CJ7 with AMC 360 Muffler Choices - JeepForum.com
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post #1 of 24 Old 08-13-2020, 07:32 AM Thread Starter
scottyDive
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CJ7 with AMC 360 Muffler Choices

My wifes 84 CJ7 is getting a stock AMC 360. She is pretty sensitive to sound and we are going to do 2.25 dual exhausts exiting out the back. Anyone have any experience with a good muffler that is mild in sound? We drive this jeep with top off and no doors.


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post #2 of 24 Old 08-13-2020, 07:39 AM
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Magnaflow Quiet series, Walker Quiet Flow are a couple worth looking into. FYI both companies make loud mufflers as well, be careful!
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post #3 of 24 Old 08-13-2020, 08:06 AM
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If you aren't looking for any added "performance", then any stock style muffler will work, especially with duals. Have your muffler shop recommend one.
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post #4 of 24 Old 08-13-2020, 06:02 PM Thread Starter
scottyDive
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I will start researching your suggestions! I heard The Thrush Super Turbo was a good choice. Anyone have these?

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post #5 of 24 Old 08-13-2020, 08:06 PM
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With exhaust out the back and a pair of turbo mufflers it will be fine.
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post #6 of 24 Old 08-14-2020, 06:02 AM
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If you're going to run duals inside the frame, a crossover goes a long way towards reducing sound. It'll pull quite a bit of snap out of even the snottiest of mufflers.


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post #7 of 24 Old 08-14-2020, 06:26 AM
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Originally Posted by Shawn Watson View Post
If you're going to run duals inside the frame, a crossover goes a long way towards reducing sound. It'll pull quite a bit of snap out of even the snottiest of mufflers.


Shawn
Shawn how does that work and about how much is there to gain in doing that?


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post #8 of 24 Old 08-14-2020, 07:01 AM
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Shawn how does that work and about how much is there to gain in doing that?
To be honest, I don't know why it works. Maybe sound waves traveling down the pipe get split up basically doubling muffler volume for dampening. I really don't know. I've personally experienced it several times and it's not, "yeah, I think I can tell"; it's ,"wow, that much?"

As for performance gains, it depends on how restrictive the mufflers are. As those uneven pulses travel down each pipe, if the muffler on that side stacks up as two cylinders hit it at once, the crossover allows any backpressure passage over to the other side but it's not a given that you'll notice much if you have decent mufflers for your hp.

As for sound reduction though, it seems to work 100% of the time.


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post #9 of 24 Old 08-14-2020, 02:46 PM
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Quote:
Originally Posted by scottyDive View Post
.... we are going to do 2.25 dual exhausts exiting out the back...We drive this jeep with top off and no doors.
By out the back you mean out the side corner? If you mean straight back it will draw fumes into the passenger compartment.
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post #10 of 24 Old 08-14-2020, 03:00 PM Thread Starter
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Side corner....the fumes are wicked and I won't have it!

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post #11 of 24 Old 08-14-2020, 06:53 PM
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Quote:
Originally Posted by Shawn Watson View Post
To be honest, I don't know why it works. Maybe sound waves traveling down the pipe get split up basically doubling muffler volume for dampening. I really don't know. I've personally experienced it several times and it's not, "yeah, I think I can tell"; it's ,"wow, that much?"

As for performance gains, it depends on how restrictive the mufflers are. As those uneven pulses travel down each pipe, if the muffler on that side stacks up as two cylinders hit it at once, the crossover allows any backpressure passage over to the other side but it's not a given that you'll notice much if you have decent mufflers for your hp.

As for sound reduction though, it seems to work 100% of the time.


Shawn
Thanks Shawn. Mine is a little louder than I wanted so this might be a good fix.
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post #12 of 24 Old 08-14-2020, 08:04 PM
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Originally Posted by Jim1611 View Post
Shawn how does that work and about how much is there to gain in doing that?
Our American V8s are what we call unbalanced firing motors, but thats also what gives it the unique sound of a muscle V8. So the exhaust pulses are not traveling down the pipes in equal degrees from each other. So looking at the AMC 360 firing order you can see that the same bank sometimes fires twice in a rotation where as a lot of our Euro brothers design their engines to always fire opposite banks.

What happens is the exhaust pulses pressure builds up in one side more so than the other and it swaps back and forth. With two exhaust pulse pushing down the same line the noise cancellation of the muffler decreases. The cross over allows the second pulse of the unequal fire to shift to the exhaust side with the lower pressure allowing the muffler to do its job.

The location of the crossover/H pipe is never going to be perfect as the collision point changes with RPM, tube size and exhaust arrangement. What we used to do in the old days was run the vehicle to cruising RPM, then take some cheap spray paint and paint the pipes, where it bubbled the most was where it was having the collision and we put the crossover there. Today we can use an IR gun to do the same.
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post #13 of 24 Old 08-15-2020, 07:11 AM
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Using bubbling paint to find standing waves for a crossover point is a really good idea but do you get any standing waves downstream of exhaust manifolds?


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post #14 of 24 Old 08-15-2020, 08:18 AM
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Quote:
Originally Posted by Dryseals View Post
Our American V8s are what we call unbalanced firing motors, but thats also what gives it the unique sound of a muscle V8. So the exhaust pulses are not traveling down the pipes in equal degrees from each other. So looking at the AMC 360 firing order you can see that the same bank sometimes fires twice in a rotation where as a lot of our Euro brothers design their engines to always fire opposite banks.

What happens is the exhaust pulses pressure builds up in one side more so than the other and it swaps back and forth. With two exhaust pulse pushing down the same line the noise cancellation of the muffler decreases. The cross over allows the second pulse of the unequal fire to shift to the exhaust side with the lower pressure allowing the muffler to do its job.

The location of the crossover/H pipe is never going to be perfect as the collision point changes with RPM, tube size and exhaust arrangement. What we used to do in the old days was run the vehicle to cruising RPM, then take some cheap spray paint and paint the pipes, where it bubbled the most was where it was having the collision and we put the crossover there. Today we can use an IR gun to do the same.
I learn something new every day, thanks!


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post #15 of 24 Old 08-15-2020, 08:47 AM
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Quote:
Originally Posted by Jim1611 View Post
I learn something new every day, thanks!
Thatís why the 4/7 3/2 swap is popular with engine builders. There is power to be had by changing the firing order, among other benefits. Ford used it on the 351, so itís not like itís a new idea.

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