the muffler and exhaust mod thread

[hackish]

Originally Posted by 2005_rs

My magnaflow installation looks alot like your pic in the o.p. The noise was horrible until I added a 9" tailpipe section onto the muffler in order to terminate the exhaust at the bumper. That quieted it down a lot. I think the sound was resonating off the inside of the bumper and underneath the car until I made the change.

One other thing to add with this sort is that a straight-through resonator will make a huge difference in lowering sound. Even the skinny bottle style resonators go a long way and they're relatively easy to fit on many vehicles. I used to install a lot of these on kids' cars when they got too many noise tickets.

[BrianAbington]

If you add a muffler and find the exhaust is to high pitched and farty replace the mid resonator with the longest glass pack you can find. This will deepen the tone and de-fart it quite a bit.

[oil pan 4]

Originally Posted by Diesel_Dave

but I don't see how 9:1 with gasoline can be anything but bad.

What am I missing here?

Its common for them to run 10:1 A/F on turbo gas engines under full load. They do this for a few reasons. The very rich fuel mixture greatly reduces the chance of preignition and detonation. All that fuel cools the intake charge and any liquid droplets of fuel would go into the combustion chamber and cool the hot spots that will form on the piston, spark plug creamic and grounding arm. The very rich mix its self also cools combustion temps.

Your gasoline engine's air fuel mixture will auto ignite well under 600'F, you want to keep your total compression temperature at the time of spark plug firing well below this.

Running the calucation for a gas engine with a 10:1 compression ratio with 73'F intake air at 1bar gives me compression temp of about 890'F.
Run the numbers for my diesel, 22:1 gives me over 1400'F of compression heating.
Thats why turbo engines blow apart some times when they go lean, they loose that fuel cooling provided by the 10:1A/F mix, when the leaner A/F mix is compressed by the piston it gets hotter than it did with the 10:1A/F, when the air fuel mix hits >530'F it goes boom, no more engine.
When you change your starting values for Temp and Pressure like for a turbo diesel engine with no intercooler your adiabatic compression numbers go wild.

You may be wondering why the 10:1 C/R engine's adiabatic heating calc yealded a number that was higher than the auto ignition point of gasoline?
Adiabaitaic compression is figured only for the compressing of air, not air and fuel, factoring in the fuel evaporation could be done but the effect the very rich fuel mixture has on the compressability charastics of air and how the liquid droplets act in the hot combustion chamber is not known to me.
Also the spark plug ignites the A/F mix in an N/A engine well before the piston is at top dead center. So when the spark plug fires, at 30'BTDC or more your C/R at that moment might be 7:1 or 8:1.
Also the faster your N/A engine spins the less your cylinders are filled (in most cases, not all) typically your cylinders are 90% full +/-5% at full power. Some times with more engine speed your volumemetric efficiency will go above 100%, this doesn't happen on street driven N/A engines.
So a 10:1 C/R on paper isn't really 10:1 C/R inside the engine.
In a turbo gas engine, as you build boost your ignition retards from its peak advance and moves back closer to TDC, so instead of lighting your A/F at 30-38' BTDC like in an N/A gasser a gasser with a power adder such as turbo, supercharger or nitrous can have its timing as low as 10'BTDC when its running at full power. So a turbo has more heat, more compression to deal with and there for is more trouble, this is where things get tricky.

I say Diesel engines are easier.

[SiVX]

Originally Posted by Diesel_Dave

Correct, a non-lean burn fuel injected gasoline engine will adjust the fueling based on the O2 sensor readings, so as to keep the AFR right near 14.7:1.

So lean burn does not do this? If that is the case then why do WAI on the VX give us better FE? I would think the O2 is seeing "less" oxygen, thus reducing fuel... I am new to alot of the theory tho.

Originally Posted by hackish

I spent 10 years tuning vehicles, everything from hyundai accents up to exotics any everything in between. I only skimmed the thread but I'll add a few details in here that will hopefully correct a few things and add in a bit of info.

