Muffler recommendations
 

Just had a new exhaust installed on the firebird and don't like the sound, too loud and it just drones. I wanted something a little louder than stock but now I want something quiet. Any recommendations? Its a 69 firebird with a 350 manual trans and stock exhaust manifolds.

Dynomax Super Turbos - No drone, very efficient and would fit your desire for a "little louder than stock".

I agree with above answer. Just wondered what’s on it now?

I have Dynomax Super Turbos that I am planning to put on my car because I want it to not be loud, but I'm surprised to hear folks saying they are efficient and don't hurt power too much. There have been episodes of Engine Masters which show the turbo style mufflers were significantly restrictive and down on power compared to chambered style mufflers. Agree that if you just want something for a cruiser that is a little louder than stock, turbo style mufflers are a great option. But I'd stop short of calling them efficient.

Also FWIW, the 2.5" Dynomax Super Turbo mufflers actually neck down to 2.25" inside, but the Summit brand turbo mufflers are a true 2.5" all the way through.

-The straight-through mufflers with packing (flow piping doesn't do 180* turn) flow the best.
-Turbo mufflers where the exhaust has to 180* and back again, are less efficient.
-Chambered mufflers vary a lot by manufacturer design. They rarely, if ever work as well as straight through. But comparing to turbo-style some are occasionally marginally better, many often worse.

Turbo mufflers were installed, not sure of the make.

As far as the Dynomax recommendation, what you want for quiet is the 17749 long case super turbos. I have regular 14" ones on my Catalina now and will be switching up soon after riding in a friend's 64 Catalina with the long case ones. He has a Len Williams 455, 041 cam, Rhoads lifters and long tubes. Exhaust is 3" with H pipe to the mufflers and 2.5" tailpipes out the back. The car is damn near silent inside even cruising at 3k rpm.

I have a 78 T/A with a complete RAIII and RAIII manifolds. In the 80's my car would blow exhaust manifold gaskets constantly. I tried every kind of gasket to no avail. I always thought I needed to bring the manifolds to a machine shop to have them cut. I came across a set of Flow Master two chamber mufflers and put them on. I never blew another manifold gasket again, its been 40 years. Point is, Turbo mufflers not as free flowing as one would think.

Jim and Tom Hand would dispute your claims. Per their extensive testing on Jim's '71 Le Mans 455 powered wagon, the Dynomax 17749 had one of the lowest backpressure ratings, the lowest sound level, the fastest speed in the 1/4 mile, and the 2nd quickest time of all the tested mufflers.

https://www.pontiacstreetperformance...p/exhaust.html

https://www.pontiacstreetperformance...ix/exhaus1.jpg

https://www.pontiacstreetperformance...ix/exhaus2.jpg

https://www.pontiacstreetperformance...ix/exhaus3.jpg

https://www.pontiacstreetperformance...ix/exhaus4.jpg

Love my Borlas, straight through, but not loud. Million mile warranty too.

It also had the largest body, which is also a factor. But if you compare similar sizes like the 17734 and Cyclone Turbo, the straight-through Borla did better in backpressure and 1/4 mile ET.

The chambered flowmasters were all on the low end of performance. Supertrapps are kind of their own animal since they're essentially a tunable tailpipe. Not sure what the AP Xlerator or discontined CVX muffler designs were like inside.

I put 17749s on my brother's 1970 LeMans vert with a 530 Hp motor and 4 speed. Was going to go with the Dynomax Ultraflows, but it would have been too loud with the top down. The 17749s are perfect sound wise and no drone. I used a Pypes 2.5" mandrel bent system and 2" headers.

With a Torque Tech mandrel bent, with band clamps that didn’t bent the pipes, I didn’t like how Pipes puts their Logo on stuff, you can’t remove it easily, and they were very thin tips at that.
The ones I saw at a show were out of round they were so thin. I had a custom 2.5” set made.

amcmike

I run the 17749's on the GTO. Why look at anything less efficient and/or more expensive - regardless of brand name?

Besides, it's what the OP poster is looking for.

The 20” case 17749 is my go to for both of my ‘64 A-body Pontiacs, however they’re simply too long to fit in the recess under the back seat floor pan of an F-body.

I used a pair of the 14” case 17734 mufflers on my ‘76 T/A and they were a good fit, I suspect your ‘69 has similar space constraints. They were a little more aggressive sounding than the larger 17749 mufflers but still good for something you’re driving a lot. Smaller 2-1/4” tail pipes would tone them down a bit without sacrificing performance.

