Flowmaster FlowFX Cat Back - My Experience

Diamond817 · March 20, 2021

My Truck:

2021 Silverado 1500 RST 5.3ltr 8spd. Single exhaust side exit option.

Parts used:

Cat Back – Flowmaster FLowFX cat back part # 717893

Muffler – Flowmaster Series 70 part # 530702

Resonator – Vibrant Performance Ultra Quiet part # 1142

Flex Pipe - RP Remarkable Power 3x8x12 part # RK7551 (on Amazon)

This all started because I wanted dual exhaust. I know there is a factory dual exhaust option. In my opinion the dual exhaust through the bumper looks clean, neat, modern, and finished, but at the same time looks too car-ish for me, so I went with the single side exit exhaust option. I wanted a dual side exit exhaust, with tips, hanging down under the truck look, which is not a factory option as we all know. My original intentions were to bring it to an exhaust shop and have them fab up the look I wanted. At this point, knowing what I know now, I should have just went that route.

Enter the FLowmaster FlowFX cat back part # 717893.

So, looking around at some already made cat back systems I came across the FLowmaster FlowFx cat back system for the 2019-2021 Silverado. It checked all the boxes. Inexpensive (paid around $520), stainless steel, 3”, performance muffler, dual side exit, and big black tips! I couldn’t ask for more.

Ordered. Shows up a promptly. Bring it down to my buddies garage and we throw the truck on the lift and get to work.

Growing up in the 80’s around mechanics and hot rods, FLowmaster was always synonymous with quality and performance. Not so much 40 yrs later.

Stock exhaust comes out easily in one piece. Start mocking up the flowmaster and right off the bat, the front hanger on the straight pipe misses the factory hanger location by 3 inches. Oh boy. So, we proceed to mock up the tailpipes and muffler. The tailpipes line up ok with the factory hangers, not perfect, but good enough where no fabrication will be needed. The passenger side tailpipe is really pulling the factory isolators inward. The muffler outlets could have been a little further apart. But it’s in. So we go back and fab up a hanger for the front pipe to use the factory isolator. Everything looks pretty good at this point, so we tighten up all the connections and proceed to the tips. Passenger side tip slides right on. The driver side, not so easy. The driver side tailpipe end has been expanded from 2.5 inch OD to 2.5 inch ID. WTF flowmaster? It took us a good hour of fighting with the tip and pipe to resolve the issue, but we got it done.

Remote start it on the lift, no leaks, sounds great! Or so I thought.

After a day of driving around, I realize this thing is loud. Really loud. Straight pipe loud. The drone and interior sound level is off the charts. On the highway and cruising around town. The DFM is only making it worse. And the cold start is explosive. Your neighbors will hate you. All I can think is what a mistake this was.

I need to a solution to quiet this thing down a bit. And I’m not going back to the stock exhaust because I am very pleased with the look of the dual tips hanging out the back.

I start looking at muffler options to replace the FlowFX muffler in the system. I decide to go back to FLowmaster to see if anything will directly fit in place. The 70 series is the “quietest” muffler in their lineup, uses the delta flow chambering, and is a close match to the inlet and outlet measurements. So, I go ahead and order the FLowmaster Series 70 part # 530702. Which winds up working out very well dimensionally. The outlets are .75 inches further apart than the FLoFX muffler which relieves the pulling on the passenger side isolators.

Now I have to remove the front 3 inch straight pipe to cut it down because the series 70 muffler is much longer than the FLowFX muffler. No big deal really. But before I install the new muffler I start to wonder why the factory exhaust has a flex pipe in it and the Flowmaster system doesn’t. So I do a little research by checking out different cat back systems for this truck, including the systems GM offers. I find there is really no consensus on this as half of the cat back systems incorporate a flex pipe and the other half do not. Even with GM’s cat back offerings, one system has a flex pipe and the other does not. So I decide to go ahead and air on the side of caution and add in a flex pipe (RP Remarkable Power 3x8x12 part # RK7551 (on Amazon)).

The new series 70 muffler and flex pipe are installed. This thing sounds great now. The delta flow chambering changed the sound from a race boat sound to a tuned V8 truck sound. But, it was still a little loud for me* on cold start up and idle. I decide to try adding a resonator into the system to knock the edge off the sound. I come across the Vibrant Performance Ultra Quiet part # 1142 resonator. Looks like the perfect option. I add it in before the muffler. All I can say is perfect! The sound and noise levels at start up, idle, around town, and highway cruising are perfect. Cold start and idle are tame. Around town is a nice deep tone that’s not obnoxious. And with the cruise set at 72 on the highway it sounds like a stock exhaust.

That DFM is still an ear sore around town at this point. I need a solution to remedy this. I decide to try the Range Technologies DFM disabler. I have to say, it worked, and flawlessly. Now the truck looks and sounds perfect.

Edited March 20, 2021 by Diamond817

Diamond817 · March 20, 2021

Dual side exit.

Edited March 21, 2021 by Diamond817

Diamond817 · March 20, 2021

FlowFX Cat Back and the Series 70 muffler below.

Edited March 20, 2021 by Diamond817

Diamond817 · March 20, 2021

Vibrant Ultra Quiet Resonator.

Edited March 21, 2021 by Diamond817

Diamond817 · March 20, 2021

Flex pipe, Muffler.

Edited March 21, 2021 by Diamond817

Sublym808_RST · March 23, 2021

I was thinking about ordering this kit through 4WheelParts. From the videos I've seen on YouTube, it sounds really good. Now, your review of it has me on the fence. I may consider going to a local exhaust shop and price a custom setup. Is there anyone else that has installed the FlowFX Cat-Back on their 5.3 T1? If so, what was your experience like with this setup?

Diamond817 · March 23, 2021

3 hours ago, Sublym808_RST said:

I was thinking about ordering this kit through 4WheelParts. From the videos I've seen on YouTube, it sounds really good. Now, your review of it has me on the fence. I may consider going to a local exhaust shop and price a custom setup. Is there anyone else that has installed the FlowFX Cat-Back on their 5.3 T1? If so, what was your experience like with this setup?

The FlowFX did what it was supposed to do, make a lot of noise and look good. The quality control at Flowmaster is questionable though. So, if you're intention is to make a lot of noise and look good doing it, it fits the bill.

I'll try to attach sound clips of the FlowFX and the Series 70.

Edited March 23, 2021 by Diamond817

Diamond817 · March 23, 2021

FlowFx muffler.

Edited March 23, 2021 by Diamond817

Diamond817 · March 23, 2021

Series 70 muffler and Ultra quiet resonator.

*Can't upload video for some reason.

Edited March 23, 2021 by Diamond817

Sublym808_RST · March 23, 2021

1 hour ago, Diamond817 said:

FlowFx muffler.

There's no audio in this clip. I'd rather not spend the $700 it would cost for this exhaust. I'm sure that it would be cover under warranty but, the hassle of returning it and additional shipping time to HI doesn't seem worth it to me.

Edited March 23, 2021 by Sublym808_RST
Sent too soon