New Vetterman Exhaust Muffler Output

I have a question for those of you who have the newest Vetterman muffler exhaust (RV-7A, horizontal induction, IO-360), or those of you with exhaust expertise.

After talking with Larry and letting him know I am from Minnesota, he suggested that I have 2 mufflers. I recently installed the exhaust system (went on very nicely) and my question concerns the output of the mufflers. As I see it, I have 3 options:

1. Route the output of the first muffler to the input of the second, then the out put of the second to the heat box on the firewall.
2. Route the outuput of both mufflers to a "Y", essentially combining their output, then route the remaining leg of the "Y" to the heat box on the firewall.
3. Install a 2nd heat box (and control) and route the output of each muffler to its own dedicated heat box.

Is there a correct answer? A wrong answer? Benefits/disadvantages to each?

I put a "Y" in just aft of the #3 cylinder. One output of the "Y" goes to each mufflers input. The right side muffler is my air heater and then the output from that muffler goes to the heater valve on the firewall. Plenty of heat, so no need to collect double the amount for the cabin heat. The left side muffler just dumps out under the cowling.

I think if I were to do it over, I would skip the mufflers. They cost more, are heavier, create more heat under the cowling, the ducting takes up more room, and they are much tighter fit under the bottom of the cowl. I really can't hear a difference in the sound output, and with some decent noise canceling headsets, it isn't loud at all with or without the mufflers.

Lots of photos from my installation here.

Hi Rich,

I have dual mufflers on my 7A with an IO-360 Angle Valve engine. I only have heater (SCAT connections) provisions on the right side muffler. I'm in a warmer climate and think that should be plenty. If its not too big of deal you might just call and get a heat shield for one side and tube up one side only. It'd be easier at least. With my angle valve injected engine, there is not a lot of room in cowl and another SCAT tube would just eat up more volume in the lower cowl. I prefer simplicity whenever it is possible. Less opportunities for failure in the future.

#3

#3...install second heat muff.
Here is the problem. At least for me. Most of my RV flying is VFR and most VFR are days with the sun out. With the sun baking the canopy and one heat muff it is nice and warm in the cockpit. Now...when flying on a trip, say, and flying under an overcast, with no sun, I can see my breath with only one heat muff. So the second heat muff was installed on the left side.

Tip: the 2 inch scat is some standard as the muffs are 2" and the control boxes are 2" but if you read "robbins" notes he says smaller scat or a baffle can be installed to move less volume or slow it down to pickup more heat.
So I used reducers and a 1" scat for easier routing clearance. Works great.

Also in MN and knew from the start I'd build in two heat muffs.

I didn't use Van's heater boxes; rather, I used a slide valve from Tom Berge which vents the outlets from the heat muffs into the cabin. I also routed the scat such that the cool intake air is on the aft end of the heat muff while the warm air outlet is towards the engine side; this cross flow approach maximizes heat output in theory. I'm sure there are other approaches that work as well; this is the one I built.

That, plus some cockpit sealing, means I can fly and be comfortable under an overcast or at night down to about 10 degrees F and on a sunny day down to about -5 degrees F.

macrafic said:

As I see it, I have 3 options:

1. Route the output of the first muffler to the input of the second, then the out put of the second to the heat box on the firewall.
2. Route the outuput of both mufflers to a "Y", essentially combining their output, then route the remaining leg of the "Y" to the heat box on the firewall.
3. Install a 2nd heat box (and control) and route the output of each muffler to its own dedicated heat box.

Is there a correct answer? A wrong answer? Benefits/disadvantages to each?

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I am also in MN and have installed a Vetterman exhaust with dual mufflers in a 7. Since the original post is 4 years old are there any new opinions or observations? I am leaning towards option 3 but with limited firewall real estate can't find a good way to mount the 2nd heat box. Any new ideas?

I’ve been flying my RV7A in Canada for 5 years now including winter. The coldest was when it was -10Celsius (14f) at sea level. I have dual Vetterman exhaust but only using one heat muff feeding one heater box through the firewall. I have found this to be more than adequate. I don’t think I’ve ever used it on full. I do have the cockpit well insulated too.

BTW, Mufflers need some cooling air and the cowl needs protection from their heat. So what I did was cut the unused heat muff in half lengthwise to remove the two fittings that the flex hose connect to. Then mount the remaining portion on the lower side of the muffler as a heat shield for the cowl yet allowing relatively cool air coming down from the cylinders to get to and cool the mufflers. The mufflers should last longer this way.

Bevan

Bevan said:

I’ve been flying my RV7A in Canada for 5 years now including winter. The coldest was when it was -10Celsius (14f) at sea level. I have dual Vetterman exhaust but only using one heat muff feeding one heater box through the firewall. I have found this to be more than adequate. I don’t think I’ve ever used it on full. I do have the cockpit well insulated too.

BTW, Mufflers need some cooling air and the cowl needs protection from their heat. So what I did was cut the unused heat muff in half lengthwise to remove the two fittings that the flex hose connect to. Then mount the remaining portion on the lower side of the muffler as a heat shield for the cowl yet allowing relatively cool air coming down from the cylinders to get to and cool the mufflers. The mufflers should last longer this way.

Bevan

Click to expand...

Interesting. Would you have any pics of your set up?

Jetmart said:

Interesting. Would you have any pics of your set up?

Click to expand...

Not really any useful pictures as it’s a very busy space. Here’s an old photo showing the right side with UN modified heat muff in use. The left side has the two ports cut off and the remainder mounted in about the same orientation.