J3 Exhaust

[JimC]

I've attached a PDF of a potential exhaust mod for J3's with -12, -12F, and O-200 engines.

It allows the use of unmodified A-65 collectors, muffler shroud, and tailpipe, and eliminates the need to trim the lower cowl.

The muffler is omitted, and the end tubes have offset entry to accept the stock headers (which lowers the shroud enough to clear the oil screen housing). The exhaust is radiused from the stock headers to the stock tailpipe in order to improve flow and power.

Carb heat and cabin heat outlts are retained, though not shown in this preliminsry drawing.
Cabin heat efficiency is somewhat reduced due to the lack of a muffler.
Any thoughts or comments?

 

[Grant]

Jim,
I have a 90-12 and would be interested. Are you going to make these? I like the idea and have yet to tackle the exhaust on my project.

 

[JimC]

No plans to make it, except maybe a couple for myself. If you want me too, I'll add the cabin heat shroud outlet to the drawing, and you are welcome to give it a shot. If you do, let me know how well it works for you.

 

[marcusofcotton]

I'd expect some slight improvement, would be great to see valid before/after testing. Amazing how often basic flow principles seem to be over looked in various systems.

 

[bob turner]

I keep reading that there is a problem with the stock engine exhaust system when a dash 12 is installed. We have two Cubs with dash 12 engines, stock muffler and shroud, stock cowls, and a mere 1/8"extension on the rear stacks, easily done with an extra "no-blow" steel gasket. Granted, there is a small dent in the muff for cleaning the oil screen, but since we have to inspect the muffler every 50 hours anyway, there isn't even a need for that.

What are we doing wrong?

 

[JimC]

Marcus, that's true. Although fluid mechanics is my area of interest, my primary focus here was just maintaining a near-stock esthetic for the -12 engine installations. Increased efficiency was secondary.

Bob, I've done it that way too. I don't see anything wrong with it, but have seen some folks object to the dent and the double gasket.

 

[willyb]

Pretty much the 0-200 Legend set-up.

Bill

 

[JimC]

I wonder if the Legend setup would fit the 3?
Does Legend use the stock J3 stacks?
If not, will it fit the stock J3 stacks?
With the muffler omitted, is the Legend system very loud?

Edit - Why does Legend require the addition of an Alternator with their exhaust system?
"Lightweight 30-Amp alternator must be used".

 

[Super11XP]

Here are some pics of the one we build for legend. If this is too much like advertising please disregard and delete.

 

[bob turner]

Inartful use of words? As in " you cannot use a larger alternator"?

Clint has a jig that adds an eighth of an inch to the rear stack when he replaces the flanges. Easy. Do you clean your screen more often than every 50 hours? In fifty years, all I get out of that screen is little bits of carbon.

 

[Wannabe]

I keep reading that there is a problem with the stock engine exhaust system when a dash 12 is installed. We have two Cubs with dash 12 engines, stock muffler and shroud, stock cowls, and a mere 1/8"extension on the rear stacks, easily done with an extra "no-blow" steel gasket. Granted, there is a small dent in the muff for cleaning the oil screen, but since we have to inspect the muffler every 50 hours anyway, there isn't even a need for that.

What are we doing wrong?

Mine is the same way.

 

[JimC]

Bob, that's all I ever get out of them too.

Clint, thanks for the photos. No resemblance to the J3 exhaust (as I'm sure you know).

Would you be interested in building a one-off crossover per the attached preliminary drawing?
(the final drawing would have considerably more dimensions, and they might vary slightly from this drawing)

If interested, do you have an idea of what the approximate cost might be?

 

[Super11XP]

pm sent.

Bob, that's all I ever get out of them too.

Clint, thanks for the photos. No resemblance to the J3 exhaust (as I'm sure you know).

Would you be interested in building a one-off crossover per the attached preliminary drawing?
(the final drawing would have considerably more dimensions, and they might vary slightly from this drawing)

If interested, do you have an idea of what the approximate cost might be?

 

[cubdriver2]

Here are some pics of the one we build for legend. If this is too much like advertising please disregard and delete.

Would be cool if someone built that " Y " setup that fit between stock manifolds

Glenn

 

[JimC]

Glenn, look at my 'Y' CrossOver PDF. It fits between stock J3 A-65 manifolds, clears the -12 oil screen housing, and uses the stock muffler shroud.