Ground clearance with dual exhaust and these fairly large mufflers isn’t that great. If a low profile muffler with good sound quality is available I’d be looking into those. There just isn’t much room under the floors of an F-body.

I think one of the tests I saw the TV guys do they were stunned at how well the Super Turbos actually flowed. Not sure they had done lot of studying to see how the flow directors work but likely as not, they did not have time nor desire to advertise one brand over another. They were learning that the front pipe diameter is more important than muffler style, assuming the mufflers are close in flow capability.

On an early Bird, I'd go with a free er flowing crossflow muffler due to ground clearance. Today, I would check with Waldrons for just such a mellow soundling free flowing crossflow mufler. Years ago under my '68 400 Bird convert, I sourced a walker dynomax crossflow w 2 1/4" inlet/outlets (was originally spec'ed for a Buick GN). Worked well but engine was not a max effort 400 build.

Have used numerous pairs of DynoMax 17747's & 17749's under A-body's, & have more 17749's to install on own A-bodys. Both of those part numbers are the longer 20" case, but are fairly thick & under an F-body, unless ones into the Bootlegger look, or the cheap springs/ 4WD look, ground clearance is limited.

As far as Jim & Tom Hand's EXCELLENT exhaust comparison articles, one also has to understand that research is near 25 years old, there are several comparable 2.5" inlet/outlet high flow mufflers avail today which provide excellent flow & sound quality & are of slightly smaller case design & of lighter weight.

One not mentioned is spin tech. Can’t speak to back pressure but they sound pretty good and don’t have any drone. That’s what RARE suggested for my system.

There was a statement about efficiency of turbo style being less than chambered (which I believe the opposite to be true most of the time). I simply categorized the 3 main types so there was no confusion, and then how they typically perform relative to each other.

Then you said the Hands data contradicted my general statements, and I pointed out how they actually supported my statements. The brand names I used in my follow up post was simply to identify and relate back to the performance of the test, to show my original statement was valid. I never implied one brand was better than another. Nor did I say there's anything wrong with Dynomax or that turbos don't flow well.

I didn't realize we weren't allowed to correct information, support our statements, nor add technical content beyond an OP's original question.

The most interesting thing about Jim & Tom’s testing was that they used a single exhaust setup to get that much performance difference out of them.

Oh, I might add that their CD is still more all time favorite music c! ��

I can't say the source of the data, but there's this floating around the internet. https://www.forabodiesonly.com/mopar...pg.1715284008/

That is some of our data as well Mike. :):). Substitute Magnaflow for the Straightline Performance data. This is data that shipped with the CDs.
The early Spin Techs were pretty loud.

Thanks for all the replies, it helps a lot.

JMHO!83 decibel at 2200 is not acceptable for me.Tom

How were the dB measurements in that spreadsheet taken? Are those dB numbers from an engine dyno? Or inside a car with full interior? Full-length exhaust tubing? Headers?

Here is how we did it. This is the sheet we included with the CD back then. Background was controlled to the point that we got accurate measurements. We repeated the recording and testing if anything was out of place or different.
Tom Hand

Thank you for purchasing “Silent Power, the CD”.

Before you buy exhaust components, we know you would like to hear what they sound like. The sound depends upon the engine and the type of modifications done to it and the type and size of muffler and pipes used. What sounds one way on a Ford or Chevrolet may not be representative of what it sounds like on a Pontiac. Now, because of the generosity of many, this CD of Muffler sounds is possible.

We would like to share a few details about the engine, the mufflers, the exhaust system, and the recording configuration.

The engine is a 1975, 455 cubic inch Pontiac with 7K3 heads, a cast iron intake, a 750 Quadrajet, an HEI ignition, a Pontiac Ram Air Four camshaft, and three-tube aluminum coated headers.

Seventeen popular 2 1/2” inlet and outlet mufflers to fit GM A-body cars, like GTOs and Chevelles, were selected. Some of the mufflers also fit Firebirds and Camaros. Four 3” mufflers that also fit A-bodies were selected. Specifically for the Firebirds and Camaros, four cross-flow mufflers were chosen. Three of these had 2 1/2” inlet and outlet bushings and one had 2 ¼” inlet and outlet diameter bushings. Additionally, two OEM replacement mufflers were used as “references”. One is the true “Turbo-Muffler” and it is from the 1965 turbocharged Corvair. The other is a long body, aftermarket replacement muffler to fit big-bodied Pontiacs.

