Can a non oem muffler make MPG alot less?

[ericem]

Hi, just wondering if that could be why my fuel economy isn't so great. My muffler is VERY loud surprised how quiet it is inside, but if ur outside it sounds like a real sh*t box, with very little throttle its still loud, and if u floor it, sounds like it misfiring, its very funny i odd to get a video.

[nipper]

yes it can have an effect. But first the more obvious questions, when did the MPG take a dump? If it was right after the muffler, thats a red flag.

 

You dont say how many miles, so have you done a full tuneup recently? How old is the O2 sensor? Tires properly inflated? Junk out of the back of the car?

 

 

nipper

[ericem]

yup car's empty, but the o2 is $80 the muffler is $100 OEM. and my dad said it was replaced with OEM o2 not to long ago. I never really noticed the MPG to be honest, didn't pay much attention till now. and the the plugs, nto the wires yet, fuel injection clean, cleaned the throttle body, did the pcv(OEM) fuel filter, air filter, sprayed the MAF.

[wondercow2]

What kind of muffler are we talking about here? If you moved up to a 3" fartcan, you've killed anything resembling backpressure in your system, and your mileage will suffer.

[ericem]

What kind of muffler are we talking about here? If you moved up to a 3" fartcan, you've killed anything resembling backpressure in your system, and your mileage will suffer.

 

don't know some guy installed it, and it blows real bad

[wondercow2]

don't know some guy installed it, and it blows real bad

 

You really need to give some more details if you expect a real answer.

[ericem]

All i know is its the same size pipe, just this muffler is very loud.

[Hodaka Rider]

A better flowing exhaust will usually give you better mileage - assuming you don't use the extra power that comes with better flow.

 

What kind of muffler are we talking about here? If you moved up to a 3" fartcan, you've killed anything resembling backpressure in your system, and your mileage will suffer.

 

Don't even start with that. Backpressure=bad. Start reading here: http://auto.howstuffworks.com/question172.htm more info: http://en.wikipedia.org/wiki/Exhaust_pipe yet more: http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

 

 

It also does not matter what size the outlet is on the muffler, and even if the inlet was 3", it would have been sleeved down to match the rest of the piping.

[Manarius]

So, I think, in short, unless you swapped to a more restrictive exhaust, your muffler is not the problem.

 

 

And, I think I'd argue that putting a 4-inch pipe from your NA engine would be a bad idea. NA engines need some sort of back pressure or else it burns exhaust valves.

[Jimmyowensfan20]

unless you live in a testing state...core that cat out and milage WILL improve!

[Hodaka Rider]

NA engines need some sort of back pressure or else it burns exhaust valves.

 

Also false. Read some of the stuff in the links I posted, as well as some more research.

 

"the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before."

 

The "burnt valve" thing may have applied to some non-fuel injected engines, as well as FI engines, where proper tuning did not follow the free flowing, low backpressure exhaust. Note the "causing more air to be drawn in" part? More airflow needs more fuel. More air + more fuel = more power.

 

 

Basically, though, your engine will only perform well with exhaust diameter up to a certain size. Above that size, power levels taper off, and you lose low end. Proper extraction can only occur when the pipe is sized right for the engine, with low restriction (restriction=backpressure).

If you have a low-backpressure exhaust say, 2.25" diameter with a good muffler, and compare it to a 2.25" diameter exhaust with nasty pinch-bends and a poor muffler design (thereby giving the engine the backpressure you say it "needs"), the low-backpressure exhaust will give you better performance, and you will NOT burn valves as long as you: a) make sure your carb is still jetted OK for the flow or: have a modern fuel-injected engine that can compensate for better flow.

[Manarius]

All right. I understand that. My dad told me a story once where he put a rather free flowing exhaust on his 1970's model Toyota and it burnt the exhaust valves on it. I was not aware that FI engines didn't behave in the same fashion.

 

http://www.proficientperformance.com/tech_back_pressure.php

[nipper]

All right. I understand that. My dad told me a story once where he put a rather free flowing exhaust on his 1970's model Toyota and it burnt the exhaust valves on it. I was not aware that FI engines didn't behave in the same fashion.

 

http://www.proficientperformance.com/tech_back_pressure.php

 

NO its not that fuel injection engines changed that, its the fact that 30 plus years of engineering, emissions and materials technology changed that.

 

 

nipper

[OB99W]

unless you live in a testing state...core that cat out and milage WILL improve!

Right, the world needs more pollution, and a constantly lit MIL and P0420 code are fun.

