M20J style engine baffle on M20E

[EricJ]

A 337 always requires an IA signature, so if the A&P isn't IA, then it will need an additional signature.    There needs to be approved supporting data,  and you can check with your IA to see what they will require for that.

 

[David Lloyd]

For some good reading on cowling airflow, open baffling versus doghouse, go over to vansairforce.net and search posts made by Dan Horton.  He frequently references research done in the '40s and '50s to explain what is happening inside our cowlings. Van's uses open baffles similar to what the later Mooneys have.  On at least one of Sabermech's cowling installs, he used what appeared to be a standard Van's baffle kit. When Dan Horton built his RV, he went to great pains to build a plenum instead of the standard baffles, plenum being a fancy name for our doghouse.  After many years, much research, many explanations and many changes, Dan wrote that either system is good.  The difference between the two is not the big picture but the small details.  Either done well cools the cylinders and oil.  Either done poorly does neither.

The C never got the open baffles, keeping the doghouse through it's life.  G the same.  The E and F went from the doghouse to open baffles in 1967 as FlyingDude points out.  Many people complain about their doghouse because they are old, vibration has taken it's toll.  I think each one was hand-fit, parts may or may not work without modification.  To get the most from either style, spend some time in a dark hangar with a light to find all the holes in the baffles and seal them tight.

[FlyingDude]

Thanks guys for the great info... I'll do the reading as suggested. If they're equivalent in their cooling capability, I won't insist on doing this mod too much...

[carusoam]

All small steps in the right direction…

If you get too tied up with all of the modifications possible…

You end up spending about 700+amu to get a newer Ovation…

Nothing more enjoyable than having all of your cylinders reading nearly the same chilly CHT… to match the nicely balanced EGTs…

Nothing less enjoyable than having one CHT, and ancient doghouse, in poor condition… and you single EGT isn’t calibrated or have actual temps under the needle…

 

Without a decent engine monitor… you comfortably don’t know what you don’t know….  
 

PP thoughts only, not a mechanic…

Best regards,

-a-

[BobbyH]

Let me see if I can throw some fuel on the fire.  IMHO you can achieve similar results with either the plenum (doghouse) of the baffled compartment.  What you have is a pressure box with exits over the cylinders and out various tubes for cooling and heating.  The fluid dynamics of air is pretty simple, it will quickly go to the path of least resistance.  It's important to make sure your baffles and dividers are tight, not allowing air leaks etc.  The goal, like @carusoam mentioned is efficient and equal cooling on all cylinders. 

One advantage of baffling is that it is much easier to access plugs and ports on top of the engine, no need to dismantle the plenum once to cowl is off. 

An advantage of the plenum is that it is easier to ensure it is sealed properly, you can inspect it right there and see any openings.  FYI, just place a light inside and see where it exits through seams etc. 

A big factor for good cooling is proper use of your cowl flaps.  It's the low pressure side of the flow equation.  Personally I was quite surprised how little my cowl flaps opened in my 'E' model (I'm used to the C-182).  I may need to adjust mine to gain every last bit so that it is pulling the air through the system.  Those cowl flaps actually create a light vacuum due to the venturi affect.

Getting a decent engine monitor is on my shopping list.  My old Super 21 has to wait for this new owner to gain some more AMUs. 

Bob