Muffler replacement & fuel eonomy

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I've a '98 Chev Tracker 1.6L. Stock muffler and cat converter were
replaced with a 50-series Flowmaster muffler, no cat conv by previous owner. In looking for shop replacement (baffles buzzing), an experienced muffler man tells me that I'd get better fuel economy by re-installing the OEM system (owner gave me the cat and muffler, like new) than going with a new Flowmaster.
Is this true? It goes against all I've ever thought. If anyone has ideas/experience on this, I'd appreciate hearing from you. Thanks.
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We have gone over this again and again, do a google search on back-pressure.
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Mad-Dog
'79 Chevy K-10
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Basic Motor Common Sense 101 - All motors are tuned based on four basic parameters: Best Mileage, Meet the Noise/Emissions Standards of the Time, Most Power, and Durability/Longevity (some would say just enough to get past the waranty period). It's a balancing act based on overall efficiency - if you want more power, expect to use more fuel, emit more pollutants, and possibly shorten the life of the motor all to one degree or another. Better fuel economy sacrifices power to some degree, and you can put all of these into one combination or another until we all get nauseous or go barking mad.
What your mechanic is saying is that you most likely sacrificed mileage for more power when the previous owner installed the Flowmonster, and if you're looking for the best mileage that this motor can offer without sacrficing too much in any of the other areas then the best balance would be to restore it to factory spec. Unless you have the time and money to try any number of combinations and permutations of intake and exhaust systems, air filters, fuel systems, gearing, etc. then run it on a dyno and emissions analyzer over and over and over again, then I think we can presume that the factory got it as close to Good as you can expect without taking out a second mortgage just to find the same thing out for yourself.
Think about it - if a Flowmonster muffler gave your Tracker more power without sacrificing anything else, then dollars to doughnuts the factory would have installed something like it when it was being built. However, for the little more power and noise you got, you probably ended up using more gas and putting out more smog (and maybe even toasting your exhaust valves a touch). A 1.6L motor doesn't pump a lot of air so you don't really need that big of an exhaust.
Cheers - Jonathan
I've a '98 Chev Tracker 1.6L. Stock muffler and cat converter were replaced with a 50-series Flowmaster muffler, no cat conv by previous owner. In looking for shop replacement (baffles buzzing), an experienced muffler man tells me that I'd get better fuel economy by re-installing the OEM system (owner gave me the cat and muffler, like new) than going with a new Flowmaster.
Is this true? It goes against all I've ever thought. If anyone has ideas/experience on this, I'd appreciate hearing from you. Thanks.
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On Sun, 24 Apr 2005 01:08:31 -0700, snipped-for-privacy@webtv.net (larry dee) wrote:

my take on it is this: an after market muffler *will* give you better mileage *if* and only *if* you're not hammering the throttle all the time to hear the new exhaust note. the flowmaster on that 4 banger must have sounded like ass, IMHO. if it was me, I'd reinstall the OE stuff, mainly as it's free and I hate the sound of a loud 4 banger ( with a few very specific exceptions).
-Bret
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My thanx to the responders. I'll check the search engines further for this. Didn't know that the subject had been so thoroughly covered in the past.
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