Classic Chambered Exhaust Classic Chambered Exhaust Inc

PO Box 426 - Highland, MI. 48357 - (248) 889-4364

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Cobra Muffler Retrofit

Here is the procedure to install the inlet “funnels” – part # 3530-AD.
One end of the adapter is 3.5” OD, the other end is 3” OD.

Showing inlet end of Cobrapack & new adapter

Cut off the 3” muffler inlet & cut adapter
close at the 3” end

File all burrs off muffler & adapter

Butt-weld adapter to muffler

Cut-off excess 3.5” diameter adapter – leave it a little big for further trimming/grinding as this will just barely fit inside of the merge collector 3.5” OD end: (all you are using is the flare area)

Photo showing the adapters trimmed – nice smooth transitions into the muffler flowpaths. All of this will hide inside the collectors & your collectors weld to the muffler body. This eliminates severe turbulence caused when stock type mufflers are welded to the collectors. Stock mufflers usually have internal cores / flowpaths of less than 2” diameter. Combine tiny cores along with sloppy transitions into the mufflers & this makes for really inefficient & restrictive exhaust. You will lose major HP & Torque because of this – small block or big block applications!

These photos show the 3-pieces that make a “re-do” of a Cobra sidepipe muffler. The 3.5” OD turndown fits over the 3” ID muffler neck – the muffler neck can be trimmed off or left on. You can re-use your turndowns, or purchase new ones from us. They can be trimmed to shorten the overall length or the turndown area of the spout. Our turndowns are mandrel-bent, 16-gauge aluminized steel. They can be ceramic coated or painted. They are made in the USA, like all of the products we produce.

January 2011 - what a cool way to usher in the new year (literally)! A rare occasion, I visited John B's house in the metro Detroit area to personally assist him with retrofitting a pair of 3" x 24" packed COBRAPACK Mufflers on his beautiful 514 CID dual quad Factory Five Cobra. I brought the welder, the chop saw, some of the rest of the tools - John supplied me with assistance & a cold beer at the end! This was the perfect opportunity to document just how easy it is to retrofit a Cobra exhaust - there's nothing to be afraid of as you'll see.

Step 1: After unbolting both sides from the headers, one of the original sidepipes is on the table & ready for surgery:

Step 2: Cut-off & save the bracket tabs - these will be re-welded to the new COBRAPACK Mufflers:

Step 3: Bracket removed with help of chop-saw. Now chopping apart the muffler from the merge collector next to the original weld (this was tough to cut through - you'll see why in the next photo):

Look what the exhaust was running into upon entering the mufflers! Can you say restriction?? The outer wall is 3.5" OD. There was NO smooth transition here - just a very abrubt perimiter causing TONS of turbulence.

Looking into the stock muffler - around 2" flowpath core diameter. OUCH!

Looking inside the 3" core COBRAPACKS with the small funnel cones butt-welded to the inlet. Compare the don't need to be a rocket scientist to know which one will flow better! The funnels will slip inside of the 3.5" collectors, so you will not see them.

Step 4: After chopping the merge collectors apart from the original mufflers, clean up all the steel flash with a grinder or file - inside & out. Get all the paint or ceramic coating removed so you have clean steel to weld to. (John's sidepipes were ceramic coated - clean-up was easy though):

Looking upstream into the merge collector - why restrict it at the muffler after this clean flowpath? There's no need to lose horsepower because of a poor design.

Step 5: Chopping the 3.5" to 3" reducer (part # 3530-AD) at the 3.5" end. The 3" end was already cut down & butt-welded to the muffler at the inlet end at my shop. This is going to create a nice smooth transition from the 3.5" collector into the COBRAPACK 3" flowpath - like a funnel. No turbulence allowed in this new setup!

The end funnel has been chopped again & ground-down so it just slips snugly inside the 3.5" collector. This will all hide inside the collector:

Step 6: John bolts the merge collectors back to the headers. Everything will be positioned on the car before any welding happens. John wanted to improve the alignment & fit anyway, so here was the perfect opportunity:

Step 7: Position everything to check out the new setup. Bolt the little tab we cut off the muffler earlier to the frame bracket, position it to the new mufflers, & trace with a marker. Remove the muffler & weld the tab into place on each muffler. (There is some play in this bracket assembly since it is isolated from the chassis via rubber isolators).

Step 8: Position & weld the tab to the new muffler:

Driver's side all tacked together:

John checks the angle of the turnout (72.5 degrees) to match the driver's side. Let's weld 'er up! (Note the marks made on the turnout & muffler for alignment)

Passenger side all tacked together. Looking good! After this, John will remove both sides & take them to a welding shop where they will professionally TIG weld all the seams with precision. Then, the assemblies will be ceramic coated & ready for final assembly. This took us 3 hours to complete without an air compressor. Not a bad job for a cold Saturday afternoon in the garage!

by astglenn,


Classic Chambered Exhaust Inc. · P.O. Box 426 · Highland, MI. 48357
(248) 889-HEMI (4364) · E-Mail