I have a 2006 Ford Explorer with the V8 and 6 speed trans. I am thinking of fitting a higher flow muffler (Borla or FlowMaster) to increase my mileage. Is it worth doing?? I drive mostly on the highway.
Given all the other restrictions in the exhaust and intake systems (stock cam and valves, manifolds, catalytic converter, etc.), I’d be surprised if you noticed any change in mileage, and would be amazed if you could pay off the cost of the replacement with gas savings.
The gas mileage increase will be minuscule if any. It’s NOT worth it. Chances are there won’t be ANY increase in gas mileage. The engineers at Ford have already designed the max fuel efficient muffler for your vehicle.
The real heroes in the car industry are those guys that can come up with even a miniscule increase in fuel mileage! Believe me, Ford has tried every trick in the book already. Years ago before mileage standards/penalties were in place, you could increase gas milege with some retrofits.
Having said this, a free-flowing exhust system will likely give you more POWER, and might even INCREASE fuel consumption, and REDUCE your gas mileage.
Having said this, a free-flowing exhust system will likely give you more POWER, and might even INCREASE fuel consumption, and REDUCE your gas mileage
Ah yes, the law of unintended consequences in action! 
A performance exhaust system will only lower fuel economy, if it has any effect at all. Letting your Explorer breathe easier means more fuel must be introduced to maintain a proper air/fuel mixture. Who told you a performance exhaust system would give you better fuel economy? If it was someone selling performance exhaust systems, consider the conflict of interest in her or his advice.
It won’t help mileage and will result in a very small increase in power. When you replace the muffler in an otherwise bone stock vehicle what you’re mainly doing is changing the exhaust tone.
You forgot the biggest air restriction of all, the throttle that’s nearly closed most of the time when you cruise at the speed limit. Compared to the throttle’s restriction, everything else is hardly noticeable.
There are a few things you can do about that nearly closed throttle. You can shift earlier to put a higher load on the engine which requires the throttle to be open more. You may be able to regear your vehicle with a taller rear axle ratio which also puts more load on the engine requiring the throttle to open more. You can use the engine for a few seconds to accelerate the car at nearly full throttle and then coast in neutral for a while and repeat. You can get a smaller engine that needs to have the throttle more open to do the job. You can move to the mountains where the thinner air requires the throttle to be more open.
An aftermarket muffler will save gas only because you start driving really easy to keep from getting a noise ticket.
I bet that your Exploder has a stainless steel exhaust system. Is the aftermarket unit made of equal quality metal? I don’t think I would be cutting into a stainless steel system and installing galvanized crap. If you have dual exhaust, the exhaust is probably plenty big enough. I believe that today’s stock exhaust systems are pretty carefully modeled and designed to scavenge effectively. Randomly cutting in and replacing pieces is not so likely to make any improvement.
This could only possibly make sense if you have to replace a the muffler anyway. You might be able to offset the increased cost within the lifespan of the vehicle that way. But that is only assuming you truly get a less restrictive muffler (FlowMasters may NOT be less restrictive than stock!), and you don’t go “vroom, vroom” just to hear that nice exhaust sound. Be advised that any increase in fuel economy will be very slight even given the best-case scenario, though.
I doubt you’ve reached the point of needing to replace the muffler in an '06.
I’ve actually installed a few Borla mufflers for people who also bought into the more power/better economy claims and the mufflers did not improve either one of those categories; go figure.
They do sound good though.