# Does Muffler Length Make a Difference?



## Sdpepper (Jun 3, 2021)

I'm replacing my Flowmaster mufflers for the quieter Dynomax Turbos. The Dynomax come in two different lengths--14 inches and 20 inches. My Flowmasters are 17 inches. I have room to go with the longer case length so wonder if it is better to go with the 20 incher or go with the shorter Dynomax Turbos if length doesn't make a difference? My exhaust pipes are 2.5 inches. Any advice would be appreciated in advance.


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## Jetzster (Jan 18, 2020)

Depends on how loud you like it!
The older I get the deeper lower sound the better😎 I’d get the 20s if they fit ok but that’s me,
runnin HP-2s , the 409SS ones at 18”
prob Dynomax 20s give you a throatier lower rumble


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## O52 (Jan 27, 2019)

I had 20s on my SS El Camino. Fairly Quiet at low engine speeds. Then they really came alive above 2700 RPM.


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## Sdpepper (Jun 3, 2021)

Jetzster said:


> Depends on how loud you like it!
> The older I get the deeper lower sound the better😎 I’d get the 20s if they fit ok but that’s me,
> runnin HP-2s , the 409SS ones at 18”
> prob Dynomax 20s give you a throatier lower rumble


Thanks Jetzster! So, longer case is quieter than shorter?


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## Jetzster (Jan 18, 2020)

Oh yeah, moocho quieter😎
might be on utube somewheres 
most are


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## Sdpepper (Jun 3, 2021)

O52 said:


> I had 20s on my SS El Camino. Fairly Quiet at low engine speeds. Then they really came alive above 2700 RPM.





O52 said:


> I had 20s on my SS El Camino. Fairly Quiet at low engine speeds. Then they really came alive above 2700 RPM.


Thanks 052. At my age I’m leaning toward a quieter sound but a nice throaty sound if I step on it.


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## PontiacJim (Dec 29, 2012)

Sdpepper said:


> I'm replacing my Flowmaster mufflers for the quieter Dynomax Turbos. The Dynomax come in two different lengths--14 inches and 20 inches. My Flowmasters are 17 inches. I have room to go with the longer case length so wonder if it is better to go with the 20 incher or go with the shorter Dynomax Turbos if length doesn't make a difference? My exhaust pipes are 2.5 inches. Any advice would be appreciated in advance.


Add an exhaust cross-over pipe which seems to be a way to quiet the exhaust down. This enables the use of both pipes/mufflers to help quiet things.


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## Sdpepper (Jun 3, 2021)

PontiacJim said:


> Add an exhaust cross-over pipe which seems to be a way to quiet the exhaust down. This enables the use of both pipes/mufflers to help quiet things.


Hi Jim. Yes, my 67 has an H pipe but the Flowmasters are simply too loud for my taste. What are your thoughts on changing them out for Dynomax Turbo 20’s?


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## Baaad65 (Aug 29, 2019)

I have 2.5 Pypes Race Pro 14" long w/crossover and love the sound, not to loud until you open it up and no droning 👍


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## PontiacJim (Dec 29, 2012)

Sdpepper said:


> Hi Jim. Yes, my 67 has an H pipe but the Flowmasters are simply too loud for my taste. What are your thoughts on changing them out for Dynomax Turbo 20’s?


On my '68 Lemans, I just had a slightly warmed over 400CI and ran 3" pipes, no cross-over, to Dynamax mufflers to the rear axle and then turn-downs, no tail pipes. This was about 15 years ago as I recall, but the issue with Dynomax at that time was that the created a resonance/drone around 2,500 RPM's, Below that or above that and it was gone. That drone was supposedly fixed by Dynomax. I like it as I would purposely hold my car in 2nd gear at 2,500 RPM's ans cruise down out main boulevard - everybody heard me coming and heads were turning, and why I like loud pipes.

I don't recall the length, but I still have them and plan on using them on the 455 in my Lemans when I get car rebuild #2 all together. I have Doug's headers and again, will run 3" straight pipe off them to the Dynomax.

Another thing many say is that you want to have the tail pipes exit past the rear bumper for a little more quiet. Back in my youth, it was always the Corvair Turbo mufflers we all ran - they were short, and sounded deep & throaty and made enough noise. 

I think you may want to listen to a few sounds of muffler types on YouTube. They may not be exact as each car is different, but it can give you an idea of the sound.


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## armyadarkness (Dec 7, 2020)

I wish that I could get my car loud! I have Dougs headers, 2.5 stainless, mandrel bent pipes, no crossover, and Flowmaster 40's. The car is SOOOOOOOOOOOOOOOOOOOOO quiet. I'd do turndowns at the axle, but Im afraid of the corrosive exhaust all over the underside of the car.

