MamaBear2015

We've been hearing rattling in the back of the car ( 2002 Civic ) and our mechanic said it was the muffler, and recommended a nearby muffler place.

So for years now, I've been hearing that increasing the muffler and tail pipe diameter can add both MPG and a little more power to a car. It was intriguing, because it's the only thing I've heard that gives both at the same time.

So the muffler place turned out to be a Performance muffler place and I asked them on the phone, how much it would be to just replace the muffler, and they said around $150. And how much for the muffler and tail pipe? He said maybe $250. When I got it there, he said maybe $175-$225 to do both, and he suggested not going all the way to the catalytic converter, because the engine was designed for a certain amount of back pressure, and getting rid of some kind of resonator that was in that line too. ( what was that, and why was it there in the first place? )

So the total came to $207. I think he said that they increased the diameter from 1-3/4" to 2" on the parts shown. The car is slightly louder but not bad. Haven't had a chance to drive it much and check the MPG and pickup yet, so I'm not sure what percentage better that all might be. Any idea?

GolNat

iTrader: (7)

I highly doubt you will notice anything but the sound. It’s not much of the pipe and it’s not a performance engine.

Yes the resonator is added to further muffle the sound because most people don’t want to hear the car.

Slumpertcivic

pjb3

An engine does not need backpressure nor does it increase torque. Your shop is confusing backpressure with velocity. Higher velocity and reflected waves help create a negative pressure and pull combustion gases out of the cylinder. The easiest way to increase velocity at lower rpm is a smaller pipe.

Adding a larger pipe does nothing if restrictions remain in the first part of the system.

MamaBear2015

Great. Well, we'll see on the MPG, anyway. It seems to be running a little better, but I hope that's not just wishful thinking.

I'm a former electronics technician, and if exhaust pipe is anything like resistance in a circuit, the length of the exhaust pipe at the given diameters could matter? So this might actually lower the back pressure? Just curious here.

pjb3

In theory a larger pipe flows more and has less backpressure. In practice you are going from a more restrictive system to a less restrictive system so the backpressure occurs before the larger pipe. Measure the resistance across a 100 ohm resister then across a 100 ohm resister with a 10 gauge wire attached. Where do you see the resistance in the system?

I would also point out the stock exhaust system is designed for the engine to operate up to redline and under most conditions you are at lower rpms and flowing much less.

MamaBear2015

Not sure what that last part means, but surely if the manifold exits to the pipe and only goes 6" at 1-3/4", then becomes 2". it would be a big difference, so I thought length would add effective resistance.

sdaidoji

iTrader: (1)

yes, you are right, although some detail differences might exist, but basically electric systems have parallels with mechanical systems such as spring/damper systems or flow systems (mechanical engineer here :P)

of course, modeling them right impacts the outcome of the theory... smaller engines, high or low RPM, etc, etc. (hunh, actually electrical systems also would have the same, thinking about it)

MamaBear2015

Plus, I'm thinking that taking out that thingie between the muffler and the catalytic converter ( what was that - a resonator? ) would lower the pressure some too?

Well, we'll see if it impacts MPG and pep any. Like I said, it could have just been a $50 gamble.

sdaidoji

iTrader: (1)

leave it there. not worth the work

intake, exhaust alone really do not do much other than make the car louder on these engines.

the day i put the CAI (cold air Intake) and passed under a tunnel, I suddenly thought the exhaust had fallen off.
No real meaningful gains in the performance or mileage side. Maybe one pony could be a good percentage for our 125 (when new) engine HP...
stripping down any extra weight might have more impact (other than noise).

I only changed the muffler because the stock one hit my aftermarket rear anti-roll bar

MamaBear2015

Well this exhaust shop already took that middle thing out, when they changed the muffler, so it's gone - no expense - same price. :-)

Is that contraption between the cat and the muffler, called a resonator?
Because they told me that it would just give a deeper tone, by leaving it out, and it did. More bass in the engine sound now.

pjb3

What that last part means is that if an engine redlines at 7,000 rpm and the exhaust system is designed to not be overly restrictive at 7,000 rpm, then at a more normal cruising speed of 3,500 rpm it is flowing half the amount of exhaust and restriction is far less.

If you have 6" of 20 gauge wire connected to 6' of 10 gauge wire, how many amps can you pass through it or what size fuse should you use?

MamaBear2015

Ok, here's an update. This isn't definitive yet, but I had been learning to drive while shifting the automatic transmission around 2000 RPM when possible, to get better gas mileage. It really helped. I was previously getting 30-34 MPG, and with ethanol in the winter, that dropped about 2 MPG to the 29-33 range.

My driving is always a mix of city and highway driving, in the Denver area ( horrible traffic now, with 3 million people! ) and my car is used 90% for business.

My last tankful, before getting the new muffler and getting rid of the resonator, I got 35.4 MPG.

So I just filled up for the first time since this work was done, and it got 37.4 MPG. I HOPE that's an indicator of what this work did, because I've NEVER gotten mileage like that before, with this car - not even close!

pjb3

Single tank mpg are meaningless unless you can guarantee that the tank was filled to the exact same level each time. Even if you fill up at the same pump every time the nozzle will shut off at different times. My average dropped 4 mpg because of very cold weather for a week. Unless you can remove all other variables except the new exhaust system your numbers don't mean a lot.

MamaBear2015

True. Will see...

MamaBear2015

Follow up on this: I've been calculating MPG since this was done. I used to get about 32-36 MPH here in the Denver area ( mile high ) with this car. Now it's been 34-38. Yes, I actually got 38 MPG one time. This is mixed city/hwy driving.

And I don't think we've even switched off of the ethanol yet? THAT usually drops my MPG by about 2 MPG. Really helps the environment, getting 2 MPG less, right?
Actually I think it's crony corporatism, and helps the farmers and politicians, while burning our corn crops, using more energy to make it than we get out of it, and raising the price of products that contain corn. But hey...