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I have a 2005 Trailblazer with the 4.2L i6 and I'm thinking about buying an aftermarket muffler/exhaust. My question is: what kind of muffler or exhaust setup can I get that will not decrease my MPG? I have seen other posts on this forum about people installing aftermarket mufflers and saying that they lost mpg. I've also seen a lot about how this engine needs enough backpressure and sometimes modifying the exhaust system will cause a loss of too much backpressure. I'd like to get a bit better sound from the exhaust but I'm not sure if this is possible without sacrificing fuel economy. Please let me know if there are any options or if I should just keep this factory.
 

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To get a better sound - and that doesn't mean installing a fart can --- you just may have to play an MP3 of a Ferrari at 12,000 RPM really loud and roll your windows down so people can hear it.

Ahem!

I digress ....

With the VVT system - I can see that dropping the sonics and columnar flow-astrophysical thingies can create a problem for the various (2?) O2 sensors trying to keep everything nicely inside EPA Standards.

It has always been decreed that if you tweak one end of the engine, then the other end suffers.

Lower mileage may be the result of more performance --- and if you play, you pay............

...................... or is it just about the noise being used as a mating call?

Double Ahem!

MY bid? Keep it factory as the factory wonks did a pretty good job squeezing the MPG and MPH out of the vehicle before it came off the showroom floor.

Wax and shine and perhaps change the light bulbs for LEDs --- but it's kinda tricky changing the exhaust stuff for more performance and not harm the MPG.

Been there ---- did it all while most of youse guys were still in liquid form .....................
 

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2003 gmc envoy_sle
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Rules of thumb.
Smaller pipes or cat and muffler closer to the ex. manifold. Increases back pressure. Increases torque, decreases HP.
Larger pipes or cat and muffler to the back. Decrease in back pressure. Less torque, more HP.
Being that it's not running a 2+ mile speedway. Torque is more useful. HP doesn't matter if you don't have the distance to get it up in RPM's to produce the HP.
So yeah, if you have to replace it, keep it close to stock dimensions. Don't confuse the computer. Like with any computer's data, "garbage in, garbage out."
 

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2003 chevy trailblazer_lt_ext
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My '03 4.2 has had a MagnaFlow exhaust and K&N intake for over 150k miles with no issues. I highly recommend this set-up for engine longevity and performance. 16 city/22 highway mpg for 14 years now.

I have heard of one mechanic (with or without "superpowers") say a K&N is garbage but all my vehicles and equipment beg to differ. A good intake and exhaust pairing should serve you well for many miles.
 

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We with superpowers know that anything you do to force more or less air into the intake is usually compensated by the ECM to meet federal standards.

I've had cement trucks with their turbos on the clean air side have their fins reduced to stubs because of K&N 'filters' passing dirt and silt into them and generally sand blasting the turbocharger into destruction.

I've had diesel Bobcats lose their turbocharger clean air fins too.

I've traced dirt in the intake past the K&N that is so filthy that you can scrape it up with your fingernails.

Yeah --- I'm retired but when I was working and I found the damage done by K&Ns --- I just couldn't be made mad by slapping me in the face with money.
 

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K&N filters require maintenance. If you don't wash and re-oil them regularly you may as well have no filter. The "filter", doesn't filter, it holds the oil that does the filtering. After a while, the oil gets dirty and acts more like a plug in the system. Or the oil is left to get sucked through thr system, and is no longer there to trap the dirt.
While the statement of a good matching induction/exhaust system is optimal, K&N's are not a "free ride." My race car's twin Weber 44 IDF's showed me that.
I personally don't like the way some with "superpowers" present their observations, but once you decipher the "humor" from info, I find that the info to be accurate.
 

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DDS-09, I USED to run K&N air filters on all of my vehicles that had a K&N air filter listed for it. Did it since purchasing a '99 Silverado with the 5.3 V8 in December 1998. I meticulously maintained the filter - washing and re-oiling. Well, about a year ago I reached into the intake air duct between the MAF sensor and the throttle body and there was a layer of dust all over the interior wall of the duct.

What did I do? I removed the air intake duct, resonator and air cleaner box, washed them out, tossed the K&N air filter into the trash and replaced it with a NAPA Gold air filter. Then, I removed the K&N filters from my other 2 vehicles (including the TrailBlazer), washed the air ducts and related parts, and installed NAPA Gold air filters into them.

No more K&N air filters for me!
 

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DDS-09, I USED to run K&N air filters on all of my vehicles that had a K&N air filter listed for it. Did it since purchasing a '99 Silverado with the 5.3 V8 in December 1998. I meticulously maintained the filter - washing and re-oiling. Well, about a year ago I reached into the intake air duct between the MAF sensor and the throttle body and there was a layer of dust all over the interior wall of the duct.

What did I do? I removed the air intake duct, resonator and air cleaner box, washed them out, tossed the K&N air filter into the trash and replaced it with a NAPA Gold air filter. Then, I removed the K&N filters from my other 2 vehicles (including the TrailBlazer), washed the air ducts and related parts, and installed NAPA Gold air filters into them.

No more K&N air filters for me!
Like I said, I had run them on my race car. That was the thing to do in the 80's. They also gave product certificates for wins. So racing once, some times twice a week I was doing maintenance every week, not to mention checking the carbs. I definitely wouldn't run them on a street car. Only a 50% chance I'd run them on my race car now. Changing good quality air filters every couple of weeks would get expensive, when with due diligence a can of oil would last me all season cleaning and inspecting the whole induction system every week. Which I woild do no matter what filters I ran.
 

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Good to know.
 
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