I dropped an EJ18 into my Legacy LSi.

 

Does anyone have a clue as to what exhaust mod's might beef up the gas mileage for highway type driving?

 

Should I be looking at the headers all the way back or just the muffler?

I don't mind a little louder but my goal has nothing to do with sound either.

 

I'll probably go with a Dynomax muffler since that sounded and performed well on the XT6.

The stock EJ22 exhaust is probably pretty decent in terms of flow for the EJ18 engine. I don't really see you getting a huge gain in gas mileage by doing anything to the exhaust. If you want to try something, I'd start with the muffler since it's the cheapest. Anything else IMO the benefit doesn't outweigh the cost....if you're just looking for gas savings.

if you're just looking for gas savings.

that was kind of the goal with this car...see how well it can do on the highway. a friend needs an exhaust (midpipe/converter) for his legacy so i could donate mine while he gets a free exhaust if there was a good option for mine.

 

i tried poking around at NASIOC but didn't find much. found enough gas mileage threads but nothing substantial.

 

for the XT6 replacing the stock muffler is about the best you can do for highway gas mileage. high flow converters, headers (though that is only with a stock exhaust), straight pipes, removing the converters, etc make no noticeable difference in mileage. i was hoping someone might have similar experience with EJ stuff.

 

thanks for the notes.

what you'll generally find is that the engine uses the same amount of fuel (FI, of course) no matter what the exhaust is doing unless it's REALLY stopped up. You might get better POWER but no real increase in fuel economy. In the old days, we used to "tune" exhausts to a resonance frequency to attain max power, but "today" it doesn't seem to matter much

XT6 is good for a few MPG if you replace the stock muffler - and it seems like a reasonably stupid design for a muffler, so that makes sense here.