Mufflers 1967 Fb - Vintage Mustang Forums
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post #1 of 11 (permalink) Old 07-24-2019, 05:11 PM Thread Starter
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Mufflers 1967 Fb

Question:
I have a 1967 fb crate 351w 400hp with headers. Are these mufflers loud? The car currently does not run and was just wondering what you guys think? I am not looking for anything crazy loud and obnoxious. And I donít know anything about this style of muffler.

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post #2 of 11 (permalink) Old 07-24-2019, 05:21 PM
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If that's all you have for mufflers, they they will be quite loud. Those are straight-through "glasspack" style mufflers, and pretty small at that, which makes them louder.

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post #3 of 11 (permalink) Old 07-24-2019, 05:41 PM Thread Starter
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Mufflers 1967 Fb

Obnoxious loud?

This might be easier way to judge on how loud?

How loud is this going to be.
10 being crazy obnoxious loud.
1 being normal 1967 289 stock muffler stock engine stock exhaust.

Is this like a 6?

Or like a 9?

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Last edited by rpm2380; 07-24-2019 at 05:47 PM.
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post #4 of 11 (permalink) Old 07-24-2019, 06:29 PM
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Shorty glasspacks like yours, but bolted directly to the headers without pipes would be a 9. Maybe a 10, as they can be just as loud as open headers in the right conditions. If those are toward the back of your car, they probably do help a little, so call 'em a 7.

While very low-restriction (even more so than a straight pipe!), glasspacks are a perforated pipe wrapped in fiberglass, inside a shell. The matting gets full of soot and stops being fluffy over time (or blows out the tailpipe), at which point they tend to be pretty dang loud. Think Thrush and Cherry bombs. Usually, the longer they are, the quieter they are, but no glasspack is going to be mellow and tame sounding. They have a beautiful savage snarl, which changes to explosive cackling as you let off on the gas. Absolutely classic exhaust sound for a musclecar - but often really annoying out on the highway. The quietest glasspacks are probably going to be about a 6-7.

"Turbo mufflers" have a wider body and typically force exhaust to travel in sort of an 'S' pattern inside. They offer a lot more sound deadening, but they're also a bit more restrictive. Magnaflow is an exception to this. They are called "turbo mufflers" but they are more like 'better built' fat glasspack mufflers. They are superior in flow to most Turbo mufflers, but have better sound-deadening than a glasspack muffler. While not 'quiet', these are probably more like a 5-6 on your loudness scale, when combined with a full exhaust.

Lastly, chambered mufflers are pretty common these days. Think "Flowmasters". They come in different lengths, which quiet things down based on size more or less. Bigger = quieter. Your typical Flowmaster 44 sounds like someone lighting off packs of Black Cat firecrackers in a culvert. It is a hollow, boomy, annoying sound. Instead of depending on damping materials and perforated pipes inside, chambered muffles use baffles to help attenuate exhaust pulses. They would rate probably about a 6-8 on the loud scale. Their hoarse, sad, echoing thud attracts droves of millennials and fraternity kids with lots of money but no taste or common sense. (What? No! I'm not biased!)

The classic stock muffler setups are typically a combination of perforated pipes and fiberglass damping inside. Most of them are pretty restrictive.


Edit: OOPS. I was putting a "1" at more like "early 70s luxury car quiet". I'd say a full stock mustang with the resonators and cross flow exhaust would be maybe a 4 on that scale, so adjust my numbers accordingly!
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Last edited by Grimbrand; 07-24-2019 at 06:34 PM.
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post #5 of 11 (permalink) Old 07-24-2019, 06:43 PM Thread Starter
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You obviously know a lot about mufflers. Would you keep these on or swap them out. And if I swapped them out would I have to modify anything?


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post #6 of 11 (permalink) Old 07-24-2019, 06:44 PM
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Glass packs also tend to get louder over time as the fiberglass burns out and then it is just a straight pipe.

1967 Mustang, mild 351W, 750 Demon, MSD, Pertronix, long tubes, Dan williams built top loader with Hurst shifter, #550 coils, 5 leaf mid-eye springs, 3:55's, CSRP disc brakes.
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post #7 of 11 (permalink) Old 07-24-2019, 06:47 PM
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If it was my car, I would try them out for a while. If they're just too flaming loud, maybe consider using them as a resonator and adding a second muffler, or just replace them with some good turbo mufflers perhaps.


Unless you want your car to sound like Gary Busey trying to sing opera while gargling beer, avoid chambered mufflers though. Unless you like that sort of thing.

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post #8 of 11 (permalink) Old 07-24-2019, 07:21 PM
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I recently tried the el cheapo thrush chambered mufflers on my 70. I like them. They are a 4 on loudness at idle. Nice sound on highway. Nothing like flowmaster. It sounds good to my ear, and the price was right at summit. 36 bucks each I think.


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post #9 of 11 (permalink) Old 07-24-2019, 07:27 PM
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Why does it not run? Maybe the best approach is to concentrate on that aspect first, start it, get it tuned and operating properly....then decide on the mufflers. However, I agree with David...probably going to be loud.

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post #10 of 11 (permalink) Old 07-24-2019, 07:52 PM Thread Starter
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Itís a shop doing paint body, 5 speed swap, and a hand full of other items to get her on the road.


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post #11 of 11 (permalink) Old 07-24-2019, 08:08 PM
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Mufflers

Get it on the road with what you have. If you can live with the interior sound you're halfway home. They will get louder if they are Glasspacks.
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