[Hodaka Rider]

NO its not that fuel injection engines changed that, its the fact that 30 plus years of engineering, emissions and materials technology changed that.

 

 

nipper

 

Right. An older FI vehicle might still have issues if it can't compensate. Just as a newer ('80s) carb'd Subaru might be fine, because it can compensate a little with the "feedback carb" system.

[ericem]

You know what actually what are these "exhaust valves" ? I remember my muffler was very loud with the stock one as well for some reason Maybe it was because one of the baffles were raddling but it sounds the same. Maybe something else is the problem.

[Jimmyowensfan20]

if you aint out in the back yard hugging a tree and don't have to pass emission tests in your state core that cat out and make significant gains....

 

not just my opinion....FACT!

[ericem]

if you aint out in the back yard hugging a tree and don't have to pass emission tests in your state core that cat out and make significant gains....

 

not just my opinion....FACT!

 

i do need to pass or i don't get my sticker and i already pass with flying colours.

[86BRATMAN]

if you aint out in the back yard hugging a tree and don't have to pass emission tests in your state core that cat out and make significant gains....

 

not just my opinion....FACT!

 

It really does make a difference. I wouldn't condone this sort of thing(or would I).

 

Think about all the pre-convertor era cars and all the stuff they throw into the air. They will give off more emisions than a modern vehicle without a cat any day of the week.

[OB99W]

if you aint out in the back yard hugging a tree and don't have to pass emission tests in your state core that cat out and make significant gains....

 

not just my opinion....FACT!

Here are some real facts:

1) By itself (see #3), a catalytic converter that's in good condition doesn't have much of an effect on gas mileage, and removing the core won't improve things to any significant degree.

2) An obstructed cat can lower gas mileage, but replacing it resolves the problem.

3) An engine that uses a cat is designed to run near the stoichiometric point when possible (light to medium loading; heavy loads require a richer mixture). All other things being equal, getting better mileage requires running leaner. However, removing the catalyst doesn't turn the engine into a lean-burn one. If the engine management is modified and the mixture is leaned, engine temperatures go up significantly; an engine that's not designed for it will have problems.

 

Just to show that I'm not naive:

4) Cats are not environmentally perfect -- while they reduce certain toxic exhaust gases, they increase the output of greenhouse gases that can lead to global warming.

 

Someday we might have better emissions controls, readily available alternative fuels, etc., but for now the catalytic converter is what we've got, and defeating it gains little but more pollution.

 

By the way, I don't hug trees, but I do care about them and the rest of the planet. It's too bad that the environment means so little to some people; perhaps they don't expect to have a future, and don't have any family that might, either.

[88whitecat]

Think about all the pre-convertor era cars and all the stuff they throw into the air. They will give off more emisions than a modern vehicle without a cat any day of the week.

 

I agree with you but only to a point. Pre-cat cars also burned leaded gasoline. I have personally seen older motors rebuilt and tuned for unleaded gas and pass with better emissions than some newer cars. The way it was explained to me was the longer stroke of older engines allowed a more complete combustion of the fuel than the newer short-stroke, high-rpm motors.I have nothing to back that up at the moment; but maybe somene else will have some info?

[nipper]

I agree with you but only to a point. Pre-cat cars also burned leaded gasoline. I have personally seen older motors rebuilt and tuned for unleaded gas and pass with better emissions than some newer cars. The way it was explained to me was the longer stroke of older engines allowed a more complete combustion of the fuel than the newer short-stroke, high-rpm motors.I have nothing to back that up at the moment; but maybe somene else will have some info?

 

That was true up till the mid to late 80's. Once fuel injection came about, that advantage went away. I personally owned a few 1960's cars that met 1980's standards.

 

The only thing that was changed really was valve seats. What WILL happen is that a rebuilt engine from the the leaded fuel era will last 3 times longer then an original untouched 60's engine due to the removal of the lead. Lead was a huge cause of sludge in the engine back then. Now the cause is moisture, and it isnt that common (across the board).

 

nipper

[subie94]

welding job (wasn't me)

 

stock muffler

http://s24.photobucket.com/albums/c34/beretta92d/?action=view&current=stockexhaust.flv

 

unsilenced (not much back pressure)

http://s24.photobucket.com/albums/c34/beretta92d/?action=view&current=vidclipwithoutsilencer.flv

 

 

running with silencer in,sound is about half and the last 2-3 fill ups,i figured i got around 23-24mpg..having silencer out,i get about 20-21.(depending on how i drive that week too and all my driving is 99% city)

[ericem]

thanks subie94, exactly what i wanted to know!