Yes, the crossover really quiets the exhaust down. Especially the X style.


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## gtojoe68 (Jan 4, 2019)

PontiacJim said:


> On my '68 Lemans, I just had a slightly warmed over 400CI and ran 3" pipes, no cross-over, to Dynamax mufflers to the rear axle and then turn-downs, no tail pipes. This was about 15 years ago as I recall, but the issue with Dynomax at that time was that the created a resonance/drone around 2,500 RPM's, Below that or above that and it was gone. That drone was supposedly fixed by Dynomax. I like it as I would purposely hold my car in 2nd gear at 2,500 RPM's ans cruise down out main boulevard - everybody heard me coming and heads were turning, and why I like loud pipes.
> 
> I don't recall the length, but I still have them and plan on using them on the 455 in my Lemans when I get car rebuild #2 all together. I have Doug's headers and again, will run 3" straight pipe off them to the Dynomax.
> 
> ...


I have the old Dynomax 20’s, RamAirResto factory cast iron headers (d port heads) with an X crossover and straight chrome tips out back. Nice and low grumble at idle, fairly mellow tone when cruising and that loud resonance drone PJ mentioned right at 2100. When you hit it WOT, she really sings loud. You can still hear the QJet secondaries though sucking the equivalent of one human’s annual oxygen too, which I love hearing. But I do have a ragtop so I don’t want it too loud as to drive me out of the car. I like them and recommend


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## Sick467 (Oct 29, 2019)

I have a new set of Dynomax 20’s on a mild 400 build (72 Cheby Truck with 300 to 350 hp with exhaust manifolds and 2-1/4" dual pipes). It is nice and quiet at an idle and really doesn't get very throaty even at higher RPM's. I do like some noise upon opening the secondaries ...so, I flipped my air cleaner lid over to give a 3/8" gap and now I get some intake sounds out of it under full throttle. That's good enough for my low HP truck, but I really want my 67 GTO to sound like it should. I, too, get the drone at 2-2500 RPM with the truck. I will be considering larger pipe diameters, HO exhaust mani's, and the shorter Dynomax Turbo's, when the time comes for the GTO. My only concern is that the GTO motor will be built to be around 400 to 450 HP and that alone may drive the sound levels up to where the 20" mufflers sound "right". Time will tell and that will be a fair piece off as the full restoration starts this year and mufflers will be a long ways off. This thread has me wondering what length unknown turbos are under it now. I'll check. I really like the sound now.


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## GTORAD (Jun 21, 2015)

Sdpepper said:


> I'm replacing my Flowmaster mufflers for the quieter Dynomax Turbos. The Dynomax come in two different lengths--14 inches and 20 inches. My Flowmasters are 17 inches. I have room to go with the longer case length so wonder if it is better to go with the 20 incher or go with the shorter Dynomax Turbos if length doesn't make a difference? My exhaust pipes are 2.5 inches. Any advice would be appreciated in advance.


Yep the longer case will definitely be quieter.


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## Rockinindian (Aug 5, 2021)

Sdpepper said:


> I'm replacing my Flowmaster mufflers for the quieter Dynomax Turbos. The Dynomax come in two different lengths--14 inches and 20 inches. My Flowmasters are 17 inches. I have room to go with the longer case length so wonder if it is better to go with the 20 incher or go with the shorter Dynomax Turbos if length doesn't make a difference? My exhaust pipes are 2.5 inches. Any advice would be appreciated in advance.


I have headers on the 389/421 heads P4B edelbrock I use "old skool" 40" glasspacks. Great sound not too loud but gives it a HEALTHY sound and zero restriction.


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## coyote595 (Dec 4, 2019)

I just put on a Pypes 2.5" dual exhaust system with no crossover. I used the new Pypes Turbo Pro mufflers. I am very pleased. Low deep mellow tone and gets louder when you step on it. No drone on my car. Good for a mature guy like me (60 years old). I have the pipes going all the way back to the rear bumper. I did not want anything really loud. Wanted to be able to talk in the car without yelling.


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## Khmike (Jun 21, 2021)

Rockinindian said:


> I have headers on the 389/421 heads P4B edelbrock I use "old skool" 40" glasspacks. Great sound not too loud but gives it a HEALTHY sound and zero restriction.


It's a mixed bag to be sure, I love the sound of my current set-up: Old School Cherry Bombs (with likely zero internal material). When I really open it up, it sounds like it's ready to rip something into pieces and I'm sure I can be heard for a 1 mile in any direction. I was thinking of going to Flowmasters to quiet it down when I enter and exit my neighborhood! I think I'll take PJ's advice and try to find Dynomax output samples online first.


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