The engine was mounted on a fully instrumented test stand. Attached to the engine was either a pair of 3” front exhaust pipes or a Dr. Gas 3” X-crossover equipped system. Reducers were used to allow the 2 1/2” mufflers to fit on the 3” front systems. When 2 1/2” mufflers were attached, mandrel bent 2 1/2” tailpipes were used. When the 3” mufflers were being run, 3” mandrel bent tailpipes were used. For the cross-flows, special adapter pipes were made to let them fit the front systems. For crossflow tailpipes, Dynomax supplied mandrel bent, 2 1/2” Firebird tailpipes.

The microphones and sound level meter were located ten feet from the tailpipe outlet. Sound levels were measured at 750, 2200, and 3500 RPMs. Even though the sound level may sound similar on the CD, refer to the data sheets for the actual measured sound levels. On the data sheet, you will also find suggested (2001) retail prices for the mufflers, their physical dimensions, and flow ratings of them relative to open pipes of the same length and diameter as the mufflers.

We hope this CD proves useful for your future exhaust purchases.

Tom, you guys are Hands down awesome! :-) Thanks.

The Hand family has been a literal fountain of knowledge in the Pontiac world. Thanks Tom for providing this info to those of us still following in your dad's giant footsteps in making quick Pontiacs with a combination of affordable parts and diligant attention to detail.

So would it be safe to assume that the dB levels listed in the table above would be considerably lower when measured inside the cabin of a car versus 10 feet behind the tailpipes? Of course it would depend on the car, how much interior sound deadening was in it, etc.

With regard to Tom S's comment above and acceptable dB levels, I interpret the readings above to mean that 83dB at 2200rpm (for example) is not what you'd actually experience when driving the vehicle. Those are tailpipe measurements.

Tom, any plans for updated testing? Many new options since the "Silent Power" production, yet very little accurate/reliable testing data out there since then.

The testing you and your father have performed over the years is VERY highly regarded and appreciated by many of us.

On my 1968 Firebird I have Flowmaster Delta Flow 50's. These are 3-chambered with a thicker long case to help minimize drone. Here is an older video before I had the car restored:

https://youtu.be/LB1y6jtuKlU

I had heard and read so many good things about the Dynomax large case mufflers that I had settled on a pair for my 62 Catalina. Unfortunately, they are not available in the large case, double offset inlet/outlet. I searched every brand I could think of and NONE of the common manufacturers made this case design except for the AP Xlerator stainless case mufflers. I was skeptical but ordered a pair because the size was correct. They were also reasonably priced for a stainless steel muffler. Much to my surprise after installing them yesterday and driving around for 100 miles, I really like these mufflers. System is 2.5" front to rear and it is a tight fit. Car is quiet at cruise, not raspy under power like almost all chambered mufflers and deep/throaty/but muffled at idle. Engine dyno'd just under 500 HP, solid lifter cam, 251/259 duration @.050. Idle 1000 RPM. I recommend these for street use if you don't want a really loud/raspy exhaust note.

Here are a few pics from the shop where I had the system made. I have since dressed the ends of the tailpipes and removed the stickers. This was my first time using this small old school shop. I have over the past 30+ years only used two shops. Both of them unfortunately, have either closed or the guys who were real craftsmen, have retired. This little place, called the Exhaust Warehouse in Fairborn, OH did a nice careful job and made sure everything was symmetrical and fit. He made the over the axle pipes in 3 pieces to avoid crushing them. The entire system is welded, end to end, which looks great but will be hard to deal with if repairs are needed. PM me if you want more info about the shop and could use their services. System was a super tight fit for such a huge car. Head pipes over the crossmember as stock. Very close fit to the driveshaft, very close to the speedo cable on the right and shift linkage on the left. Close everywhere over the axle to the control arms and shocks. Clears everywhere. No idea why the p;ictures are turned or how to fix them. Help?

Maybe it's an optical illusion, but the passenger side off the exhaust manifold on top looks crushed or kinked.

