[Lifetime Goat]

I purchased the Pypes H 2.5 in system in 2004 which came with Dynomax Turbo mufflers hooked up to RAIII manifolds. System sounds great above 3000 rpm but when I am just cruising between 1500 and 2500 rpm the sound is awful.
Is this just the way it is and if so are there any good choices to replace these for a quieter sound?

[tom s]

Im on my 3rd set of mufflers on my 69 bird.I think im going to try the factory type with small resonators under the car and the Xflo in front of the gas tank.At 2000 i have 84 decibels in the drivers seat.I really think my best set was the Hushpowers made by Flomaster,Super Turbos were the worst and the stock type supposed to be quiet are not much better.Was worse with a X pipe than a H pipe.Tom

[ZeGermanHam]

In addition to playing around with different muffler setups, you might also consider installing some Dynamat (or similar) sound deadener on your floor pan underneath the carpeting. That might help keep the sound waves from vibrating through the body shell and into the cabin.

[Scarebird]

IIRC I ran a pair of these, seemed to work with crossflow exhaust.

https://www.summitracing.com/parts/jex-jr25

[burd]

Borla

[76TA462]

I had to go to Borla (Pro XS Series) for ground clearance. I used my existing Pypes cross X. This resulted in droning I didn't have with my Ultra Flo Welded mufflers. I added Vibrant Performance Resonators 1793 just after my headers and that worked for me.

[JLMounce]

H pipes have a propensity for drone, especially with straight through style mufflers. A rule of thumb I learned from my late model mustang days was that this combination generally mattered.

With an H-pipe, run a chambered muffler like a Flowmaster
With an X-pipe run a straight through muffler like a Magnaflow

I have the Pypes 2.5" system with X-pipe. Originally I had the Violator mufflers and there wasn't any drone in this system but it was just very loud everywhere. I replaced the Violator mufflers with a set of Magnaflows. The car is now pretty quiet while cruising around in the city, or even on the highway, until you get into the throttle, then it wakes up nicely. There's absolutely no drone anywhere.

If you're not currently doing so, make sure you are running full tail pipes as well. Dumped mufflers will create a higher propensity for drone as well.

[78w72]

you will get all kinds of suggestions on what mufflers sound good or dont have drone as you can see by the above posts & other threads on this over the years.... but every car or engine combo is different & every persons opinion of good sound or level of drone is different.

so its kind of hit or miss going off all these suggestions, one guy will say dynomax super turbos are the best & dont have drone, while others say they were the worst for drone (myself included) or the very detailed suggestion of "borla" with no info on what model# or the rest of the exhaust system, then the very next post says borla resulted in drone compared to ultra flows....

but i will throw in my suggestion based on results of 4 different pontiac engine 2nd gen firebirds ive built/own, flowmaster 40 are the worst for drone but some like that sound & they do sound pretty good overall on a mild 400 with 2.5" H pipe crush bent full length pipes, drone was much worse before adding full tail pipes. had super turbos on a mild built 455 with headers & 2.5" crush bent pipes, drone was horrible but didnt have full tail pipes.
the least drone but loudest is pypes race pro, which are a straight through design like ultra flows, on a 500+hp engine with big 2" headers, x pipe & 3" full length mandrel bent. its not exactly "quiet" with that set up of course but the drone is very minimal compared to other cars ive had or friends cars ive ridden in.


consider an X pipe, they are said to reduce the noise/drone a lot but increase power, they also change or lower the idle sound & cam lope sound.

[Lifetime Goat]

So one suggestion I have heard is that for the same style muffler get one that is longer and that will lessen the sound over the shorter muffler (14" vs 18") Is there any truth to the claim that a longer muffler of the exact same construction will be quieter?

[JLMounce]

Depends on the construction. If it's an absorption style muffler, the longer case will make the car quieter. Typically this does reduce drone as well, but not always. Drone is a resonant frequency and when it occurs it's because the exhaust pulses traveling through the pipes and into the muffler are bouncing around in a chaotic way that cancels some frequencies and amplifies others. Because of this, going to a longer muffler may not always eliminate drone, though you can almost be assured that it will at least lesson it. Of course the trade-off is that the car will be quieter everywhere.

This is why an X pipe works so well to calm down drone, it focuses the exhaust pulses and smooths them out. The trade-off of course being that you typically lose some of the lope from your cam and it has a tendency to create a higher pitched note than some people prefer on their classic muscle cars.

