Turbo muffler internal design
 

I think all turbo mufflers have two 180 degree turns. Some have turning vanes to help direct the flow. Do the vanes realy help?

My project: '64 Lemans Sport Cpe., GTO Option, stockish 389 CI, Tri-Power, RA exh, manifolds, 2.5" pipes.

From reading previous posts I've decided to run Dynomax 17749s, which I think have the turning vanes. A year out from being road worthy, so I picked up a pair of inexpensive Jegs turbo mufflers to use on the run stand a discovered they have no turning vanes. Just curious if the vanes help with anything other than flow.

Garden variety “turbo” mufflers will hinder power, Jim Hand showed that years ago…recently the Steves and Dave showed it on an episode of engine masters.

The turbo muffler’s appeal is sound, with performance taking a bit of a hit.

Dynomax super turbos are a different breed, they have flow directors, and as such kinda sorta a little bit act like straight through mufflers. The 17749 that you’re looking at did really really well in Jim Hand’s testing.

Walker/Dynomax also makes a traditional style turbo muffler, I believe it’s under the Dynomax banner, but not referred to as a Super Turbo. The number escapes me.

Aside from the functional internal differences, its case is an inch or so narrower than the 17749/47, which could benefit A body owners with big rear control arm braces. * shrug *

Like money pits mentioned, there are garden variety turbo mufflers that are much like you described.
Dynomax is a bit of a different breed and known for their excellent flow characteristics while providing good sound that isn't overly loud. Most of their designs that I'm familiar with are a straight through design and use a packing material to dampen noise.
There are a few other mufflers that have copied the design and flow similar.

There is some variation on the internal design of the Dynomax Superturbos dependent on the case size. I have the smaller 16" 17629 model, and it has a totally different design, without the flow directors that most people think of when discussing superturbo mufflers. They just have the dimples in the outer case (see photo attached).

Although I have Dynomax superturbos currently installed on my car, I think the Summit Racing turbo muffler is a better choice. I also own a pair of those (not installed), and they are better constructed (in the US), cheaper, and don't neck down to 2-1/4" internally like the Dynomax Superturbos do.

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Resurrecting this partly because I'm also in the hunt for some turbo mufflers for the '65 Lamnas.

Unfortunately, I don't want the reduction in diameter on the internals either...but the Summit Racing ones you mention actually DO neck down...at least for the 3" ones...

Summit Racing™ Turbo Mufflers
Made with free-flowing large diameter tubing—as much as 20 percent more than some competitors—Summit Racing™ Turbo mufflers offer you deep performance tone without being too loud. They feature 2.5 in. internal cores with 360 degree perforations, roll-seamed end caps, 100 percent aluminized construction, and seam locked cores that prevent the center baffles from twisting out. Installation is a breeze with their fully reversible design. The mufflers are available in a variety of inlet/outlet diameters and locations. Order the model that best fits your application.

The nice thing about the Dynomax Super Turbos, P/N 17770, is that they maintained the 3" on the inside, but I think they've been long discontinued...

FWIW Summit uses this same description on all of their USA made turbo mufflers, even the 2 1/4”.

First, I’m not an engineer, but retired from the HVAC trade. A sheet metal journeyman told me to increase airflow velocity, the duct size would be decreased then oversized similar to a thumb restricting water from a garden hose. Not sure if this applies to mufflers or crimping down is a production cost savings.?.

Yeah, I was referring to the 2.5" units that do not neck down internally.

There are 2 case sizes for the Dynomax Super turbos. The larger case (5.5 x 11") with 3" inlet and outlet do not neck down internally. The smaller case (4.25 x 9.75) do neck down for the 3". I believe the 2.5" in/out maintain the same size regardless

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You're 100% correct...I actually discovered that after my post and ordered the 17792s. They arrived today.