Performance Muffler Swap

This 1966 Nova SS had a nice dual exhaust system with the exception of a pair of blown-out mufflers. Rather than junk the entire system, we decided to install a new set of Flowmaster mufflers.
This 1966 Nova SS had a nice dual exhaust system with the exception of a pair of blown-out
Check out the look of our superstar muffler installation. It’s not perfect, but it’s tucked-up, secure, and leak-free. The Flowmaster mufflers gave the car a tough new sound and probably released a few extra horsepower. We went with Flowmaster’s two-chamber mufflers (PN 925414) featuring the "side in, center out" exhaust pipe routing configuration. Flowmaster mufflers are constructed of aluminized steel to prevent rusting and have internal metal baffles that won’t blow out years from now.
Check out the look of our superstar muffler installation. It’s not perfect, but it
Begin the swap work by supporting the rear of the car off the ground with a pair of jackstands. In our application we noticed that just in front of the mufflers were small bends with flanges that presented a problem when considering the overall length of the new mufflers. If your car has straight pipes entering the mufflers, the swap will likely be much easier.
Begin the swap work by supporting the rear of the car off the ground with a pair of jackst

To prevent radically hacking and splicing the current dual exhaust system, we carefully measured the existing mufflers and found a close match within the Flowmaster line. As luck would have it, we found a pair of 2-1/2-inch-inlet/outlet Flowmasters with a similar case length and width as the old ones.
To prevent radically hacking and splicing the current dual exhaust system, we carefully me
We cut off the old mufflers as close to the original outlet as possible to leave us more of the original exhaust tubing to work with. It’s a lot easier to cut off more later than it is to try to add more!
We cut off the old mufflers as close to the original outlet as possible to leave us more o
We ran into a problem: The supposed 2-1/2-inch exhaust system, wasn’t. After further measuring, the pipes leading into the mufflers were 2-1/2-inch, the mufflers were 2-1/2-inch, but the pipes traversing over the rear axle were 2-1/4-inch. Doh! To remedy this problem with our current 2-1/2 inlet/outlet Flowmasters, we applied a bit of creativity. We knew that trying to compress the Flowmaster’s 2-1/2-inch outlet to the 2-1/4-inch tailpipes wouldn’t work, so we used a hacksaw to cut slats on two sides of the new muffler’s outlets. Later, as the muffler clamps are tightened, the muffler’s outlet should compress onto the smaller pipe without major leaks--hopefully!
We ran into a problem: The supposed 2-1/2-inch exhaust system, wasn’t. After further

Your arms will need to be in good shape because there’s plenty of laying-on-your-back, under-car hacksawing to be done. After the muffler outlets are cut off, hacksaw the pipe where it attaches to the old muffler’s inlet. It’s helpful to have a buddy hold the muffler(s) as you hacksaw to prevent them from jiggling every time you apply some muscle to cut.
Your arms will need to be in good shape because there’s plenty of laying-on-your-back
Because the existing exhaust system and the new Flowmaster mufflers both had 2-1/2-inch pipe diameters (sometimes new mufflers have a slightly expanded inlet/outlet to allow them to slip onto the old pipes), we got creative in making our own slip-fit connector. First we used a file to slim down the exhaust tubing’s outside diameter, then we filed down the inside diameter of the muffler inlet.
Because the existing exhaust system and the new Flowmaster mufflers both had 2-1/2-inch pi
After some filing to make our own custom slip-fit connection, we wedged the new Flowmaster muffler onto the existing exhaust system.
After some filing to make our own custom slip-fit connection, we wedged the new Flowmaster

Using a 2-1/2-inch exhaust clamp from a local parts store, we clamped the muffler’s inlet to the existing exhaust system.
Using a 2-1/2-inch exhaust clamp from a local parts store, we clamped the muffler’s i
A new 2-1/2-inch exhaust clamp was added to the muffler’s outlet, and then a ratchet (with a 9/16-inch socket) was used to compress the 2-1/2-inch outlet to the existing 2-1/4-inch tailpipe. Sure, the work is somewhat butch, but thanks to our clever notchwork we were able to obtain decent clamping with a leak-free seal.
A new 2-1/2-inch exhaust clamp was added to the muffler’s outlet, and then a ratchet
If you don’t prefer the clamp-it method, or if you’ve got a small exhaust leak after clamping, you may consider welding the connections. We used our entry-level Lincoln MIG PAK 10 wire-feed welder (see "Welding Basics," Aug. 1998) to weld the connections for a stronger, completely leak-free installation. If you don’t have a welder, muffler shops we talked to said they’d do the work for about $20-30. CC
If you don’t prefer the clamp-it method, or if you’ve got a small exhaust leak a

Most gearheads have probably already upgraded their muscle machines with a set of headers and a good dual exhaust system. After a few years, it's not uncommon for the mufflers to wear out (get crunched, rot out, or blow out the baffling), but what if the rest of the exhaust system is still in pretty decent shape? Such was the case with a '66 Chevy II Nova that frequents the Car Craft offices. Rather than install a completly new (and often costly) exhaust system, the goal was to just swap on a set of new aftermarket mufflers at home. Sure, the final look may not be as professional as what a muffler shop may do, but you'll save a few bucks and have pride in saying you did it yourself!