18 Silverado 4X4 5.3 V8 Cat back Dual Exhaust Conversion

Dvaneck · May 25, 2019

Hello I'm new to this forum,

As the header say's I have an 2018 Silverado 4X4 5.3, with 4500 miles on it,

I just did a Cat Back Dual exhaust conversion, magnaflow and the truck sounds great,

But I'm noticing , that there is actually less power and my MPG dropped from 20.3 average

to 18.2 average, considering I was expecting a small boost in both, do I need to get a power chip

or what can I do to fix this issue, any suggestions would greatly be appreciated

Edited May 25, 2019 by Dvaneck
Typo

sirooga · May 25, 2019

I feel the same thing happened to me I have a 16 with the gm Borla dual exhaust and the gm cold air intake. I believe this is what has lowered my mpg also.

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CamGTP · May 25, 2019

I can see zero reason for a power loss or mpg loss on a stock vehicle like this.

If you're telling me that even after the exhaust passes through 3 cat converters, your new more free flowing piping and muffler setup that you lost mpg, I'm not buying it.

I've never had a stock vehicle lose mpg just because I changed the cat-back.

You're driving style is more to blame than anything. Or changes from the environment, using the A/C more, cooler weather or warmer weather. Those variables can totally change the avg miles per gallon by 1-2mpg without you even thinking about it.

Without a dyno, it's impossible to see if the engine makes less power. Seems like it's all in your head to me.

16LT4 · May 25, 2019

Better sounding exhaust = driving to hear the sound, which means heavier throttle input.

I laugh at the money wasted on "cold air intakes." Every factory air intake is cold air. If using a "hi-flow" filter, then that means less is being filtered, and the MAF is also adding more fuel to hit proper stoich with your additional air, so that's also where your increased fuel is coming from. More air = more power (but also more fuel).

Dvaneck · May 25, 2019

Yes I'm serious, I thinking it has to do with the computer trying to figure out what has happened,

and No my driving style is consistent, that's why my MPG always stays about the same, also the tech who did this for me

said there was a flap in the exhaust after the cat which he removed, don't know why Chevy put one in it, thought that was

really weird , also its only been a couple of hundred miles since I did this, and I'm hoping that the computer with adjust itself

accordingly in a few more hundred miles,

Also would you recommend disabling the active fuel management system to get rid of that annoying burble in v4 mode

and what would be the best chip or programmer to use?

thank you in advance

Edited May 25, 2019 by Dvaneck
More topic

CamGTP · May 25, 2019

There are no sensors or anything past the 2 primary cat converters, what is the computer going to do to adjust when to "it" nothing is different?

The flapper is to cover up the V4 sound waves, removing it now lets you hear this burble. Disabling the AFM/DoD would remove the sound for good.

There is no such thing as chips anymore, that went away way in the 1990's. Everything since 1997 in basically all the GM platforms require a handheld tuner or specific software to edit the calibration inside the computer and flash back over it.

2017+ model year trucks generally cost more to tune and of course anything you do will void the warranty on the powertrain. Your options are to buy a tuner like HP Tuners and learn it, you'll be in that for $500-600 easy plus all you time. A dyno shop would require that much or maybe more to tune it. You could look into diablo handhelds or similar but I couldn't tell you how well those work or costs.

If you're avg anywhere from 18-20mpg with mixed driving, you are already doing at or better than what the vehicle is rated for. I'd say you are doing great. The majority of people probably get less than what you are getting and are still okay with it because it's a truck.

Vindicta_Mihi · May 25, 2019

Dvaneck- I deleted my dod/afm immediately upon getting my truck. I definitely recommend it, as I had issues with the technology at that time; when the computer shut down cylinders depending on where it was in the cycle it tended to use/burn oil in most cases for me. I have a superchips programmer I could sell you for a decent price, its for my 2014 gmc sierra but should work for you nonetheless. Hit me up if youre interested as I have efi live now and dont need it.