A chambered muffler is a whole different animal. It has tuned length runs that force the exhaust pulses to bounce in a specific way to attenuate frequencies and cancel others through an audio process known as phasing. It's what gives chambered mufflers their characteristic sound. Because there's no actual absorption of sound, going to a different sized case doesn't always mean a reduction in sound level or drone.

[tom s]

In my ordeal I have not found X pipes better than a H in my 69 bird.Tom

[JLMounce]

Tom have you tried adapting a Pro Chamber? I don't think anybody makes these for classics, but there's a lot of Mustang guys that swear by them. Especially the SN95 mustangs suffer horribly from drone issues.

It produces a deeper tone more like an H pipe, but because it's effectively a helmholtz chamber, it turns whatever headers or manifolds you have in front of it into something more akin to a 180 degree header.

[78w72]

Originally Posted by tom s

In my ordeal I have not found X pipes better than a H in my 69 bird.Tom

not better at what? sound/drone or performance?

[Formulajones]

One thing people always seem to miss is the hanger system. It has such an affect as to how that sound is transmitted throughout the car, and I haven't found a better hanger system than what the OEM used.

These exhaust system kits come with some of the most rigid hangers that have very little absorption ability and any resonance that the exhaust makes can be exaggerated throughout the car.

First thing I do is toss the hangers and buy a complete factory style hanger kit from your favorite classic car parts supplier. I find these hangers have more of a free hang design that does allow the system a bit of movement, but most importantly less likely to transmit noise.

From there it'll come down to pipe and muffler choice. I tend to like "X" cross overs better, as they seem to control drone and low rpm sound better than an "H". I also prefer the larger 20" Dynomax Ultraflow mufflers but not all cars here have that.

There is a mixture here of Dynomax Ultraflow, Pypes Race Pro in both a cross flow muffler and a dual muffler setup, The GTO with an older set of tiny Race Mufflers that only measure 12" in length and have nothing inside them, Some of these cars are 3 1/2" systems, 3" systems, and a few with 2 1/2" systems. None of these cars exhibit any hint of drone at all. They all have "X" cross overs. They all use factory style hangers.

I can go on a rant with a full page of stuff I've tried in the past with several types of Flowmaster, Spintech, Magnaflow, MAC, and some I've probably forgotten over the last 30 years. I have had the Dynomax Turbo mufflers the OP mentions, if they are the same thing I'm referring to. One of the first sets of mufflers I ever had on my Chevelle back in the 80's, and those have got to be some of the quietest mufflers I've ever used, close to stockish sound with the stock pinch weld appearance and not a straight through design, packed with all kinds of sound absorbing material. I can't even imagine how you've been able to make those drone.

One thing for sure, these Pontiac RA exhaust manifolds don't help the cause. I've been back and forth with headers and RA manifolds on my own Firebird and for sure the headers have a much quieter and smoother sound. The RA manifolds increased the raspy sound as they don't scavenge as well, but drone can still be controlled with them.

Lots of suggestions here, take your pick what you want to try.

[Lifetime Goat]

I did not think about the hangers but you are absolutely correct about the sound transmission. Thanks.

[tom s]

I can give a tinker damn about performance on my street driving cars!The drone at my cruising RPMs is a deal breaker for me.I know I can put lower gears and drive at 300 RPMs higher and it goes away.Too pig headed to do that!Tom

[Formulajones]

I prefer performance AND and quiet and comfortable ride.

Just takes a little more effort to get it there.

I used to be all performance, but as we get older, I still have the fast bug, but now I want to do it in a more comfortable manor.

My opinion dad's 700hp GTO is one of the most comfortable A-bodies I've ever driven and ridden in. Smooth, quiet, cruises at 75 at 2300 rpm and even knocks down respectable mileage all things considered.

My Chevelle is a close second. If it had ride quality like the GTO I'd say it's a wash.

[rohrt]

I fought the drone blues in my 68. It had 2.5 X pipe setup. Started with a strait through spin tech mufflers that came with the system. Moved to ST 14" chambered mufflers. Finally went to VT mufflers to fix my issue.

In all the research I did almost any combination can have drone and almost any change might cure it.

[Entropy11]

I think there is some truly insightful yet often overlooked info in this thread so far.

I agree with FormulaJ that the hanger system plays a huge role with drone and/or the reduction of it. Adding fixed/rigid points on an essentially “floating” system is a problem waiting to happen. Factory hangers often appear over-engineered but there’s a reason for it.

Before getting into a costly exhaust swap I’d start there. Even if you do get into swapping parts later, you will have a great foundation for it. I forget who I got my factory hangers through… I’ll have to look it up.

[6869GTO]

See you have a vert. Is the noise worse with the top up compared to top down?