Hi all,

Replaced the stock "super muffler" on my 2008 Unlimited with a Magnaflow #11244 6"x14" oval straight thru muffler. It is significantly smaller and lighter and gives the 3.8L a nice exhaust note. Not loud at all and unobtrusive in the cab.

However, I seem to have lost at least 1 mpg or more. Am considering going back to the stock muffler. Have considered adding a flow restrictor to simulate the stock backpressure. Any thoughts on this would be welcome.

 

That 1mpg gallon loss may be because you put your foot into it a little more cause you can hear the engine now, maybe

 

That could be it.... Airaid did the same for me.......
Does it have more get up and go on take off or when on the highway?

 

I would like to add that it doesn't seem to have anymore "get up and go" than it did with the stock muffler. Possibly a little on the top end. Low end the same or less.

 

understand that you would not be trying to simulate the stock back pressure. You want to simulate the stock flow velocity. thats a common misconception.

You shouldn't expect to gain noticeable HP/TQ by just swapping the muffler. Their are too many restrictions before the muffler.

 

Not sure how many tanks of fuel you have ran through, but my experience has been that any change isn't really dialed totally in until the third tankful. The first one gets 90% of the way there and by the end of the second you should be all the way to the achieved results but your calculations might be a hair off until that third tankful.

One thing I noticed was that with the stock exhaust I was driving my six speed totally by feel as I couldn't really here the exhaust. When I switched it out it had enough of a tone that I started shifting on sound. Definitely changed my perception of where the shift points should be and I was less apt to shift out of the power band.

I would also get some sort of a performance drop in filter for the air box. You've freed up your exhaust a bit and making the intake side breath better will get the best out of both.

As mentioned previously, it's all about exhaust gas velocity and without hesitation the smaller can and pass through design should help. Less exhaust gas heat displaced means the velocity will stay high and heat barrier coatings or even on the cheap, black grill paint will help albeit modestly.

 

JPop I also have the 6 spd. and likewise my main objective was to be able to hear the engine for shifting points and starting from a stop. Not necessarily for a performance gain and definately not for a loss. Will give it more time and run through a couple more tankfulls.

It does make sense to match the stock flow velocity rather than restricting the flow.

 

in a way, raising flow velocity does sometimes mean slightly restricting. For example, flow velocity would be lower on a 3" exhaust, and higher on a 2.5" exhaust. you want to be able to get as high a flow velocity as possible without causing back pressure.

honestly, your MPGs should be the same now as compared to stock. because you haven't freed up any of your exhaust...you are still running the stock exhaust. By swapping out the muffler all you have really done is change your exhaust note.

 

The Stock Super Can does slow down exhaust velocity as it's a gigantic heat sync. I'm fairly certain the EGT at the tailpipe will be higher with the magnaflow than with the stock can.

 

that's 100% accurate. however, changing out the last 18 inches of an exhaust that measures 9 ft from the twin pipe collector will not make a a noticeable difference in gas mileage or power.