Lots of little last minute considerations before I order a custom tune and start this beast up. . .

I installed ceramic-coated Pacesetter shorty headers and the Jeg's offroad Y-pipe (which now comes in stainless, and they sell it for the same price as the original aluminized one, so I got the stainless one -part number 555-31021). As there is now no cat, I know it will be louder. If I replace the stock muffler with a good flowing straight-through muffler (Borla Pro-XS 40065), it will make the best power and efficiency possible from the single exhaust, but will it be so obnoxiously loud that I would be better off just keeping the stock muffler? Both options are going to be loud, but will there be a big difference between the two?

 

Various dyno tests have shown that unless you buy a super cheap muffler, it have very little impact on power. Get one that will give you the sound you want, don't worry about anything else.

 

True, but those dyno tests were done on systems that were essentially stock. The stock exhaust has multiple restriction points (manifolds are restrictive to flow compared to tubular headers, stock y-pipe with crush bends were restrictive due to very small internal diameter in the bends, can-of-beads style catalytic converter is extremely restrictive, and the large internal volume baffle style muffler causes turbulence and allows for expansion, both of which cause restriction).

If you have a series of restrictions, and you remove any one restriction, you will see little change to the system because the other restrictions each serve to limit flow to a specific rate. But remove most of them and one little change can make a big difference.

At any rate, this is the "equation" I'm trying to solve right now, lol.

 

Without a cat wont you get a CEL and possibly issues with the truck running??

 

Non-fouler trick will work on the rear O2 sensor. Solves the issue.

 

Good to know

 

Watch this. Great example of "bad mufflers" vs "good". Focus on sound and go from there though.

 

How is the quality and fit of that stainless off-road y pipe? I was planning on ordering it for my truck since the cat is gutted anyways and mine is beginning to rot out.

For our trucks I really think you guys are getting too worried about the performance aspects of mufflers. Really anything is better than stock and our trucks don't make enough power that performance baffled or straight through mufflers are going to make enough of a difference that you'll be able to notice it. Find one that you like the way it sounds and run with it.

 

lol this is the case on pretty much any vehicle

 

dapepper9 -Great video. David Vizard wrote the book on exhaust design science and if you read his work, you'll know even more about exhaust science than the guys in that video. I wrote a brief comparison of straight-through vs baffle-chamber mufflers a couple days ago on the "Thinking about getting flowmaster 10 muffler" thread.

97ramrod1500 -I was impressed with the quality of JEGS' stainless offroad Y. It bolted right up to my Pacesetter shorties (which are supposed to bolt right up to the stock catted y-pipe), so it should bolt up to the stock manifold just fine. The only issue is that it is a little short on the downstream end. It just barely slides into the female end of the downstream exhaust pipe. I'd like it to be about 3/4" longer.

Both -On a stock or mildly modified 2nd gen gasser, you're right, muffler choice isn't going to make a big difference in power. If you don't get rid of the multiple other choke points in the stock exhaust, you'd be lucky to make an additional 2% power from a straight through muffler over a baffle chamber (which on a 245 HP 5.9 is about 4.9 HP). However, if you do get rid of all the other choke points in the exhaust, the muffler itself may yield an additional 5% which is only 12 HP, but you'd also gain a little horsepower from removal of each of the other choke points -for example, switching from stock manifolds to 1.5" pacesetter shorties on a stock engine are good for 36 lb.ft @ 2100 rpm and 25 HP @ 4400 rpm. It all adds up. So on a stock engine with stock exhaust, muffler choice won't make a real difference. On a heavily modified engine like mine, which should have around 475 HP and 550 lb./ft. torque, and with an exhaust system that has had all the choke points removed, muffler choice can make a very big difference.

But I wasn't trying to figure out what is going to work the best when I started this thread. I was trying to figure out if a straight-through muffler with a catless y-pipe and headers on a high compression engine is going to be pleasantly loud or if everyone else on the road is going to hate me, lol!