header vs muffler

[goliath1812]

I'm looking into an exhaust.... I have a 2007 sedan, and I wonder if either header or muffler will affect MPG either positively or negatively, assuming driving conditions and styles are the same?

I'm looking at probably the weapon r 4-2-1 header, and haven't really decided on a muffler... I have noticed a MPG increase with an Injen CAI though...but I want to keep upping it :-) any advice?

[ljming99]

Correct me if im wrong.

Stock ECU.

Modding larger air intake + stock exhaust = ECU will run lean.

Increasing exhaust size/ less restrictive exhaust = ECU will run rich.

[goliath1812]

I thought the ECU will "learn" once the battery is d/c'ed and reconnected and would adjust to proper levels....no?

[cali yaris]

^ correct.

[tk-421]

FYI: I have a W*R 4-2-1 header that I may have to get rid of soon. Let me know if you're interested. :thumbsup:

[caineroad]

So in that case, if we put a large air intake, engine will run lean then in turns save more gas, right? all we have to do is never disconnect the battery

[ljming99]

I thought the ECU will "learn" once the battery is d/c'ed and reconnected and would adjust to proper levels....no?

That is what i did when i put in a Simolta Short Ram Intake, i also reset the battery.

Not long after, i installed my flywheel and clutch ...the battery was also removed and there was a reset.

When i finally did a dyno run with AFR, the reading was lean.

[suckerface]

TK, how much would you be looking at for the WeaponR? And what would the difference be between it and the DC?

[Captain Slow]

I really doubt it, but now that I've got my Medalion Touring axleback in place do you think I should reset the ECU Garm? I can't see it having much effect....but I guess it couldn't hurt either.

[baseballfan416]

I know this is an old threat but adding anecdotal evidence...

I've noticed an improvement in mpg with the addition of a K&n filter as well as a weapon-r header. Before I get flamed for this let me justify...

One of the rate limiting steps to better mpg is the necessity for downshifting at low rpm's when the car bogs (usually going up hill). You want to run the highest gear for the lowest rpm (ideally 5th since it overdrives the engine speed). Prior to the filter and header I could not go below 30mph in 5th (on a flat surface), without bogging down and having to downshift to fourth. With the addition of the two items listed above, I'm able to cruise at just about any semi-flat surface in 5th from 25mph and above. This tactic applies to all gears...

So yes, while more "power" translates to more aggressive driving, when driven the same way, the load necessary to maintain engine speed (and stay in higher gear) is decreased via a better breathing engine. Decreased load translates to a lighter gas application and thus better fuel mileage.

If this still isn't plausible enough to justify, look at my fuelly account numbers... Year to year (monthly) averages are up almost 2mpg from last year...And I'm actually driving more aggressively with a higher % in the city (job change closer to home). Even If I could get 50mpg that still translates to a 4% increase in fuel efficiency.

[tooter]

I know this is an old threat but adding anecdotal evidence...

I've noticed an improvement in mpg with the addition of a K&n filter as well as a weapon-r header. Before I get flamed for this let me justify...

One of the rate limiting steps to better mpg is the necessity for downshifting at low rpm's when the car bogs (usually going up hill). You want to run the highest gear for the lowest rpm (ideally 5th since it overdrives the engine speed). Prior to the filter and header I could not go below 30mph in 5th (on a flat surface), without bogging down and having to downshift to fourth. With the addition of the two items listed above, I'm able to cruise at just about any semi-flat surface in 5th from 25mph and above. This tactic applies to all gears...

So yes, while more "power" translates to more aggressive driving, when driven the same way, the load necessary to maintain engine speed (and stay in higher gear) is decreased via a better breathing engine. Decreased load translates to a lighter gas application and thus better fuel mileage.

If this still isn't plausible enough to justify, look at my fuelly account numbers... Year to year (monthly) averages are up almost 2mpg from last year...And I'm actually driving more aggressively with a higher % in the city (job change closer to home). Even If I could get 50mpg that still translates to a 4% increase in fuel efficiency.

My Weapon R also helped low rpm torque. Just be careful when running low rpms in 5th as any engine load is really hard on the crank bearings. A guy I know always used to do that on his Datsun pickup to save gas, and he destroyed his engine's bottom end.

[malibuguy]

leave the car alone for best FE.

I have a WeaponR header & noticed no real yay or nay in FE. The stock muffler has a valve in it to perfectly calibrate the flow for the given load on the motor...its a little restrictive on top end WOT, but everywhere else its spot on.

When I ran a full custom exhaust from the header back, I noticed about a 2mpg decrease in MPG...when i tried...my typical 52-54mpg runs, resulted in 48-52mpg. Beating the car like a redheaded step child...the mileage was about the same.

If your ultimately looking for a little more power, do the mods...2mpg is not a big deal to lose.