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Magnaflow muffler

alanhornet

By alanhornet
in Engines & Drivetrain

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scott19677 Senior Enthusiast

scott19677

Posted
Posted

Here's the thing. If you don't know too much about the flapper and resonator you would most likely NEVER even notice the V4/AFM issue. Its just some of us are more "tuned" in to how our trucks behave and drive. Same thing as with the catch can issue. If no one had ever said anything, you'd never think about it and probably get 100,000+ miles with no worries. But there are a lot of people like me who have had a dozen or more GM trucks that really notice things like this. The worst thing you can do is listen to muffler shop guys. If you want a moderate to aggressive sound you need to get a tune to delete V4 and loose the resonator and flapper or you can drive in M5 all the time and lookout for that "choppa".

 

Bottom line is if you want a V8 to sound like a V8 you gotta drive it in V8.

volrus Enthusiast

volrus

Posted
Posted

Beware of one thing that I just discovered yesterday. Installed an MF muffler and removed the flapper. My gas mileage suffered dramatically on a full day of driving on the Interstate. Just yesterday, drove round trip about 340 miles 95% on the interstate and averaged 17.5 mpg. That's down from 20 to 21.5 I typically get on the same trip. Not very happy about that lol. I didn't expect it to necessarily get better, but certainly didn't expect a 15 to 20 % drop.

robvas Enthusiast

robvas

Posted
Posted

It's not the muffler or flapper. I got 21.5mpg on the highway (70+mph) in my 6.2 with no flapper and a 3.5' Magnaflow

HondaHawkGT Senior Enthusiast

HondaHawkGT

Posted
Posted

Yeah either the fuel trims were off due to the exhaust velocity change or you had the same thing happen to you that happens to most guys that get a nice exhaust... You get into the throttle so you can hear that sweet v8 scream haha.

volrus Enthusiast

volrus

Posted
Posted

Yeah either the fuel trims were off due to the exhaust velocity change or you had the same thing happen to you that happens to most guys that get a nice exhaust... You get into the throttle so you can hear that sweet v8 scream haha.

What are "fuel trims"? Lol, believe it or not, I was actually very cognisant of the fact that I had to resist the urge to lay off the throttle. Something definitely isn't right though, I've made that same trip many times and always get at least 19.5 and usually 21 or 22 for the entire trip and no matter which metric I was watching (avg mpg for 25 miles, avg mpg for 50 miles, avg mpg for 400 miles, or avg mpg for the trip), they were all lower.

ikaika1984 Enthusiast

ikaika1984

Posted
Posted

It's not the muffler or flapper. I got 21.5mpg on the highway (70+mph) in my 6.2 with no flapper and a 3.5' Magnaflow

So if it's not the flapper, then what caused the decline for him^^^^^

 

Sent from my SG Note 4 on Tapatalk

kennerz Enthusiast

kennerz

Posted
Posted

These trucks take a long time to "learn" or the factory programming take a long time to adjust the air fuel ratio ("Fuel trims") for changes/increases in airflow. SO you need to do one of a few things. Drive it until it adjusts( A tank or four). Unplug the negative battery terminal overnight and let the computer re-learn from scratch, or get it tuned if you want best results and can't wait.

 

Your purposely using light throttle, now with the new combo it's using more fuel at the same light throttle because it compares it to how it was before. Reset the ECM (unplug battery) then drive it around for a week or two and see if nothing has changed. What that tells me from your experience is the factory exhaust with a flapper and resonator & a muffle is restricted.

robvas Enthusiast

robvas

Posted
Posted

So if it's not the flapper, then what caused the decline for him^^^^^

 

Sent from my SG Note 4 on Tapatalk

How he's driving. The factory muffler isn't much of a restriction.
kennerz Enthusiast

kennerz

Posted
Posted

Between the flapper, factory muffler and resonator there has to be some restriction. You mean a spring loaded valve isn't going to be any restriction? I run an open core 14' magnaflow race muffler on at least two vehicles and they picked up noticeably, especially torque(while using a 3.5 over a 3'). I agree that most mufflers and cat backs are not effective at producing any gains. However a properly designed open system with the " right " length and combo of parts will give you "something" if your lucky maybe 10 rwhp and 20 rwtq. When you have 420 fwhp it isn't a huge gain but it's something.

 

More air flowing, the ecm will use more fuel all other things equal.

Lgetz Senior Enthusiast

Lgetz

Posted
Posted

Beware of one thing that I just discovered yesterday. Installed an MF muffler and removed the flapper. My gas mileage suffered dramatically on a full day of driving on the Interstate. Just yesterday, drove round trip about 340 miles 95% on the interstate and averaged 17.5 mpg. That's down from 20 to 21.5 I typically get on the same trip. Not very happy about that lol. I didn't expect it to necessarily get better, but certainly didn't expect a 15 to 20 % drop.

Others may chime in but another factor affecting your mileage is the winter blend of fuel in use now. I noticed my mileage went down some as well over the past 2-3 weeks and same usage as before.
Sierra Jon Enthusiast

Sierra Jon

Posted
Posted

Others may chime in but another factor affecting your mileage is the winter blend of fuel in use now. I noticed my mileage went down some as well over the past 2-3 weeks and same usage as before.

 

same here... didn't change muffler (yet) either. and I'm aware of the drop due to remote start - it's not that... I'm talking a new 25 mpg average vs a month ago.

volrus Enthusiast

volrus

Posted
Posted

Well, it has gotten a little better since I posted this originally. I assume the ECM figured it out a little. However, it's still struggling a little which tells me it could certainly be the winter blend. I wouldn't have expected to get the winter blend here in TN until early December though.

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