Tuning Exhaust by heat

My K2500 is used mainly to pull our camper. It has a stock (fresh) vortec 350 with BB tune and dual 3" exhaust. The overall package works very well, and the truck and camper are matched well. I have been trying to make this as quiet as possible without killing the power.

From what I have learned over the years racing atvs & motorcycles (that had to pass sound tests), if you choke the exhaust down too much, it creates excess heat and all paint will be burnt off of the muffler and pipes. So, here I am. I have 2 walker glasspacks that have 20" of baffle + an 18" magnaflow. Dumped before the rear axle.

The pics show that there is paint on about the last 25% of the glasspacks. This tells me that I could add tail pipes (or maybe even combine it into 1 pipe?) that go over the axle and out the back. If I can y it into 1 pipe, that would probably quiet it down a bit more - thinking that if the heat is already out of the exhaust, flowing fast enough isn't an issue?

Any input on my thought process here? This method worked well on small engines, but I haven't messed with cars enough to know if it tranfers over.

Hi, Tuning by heat can work and help when you are dealing with the same engine and the same components over time. This does not necessarily translate to different engines or components. For example just a different brand of paint may change color at a different temperature. I can tell you from prior experience that for the most V8's with 3" exhaust dumped straight out of two mufflers will be pretty loud. Adding a tailpipe to before the tires will quiet it a bit but not alot. I have found that dual three inch tailpipes out over the rear axle and out the back will help quite a bit but still be pretty load. What really helps is a smaller system if you want quiet. For the most part for example a 2.5" dual exhaust set up with 2.5" mufflers & no tailpipes will be about the same noise as a dual 3" exhaust and 3" tailpipes out the back. Maybe not the same tone but on a db meter it will be pretty close. I have more experience with tailpipes on street cars with baffled mufflers not straight core. I do have experience with straitght core mufflers more similar to your glasspacks but I have only used those on a few street cars and on the race cars never with tailpipes. All the street cars I have used glass pack style straight mufflers mostly because of packaging were small cars or trucks with 4 cylinder engines and I ended up with Monza style tips at the back of the car/truck so the engine wasn't too load on the street. I have had Camero's with dual 2.5" Flowmaster mufflers with no tailpipes that were super loud because of big cams and would set off car alarms everytime out and you just put dual 2" tailpipes and the car is very quiet. Not stock car quiet but now you can start the same car at 4 am and not wake up all your neighbors and set off alarms as you go down the street from your house. Single tailpipes seem to help to but I have only used single 3" pipe but its quiet compared to dual 3" pipes which are very load the single 3" pipe really helps out on idle being more quiet. "H" pipes ahead of the mufflers can help a bit too and that is where I have heard you should install the "H" pipe where the paint stops but have never dyno tested different locations as I just install them whre there is space lol. Also I have noticed a difference in loadness between 2.5" non mandrel exhaust and 2.5" all mandrel bent exhaust as you would get from Flowmaster for example. The 2.5 mandral is loader than a 2.5 non mandral exhaust probably cause the bends are more restrictive and thus quiets the exhaust a ton. I would guess 2 1/4 mandral tailpipes are about the same loadness as 2.5" non mandral bent pipes. Probably why the 2" non mandral exhaust pipes on a Camaro were so much quieter in the example above! Kind of a long reply but hope this helps!

Exhaust systems are tuned primarily by pressure pulses, not by heat content--although temperature does affect the pressure pulse tuning by changing the speed of sound.
If I remember correctly, hot gasses have a higher speed of sound.

There's guys still repeating the hoary old myth about using a tire crayon, or some random spray-paint on the exhaust tubing and telling folks to put the H- or X-pipe where the paint stops burning.

So what's the deal with your exhaust? Removed the catalysts, and installed glasspacks?

If that's a factory-original muffler, you need to shitcan it ASAP. You'll probably find that it's necked-down internally from the inlet and outlet pipe sizes. At least, they are on the OEM 7.4L mufflers in '97.

Yes, tailpipe(s) will quiet the noise in-cab substantially.