[83GMCK2500]

Originally Posted by DirtyLarry

Hey Devin,

Cool! Sounds like a fun project. Yeah, the guts probably came loose on your muffler. I had a 2005 Silverado HD that did the same thing…..very annoying. Regarding the cats, if you can get away with replacing the cats with a “test” pipe like I have on my Suburban (wink, wink) you could have whoever is doing the ECM tuning just tune out the rear sensors instead of dummy sensors.

Regarding exhaust pipe size for a BBC, it seems the preferred size is 2.5” where claims of 3” or bigger takes too much back pressure way equaling loss of low end torque and anything smaller is too restrictive. I couldn’t really tell you on velocity/flow characteristics as that seems to be what appeals to each person’s ear but I can tell you that an older BBC, like the Vortec 454 you’re working on, requires a completely different muffler/exhaust configuration than an LS engine or even an 8.1L due to the different firing orders of the newer engines (1-8-7-2-6-5-4-3) compared to the older engines (1-8-4-3-6-5-7-2). The newer firing order engines absoluty need an H, X or x-muffler to sound right, otherwise they wound sounding like two poorly running 4 bangers having a shootout while the older engines like yours sound darn good with true duals, with two individual mufflers. I personally have never had an H or X pipe in an older firing order engine as I always thought they sounded good just plumbed the old school way (twice pipes with two mufflers).

My K10 has true duals, H-pipe and two individual Thrush mufflers (Cheap $30 Flowmaster knock offs). This same exhaust was on the truck when it had a 454 and sounded great but once I swapped in the 8.1L with the different firing order it sounded horrible. Added the H-pipe and now it sounds like a mix between a 60’s muscle car at WOT, cackle of a medium duty truck at low RPM and a Ferrari at cruise. Very weird, but it sounds awesome to my ear. Meanwhile, the Burb’s 8.1L is running a dual inlet/dual outlet Magnaflow X-muffler (can’t remember the exact name and I’m not home to look up the part number) but it sounds great with zero drone found with the typical dual inlet/outlet mufflers. Really quiet idle and cruise but it has a set of LUNGS at WOT almost like there is an exhaust cut out welded in somewhere. The videos posted of my Suburban are not the new Magnaflow exhaust but the old out 2” Flowmaster that sounded great with a 350 but a 50 caliber machine gun spinning at 50,000 RPM’s with an 8.1L. It was horrible. If it were me with an L29 454, I would go with cat “test” pipes and 2 individual Flowmasters or Thrush Flowmaster knock-offs (not a dual inlet/dual outlet muffler). Dual inlet/dual outlet on a 1-8-4-3-6-5-7-2 engine makes way too much interior drone for my liking. Dealt with that on my old ’98 Z71. Not sure if that helps you or adds more to the confusion but that I my offering to your question. I’m sure the heck no exhaust expert. My wife says I'm deaf anyway so my trucks may sound like crap to other people but they sound good to me now

Oh, I almost forgot....I have a Flowmaster dual in/out Big Block Muffler on a '93 C1500 with a 454 and it drones like mad. Sounds good, but the drone at throttle tip in is pretty sucktastic. It sound great on the outside though

Fantastic information, thank you very much. I had a feeling I came to the right forum and the right thread. Experience is invaluable, thank you for sharing yours. I will take your muffler suggestion under advisement as well, will probably be listening to a lot of youtube videos and/or soundclips.