My new exhaust system

I just finished up my new exhaust system for my 2016. I liked the design of another system that utilized equal length tubes but wanted to create my own using 2.5" tubing and a big muffler. I used Summit Racing's house brand muffler that appears to be very similar to Borla's ProXS 24" muffler. Other than the 409 stainless X-pipe, the rest of the system, including muffler, is 304 stainless. I could not find any 2-bolt flanges in stainless and I didn't want to cut up the stock exhaust system, so I designed some flanges in CAD and sent them off to get machined in 304 stainless as well. They turned out beautifully. One side has a chamfered recessed like the stock flange for the gasket while the other side has a lip to help the welding process.



I measured the driver's side pipe with a string on center so I could get the passenger side loop as close to the same length as possible.



mocked up:



I don't have a backpurge setup but the backside of all weld areas were prepped with SolarFlux B. That stuff worked great to eliminate sugering. Started some welding:



I built my own bender based on "The Machete" design to create some hangers out of 3/8" 304 stainless rod and that worked great.



nearly finished:





ready to install:











It sounds really good and has increased power and torque. The truck holds 6th gear with the TC locked at 55 MPH on a couple hills that it would previously downshift to 5th on. It's much louder on cold starts and has lots of drone between 1.8K-2K RPM, but once it's warmed up, there is very little drone and is really quiet under normal driving. It sounds awesome accelerating through the gears, definitely brings a smile to my face. It is quieter than stock while cruising around town and just a tad louder than stock on the highway/interstate. 4K+ RPM feels more useable now when previously the engine felt flat and out of breath. I'm an amateur at tig welding but it was a fun project.

 

Looks nice! We need a sound clip.

 

Nicely done!

 

It’s the “ Colorado Loop system”.
This is awesome, see if you can adapt two small resonators for the drone if it becomes bothersome, or dynamtt the back wall.

 

It would be interesting to see the difference between equal length and not. I know it can be beneficial in header design, but I wonder how critical it is in the rest of the exhaust. I also wonder if these extra loops and bends that some guys incorporate slow exhaust flow or have any negative effects that negate the equal length gains. Would be cool to see some data.

 

I'll try to get a sound clip this week.

@j_supra Ditto on everything you said. It'd be cool to see a dyno result of a similar system using that computer tune that allows you to lock in a gear so we can see low RPM power numbers as that's where I believe equal length really helps.

But yeah, maybe just putting on a freer-flowing muffler would get most of the gains I'm feeling, but my thought is, as with header design, timing those exhaust pulses even further down the line should help scavenging even more at low RPM. If anything, the loop and a couple bends balanced the passenger bank so it has the same restriction as the driver's side
At any rate, it feels like it moves much more effortlessly than before without near as much throttle input so it's a win in my mind.

 

It would have been better to push the muffler as far back as possible so it wasn't under the cab but where the back hanger is located, I would have had to weld it to the side of the muffler or use a shorter/louder muffler, neither of which I wanted to do.

On first drive I was thinking, "holy crap, this thing has way too much drone, I gotta find a different muffler or add a couple 1/4 wave helmholtz resonators" as I was slowly driving out of my neighborhood but after it warms up, it's very pleasant with just a hint of drone at that one spot. I haven't towed my camper yet, so the jury is still out on that.

 

Here's a video I made last night since I could open it up a bit. Unfortunately it was raining and snowing, so video isnt great, but first part is while it was still somewhat cold, so more resonance, then some throttle to get up to 55 mph. Added a clip of in town driving this morning with it fully warm. It's pleasant.

https://youtu.be/AkcVZF5ssWU

 

Looks really nice!

I’d love to see more data on this as well. One thing to note is equal actual length when measuring the pipe w/ string does not mean equal equivalent length when it comes to the flow (friction loss) of exhaust gas. I had brought this up once before but assumed I was the only one interested in the nerdy details. In 2.5” pipe, each long radius elbow is equivalent to 4.2’ of straight pipe as far as friction loss goes. To make a 2.5” pipe circle, that is effectively 4 long radius elbows in a row. That one circle of 2.5” pipe is equivalent to nearly 17’ of straight pipe as far as resistance to flow. I think this results in overcompensating on that bank for friction loss. The equal length sound however is probably achieved!

 

I picked up on your friction loss post. It would be interesting to see the difference between flow friction loss and sound wave resonance.

