Possibly; if you get a new, higher-flowing exhaust, your backpressure is lowered. Backpressure helps your truck make low-end torque, but it also means that your engine has to work harder to expel the exhaust gases. So, putting flowmasters on might fractionally help your gas mileage, but not by much. A whole new exhaust system would further lower your backpressure and might also fractionally improve fuel efficency, but again, it will not be much.
the flowmaster should help over stock, but it won't be a dramatic gain, besides, there's always that testosterone factor, you hear the nice tone, and you tend to try to keep hearing it... but free flowing exhaust has been well proven to improve efficiency. That is what is behind the talk of 10-20% gain in power and economy by adding headers...
the workhorse:86 F250 4x4 6.9 Diesel 4-spd, 4.10 axles
the other workhorse 92 F350 2wd crew cab,3.55 rear axle, 92 6bt Cummins, NV4500
the project: 78 F150 4x4 shortbed 351 auto Iowa Chapter leader, ASE certified parts specialist
Come on down and join us in the Iowa chapter, or your own local chapter!! Thanks, Roger
fellro is correct, technically the flowmaster should help gas mileage but usually you tend to rev the engine and use excessive throttle and mileage drops. At least for a week or two until you adjust to the new sound
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