I see the area your looking at, I think. It looks much like the driver side which you can see better. It's where the pipe is clamped and stretched making that tight bend. Yes it is mis-shapped a little. Probably lose 1/4" effective diameter. Not allot of options there. It is not crushed. If you or someone else can turn the pics, that would be greatly appreciated. I just don't know how to do it on this forum.

It appears to be crush-bent tubing, which I'd imagine is typical of what most small exhaust shops would do. You can see similar (though less pronounced) indentations just behind the mufflers and right where the tailpipes turn down before terminating. Not the end of the world.

https://i.imgur.com/eNeRsbA.jpg?1
https://i.imgur.com/EmkhhjS.jpg?1
https://i.imgur.com/QDfxN72.jpg?1

First, thank you for turning the pictures! Yes the pipes begin as 10' straight pipe sections. A typical exhaust pipe bender holds the pipe in a fixed position and a movable die stretches the tube using hydraulic pressure. A bender in good condition can make a 45-60 degree bend without kinking it and retain a smooth path inside the pipe. More than that, you get an inside protrusion, (kink). A typical shop or pre-bent pipes from a supplier generally don't care and the pipes are kinked internally. This gentleman, Todd, was willing to use some mandrel bent pieces I provided to get over the axle, and weld them in 3 pieces to fit properly with no kinked tubes. Is it perfect?, no. It is also mild steel vs stainless which is even harder to bend without kinking. It also cost about 1/3 of what a full mandrel bent, stainless system would have cost. I couldn't find anyone in a 100 mile radius willing to build a complete welded mandrel bent stainless system for ANY price. Pretty happy with this for an occasional use street car.

I am curious how loading affects the sound measurements. I expect the exhaust system of an unloaded engine running at constant rpm to be quieter than when accelerating.

How do these "quiet" mufflers compare when accelerating? Do some get "relatively" louder than others?

My car has glass-packs that were welded in when I bought it. If I get it running and driving, they will have to go so I'm curious. I would like it to be quiet until I wanted it to be noisy...

I've had experience with Flowmaster Delta 40's and Super 40's on my 2016 Challenger SRT392. Both mufflers had similar "quietness" at idle. But cruise, part throttle, heavy throttle and WOT were different between them. The Delta 40's cancelled out drone at cruise and part throttle acceleration, but was TOO quiet at heavy and WOT. Completely took away the car's personality. Inevitably I switched to the Super 40's. I could hear the exhaust at cruise but still without any droning. And under heavy or wide open throttle the exhaust had a deep throaty rumble.

The difference between the two products was that the Delta 40's had a smaller case and more baffles within. Whereas the Super 40 had a larger case made with thicker metal and less baffles.

The decibel level of the muffler will be influenced by the amount of noise cancellation factored into its design.

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I’m looking at muffler options for my 70 TA. I’ve heard these Black Widow Venom 250’s on Autotopia and they sound great. Very unique sound. Has there been any outside testing on them? It’s similar to a spintech or flowmaster since it’s chambered.

I’m considering the Venom 250 in 3”. My current engine makes around 660hp. Next year when it’s turbo’d it will be in the neighborhood of 1200hp-1300hp

https://youtu.be/NPhCFPeLTjQ

https://blackwidowexhaust.com/mufflers/

http://lstwo.com/images/87631215066687298581.jpeg

It seems everyone is calling the 17749’s a very quiet option. Is it like factory quiet, or does it have a little rumble? I’m wanting someone that is slightly above factory noise to at least let you know you have some motor.

If that’s what you’re looking for in a muffler they’re the right ones for you.

Just replaced my Flowmasters with a pair of Borlas . The sound is just right...inside and out

what about a walker 18293

No, they are not factory quiet. Louder, but not obnoxious

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19 inch Flowmasters .....let it RIP

I've had the same 17749's (with an H-pipe) on my GTO now for about 20 years. Able to hold a conversation quiet inside the car and a nice rumble outside. With no other changes but the mufflers, I went from Flowmaster 50 series and an incredible drone inside the car to Dynomax 17749's and no drone or resonance.

Spintech for the win. Can get them made as long, thin case, and/or wide as you can fit, "stuffed" inside if you want as well to knock down sound. Great muffler.

I have Flowmaster 40s that aren't for everyone. They're loud...but I'm loving the exhaust note/tone. Very aggressive, but at 55 mph (3.23) with windows down we were able to easily talk. Might get a little old over time... we'll see. It's always been part of the musclecar experience for me.

I need to record it.