seal.


While you are looking in this area check that the Cowl Bumper is also present.

This is a steel piece near the alternator that accepts the loads from the

Lower Cowl being pushed back by air loads. They often get lost. Maybe someone

will post a pic.

 

[4RNB]

Yes, Airplains upgrade.
I forget what happened with the airbox, but I'd like to get it looking "right".

 

[Magman]

Aesthetics is a minor concern in my book.

Proper pressure differential for effective cooling would motivate my quest.

 

[Bell206]

After a different engine was put in my C172M, the air intake and filter was recessed a bit, I recall a couple inches.

I could be wrong, but I believe on the older 180 kits the original airbox was modified by the STC and reinstalled. The newer kits had a replacement box. Maybe check to see if your air box was modified correctly. A 2-3 inch gap doesn't sound right.

 

[4RNB]

I could be wrong, but I believe on the older 180 kits the original airbox was modified by the STC and reinstalled. The newer kits had a replacement box. Maybe check to see if your air box was modified correctly. A 2-3 inch gap doesn't sound right.

This was last year, so newer kit. Sales agreement said new airbox was included. I forget what the issue was at install but now I am trying to figure out what needs to be done.

 

[4RNB]

Aesthetics is a minor concern in my book.

Proper pressure differential for effective cooling would motivate my quest.

I do not understand this as it applies to my plane.

 

[Bell206]

This was last year, so newer kit. Sales agreement said new airbox was included. I forget what the issue was at install but now I am trying to figure out what needs to be done.

Maybe something was done to the cowl air scoop for the previous install? Also check you have the correct STC airbox for your S/N just to be sure. Maybe call the STC holder for input?

 

[4RNB]

Maybe something was done to the cowl air scoop for the previous install? Also check you have the correct STC airbox for your S/N just to be sure. Maybe call the STC holder for input?

Not sure. I have now convinced myself to make the long drive to see the plane this week. Cowling should be off, gonna make a video of bottom cowling and the air intake. Talk to mechanic if he is around and has time.

 

[Magman]

“ like to get it looking ” “right”. Per #3. (Aesthetics).

If a seal is missing the pressure in the lower cowl will be higher than desired.

Cool air in the upper cowl may not have sufficient pressure differential for

sufficient downward flow through the fins.


If you make the trip assure you have the Installation Instructions.

 

[Dan Thomas]

Proper pressure differential for effective cooling would motivate my quest.

If a seal is missing the pressure in the lower cowl will be higher than desired.

Cool air in the upper cowl may not have sufficient pressure differential for

sufficient downward flow through the fins.

This. Many earlier 172s and 150s didn't have seals around the filter housing, and cooling was compromised. The seals fixed that. But I came across too many airplanes where that seal was shot, or removed by someone that didn't know why it was there. One has to remember that Cessna didn't spend money where they didn't need to.

On the 172, that seal is a plastic thing with rubber strips and costs a million dollars or something. I found a much better STC'd replacement from Dynamic Propeller. They make it of fiberglass, which takes the shaking much better. http://www.dynamicpropeller.com/cessna-172--182-airbox-products.html

 

[NordicDave]

Plus if the engine STC was not installed according to the instructions, then the installation is not airworthy. I don't think anyone has the authority to unilaterally change an STC and call it airworthy without a letter from the STC holder. Usually there is a log entry that ends with something to the effect of "installed as per manufacturer's instructions".

This is POA, someone will make a list of exceptions to the exceptions.

 

[Brad W]

Aesthetics is a minor concern in my book.

Proper pressure differential for effective cooling would motivate my quest.

I personally agree about aesthetics.... if it's not a 'showplane' that you try to take pride in and keep looking nice.....
EXCEPT that it speaks to sloppy workmanship and short cuts taken..... so I'd wonder what else has been shorted or cheated that I can't readily see?

...and just gut intuition but I agree about questioning pressure differentials for cooling
but I'd also wonder if it might affect pressures/flow through the intake filter in some weird way

 

[4RNB]

Thanks everyone.

update

it is the proper air box, just needs the fiberglass baffles. Shop is ordering

Perhaps conversations from aug 22 not well remembered

but in the future the right stuff will look good

 

[Magman]

Pic is a 1974 172 with the Air Plains 180 hp upgrade.

Conversion was done 20ish years ago.

The black strip surrounding the filter housing is a seal although I’m unsure of type.

 

[4RNB]

Pic is a 1974 172 with the Air Plains 180 hp upgrade.

Conversion was done 20ish years ago.

The black strip surrounding the filter housing is a seal although I’m unsure of type.

Do you have an engine monitor? What kind of CHTs/EGTs are you getting at what power settings?

I've just done 8 hours of flying over the past week. Engine has just over 40 hours on it, I'm still running it pretty hard. When I try and do some leaning the old way (set RPM 2400-2500, pull mixture back until RPM drops a bit or roughness detected, then twist mixture in 2-3 times) I am able to get fuel burn to less than 8GPH and speed seems to stay nearly the same. But, my CHTs want to climb above 400, not buy much, not really more than 420, and I get some flashing EGTs (which I want to really just ignore) In order to get my CHTs much below 400 I have to enrichen the mixture back to a fuel burn approaching 10 GPH. I have not tried this much at 2300 RPM yet.

I am hoping that getting the air inlet baffle put on will lower my temps a bit and allow lower fuel consumption.

 

[Magman]

Sorry; not my aircraft.

Owner at Oshkosh.