 

For sure. Or even to dyno the same truck. Couple runs with equal length and have another pipe made to be unequal length and dyno again. Would be so neat to see. I also wonder if it leading up to an X-pipe makes it more or less important to be equal length lol. I made a custom exhaust as well and hope I'm not missing out by not running equal length lol.

Well this just further complicates things lol I did not know this... Seems like it would be very difficult to actually calculate it and make it perfectly equal. A failed attempt might do more harm then good. And you would never really know lol unless extensive testing. Interesting!

 

It’s hard to say as that’s a chart for probably a specific type of pipe that’s not exactly the same sweep on the elbow, different material etc. but I do think it highlights how much even one elbow adds to flow resistance. That may also be for water and not air/exhaust which probably changes things. Either way I’d say try and get it close, and let a crossover X or H pipe do the rest as far as balancing out the banks. I do think it’s less critical with the crossover pipe, since that’s a big part of the idea behind it as well as scavenging. Either way, I can say that the SPD system sure seems to sound good in the videos if nothing else! I’m sure this custom setup sounds nice too.

 

I'm interested in the friction losses as well, but we have to remember that the drivers side also has two ~90deg bends and what looks like a few 30-40ish deg bends too. I've added an additional 180deg bend so im sure youre right with adding a little additional loss on the pass.side. It would be awesome to see a true scientific test on this in addition to dyno numbers to see how it plays out. I can understand that with fluids after building my various irrigation systems. but I'm having trouble wrapping my head around those losses with gas/air. Where is the units of measure for straight pipe equivalent? Maybe I missed seeing it on my phone.

 

Badass homemade setup! Reminiscent of a Flugelhorn, imo.

 

That's part of the reason why I designed my own system. Lol. There's always that placebo when buying something expensive, I kinda wanna believe it added power to justify the cost... Or even put up with some quirks. So going in to this, I half expected not to feel any difference. I figured if it sucks or I find it's not performing to my liking, I can cut it up to change it or take it off altogether and I'm out less than $500.

It took me literally months of an hour here and there to build this so I don't have the time, but it'd be neat to see nothing other than the loop swapped for a straight pipe and back to back dynos to see if anything changed.

 

I agree with all of the above! Yep you're right, so many variables, how long exactly is the radius accounting for on the charts etc. I'm not too worried about mine, I'm so glad I put an X pipe. And to me, it sounds unreal! A bit too loud and lots of drone at highway speed but I plan to change up my muffler setup. I just reused the muffler I had previously.

 

Oh, I forgot to mention that the new GMC Denali has a loop on the passenger side straight from the factory! I'll see if I can dig up a picture of it.

 

Dangit!!! You beat me to it!!!

Sounds great! Nice and melodious…

 

I totally agree. That's why I did too. I feel like I built a better or at least comparable system to an off the shelf cat back for less cost. And that includes building from headers back with new cats. I'm happy with it.

I hear ya there. That would be cool for sure. Wish I just had my own dyno to play with and record and collect data comparing mods lol

 

Lol right on!

 

I mispoke, it was't the GMC Denali, it was the Cadillac Escalade V series that has a factory loop:

 

The V does sound amazing.

 

I did equal length, I do see about 10% jump in mpg and 0-60 had about .2s reduction.

There's a math to it, but I'm 100% sure I was off on the calculation, I've also been eyeing on z-pipe, oh well, next year's side project.

 

I like it. Side project of mine this winter hopefully is figuring out how to make pipes that exit outside the truck and still keep it equal length on my SPD system. Towing in 5th at 70mph gets rowdy after a while.

 

Since we're talking exhaust theory...

I've decided on SW LTH next, going to try their cats and keep my OEM on a shelf if needed. But...I want it to be quiet, we do a lot of camping, a little towing, and lots of summer idling to keep the dogs cool.

I'm considering a 2-1 Y into a resonator w/ 1/4 wave and the largest 3.5" muffler I can squeeze under there (Dynomax quiet flow?), then dump around the axle. Hoping dual 3" midpipes to a single 3.5" will have enough flow and still help a bit with scavenging.

 

Also been eyeing the Z-pipe lol Almost snagged it last week.

 

Y'all talking about this pipe?

https://www.blackopsautoworks.com/products/formula-z

 

Yep

 

huh, reminds me a lot of the BORLA switchfire x-pipe for the mustangs and TRX.

 

It's more or less the same concept.

I need to take a video in the tunnels, the equal length definitely makes it sound like it's revving much higher than it truly is.