Reducing the backpressure will improve fuel economy significantly while accelerating. Steady state operation will make more gains on some vehicles - especially the EGR equipped ones. If the engine wastes less energy pushing the exhaust down a restrictive pipe through a restrictive muffler then more energy is left to turn the wheels.

I had a 1993 Civic VX with a crappy restrictive 1.25" crush bent pipe. Finally it rotted off so I bought the cheapest stainless setup I could ($150 at shop cost). With no other changes in driving habits I picked up 7% and that was with at least 5000km of test data on either side.

What is steady state? Remaining at a constant RPM/ lean burn? I also own a VX, bought recently. It has a newish stainless pipe from the cat back. Just measured diameter from outer circumferance. Got a nice 2" pipe.

I'm getting mixed signals about pipe diameter. Not sure if it will throw my O2 readings off, while creating less backpressure...

[California98Civic]

Originally Posted by SiVX

So lean burn does not do this? If that is the case then why do WAI on the VX give us better FE? I would think the O2 is seeing "less" oxygen, thus reducing fuel... I am new to alot of the theory tho.

Here is how I have come to understand the workings of a WAI (though this is off thread topic... but okay). The volume of the intake air increases because it is warmer and expanded, but it's lower O2 content relative to volume makes the ECU adjust the fuel downward by shortening the injector pulses. What saves fuel is the fact that in order to get the same power you need to open the throttle more, reducing your parasitic losses due to the engine's need to pump in air through the throttle. You are reducing so-called "pumping losses" and not really leaning-out the air fuel mix. That's the theory I have seen. But my car, on the freeway, runs very lean when I pulse and glide with the engine-on. I think that is partly about my ignition timing advance.

[mcrews]

an added thought on diameter of exhaust pipes.
the chart always refers to the MAX hp. So unless you are a race car you are at max hp MAYBE 1% of the cars life. Remember MAX HP is at aprox 6k rpms. how often do you hold 6000 rpms??????
The other day my scangaugeII recorded 30hp while doing 60mph at 1812 rpms. My car is rated at 340hp V8.
I certainly dont need to 'open up' the stock system to get better 'performance/mpg'

[hackish]

Originally Posted by SiVX

What is steady state? Remaining at a constant RPM/ lean burn? I also own a VX, bought recently. It has a newish stainless pipe from the cat back. Just measured diameter from outer circumferance. Got a nice 2" pipe.

I'm getting mixed signals about pipe diameter. Not sure if it will throw my O2 readings off, while creating less backpressure...

Steady state is cruise. Carmakers often have to balance performance (responsiveness) with emissions and fuel economy. Modern control programs are much better than the obsolete stuff like in a VX. With DBW throttle every movement of the gas pedal is smoothed and translated into a torque request. The control routine will then do whatever it deems necessary to deliver the requested torque. Sometimes this means kicking it out of EGR, sometimes adding extra fuel and timing etc.

With a traditional cable driven throttle you would have a very sluggish engine with lots of "hesitation" as it pulls fuel and adds EGR to the mix. At one point I did some mods to my EGR to increase the mixture and you could feel the car when it kicked into EGR mode on the highway.

Unless you have an exhaust leak don't worry about throwing off O2 readings on a VX. Those cars ran an expensive NTK L1H1 (or L2H2) sensor that is quite precise and properly temp compensated. With aftermarket exhausts and increased flow the emissions sometimes go up because the cat won't hold as much heat but a few rolls of fibreglass exhaust wrap can happily fix this.

[hackish]

Originally Posted by mcrews

an added thought on diameter of exhaust pipes.
the chart always refers to the MAX hp. So unless you are a race car you are at max hp MAYBE 1% of the cars life. Remember MAX HP is at aprox 6k rpms. how often do you hold 6000 rpms??????
The other day my scangaugeII recorded 30hp while doing 60mph at 1812 rpms. My car is rated at 340hp V8.
I certainly dont need to 'open up' the stock system to get better 'performance/mpg'

30hp for a 60mph cruise sounds about right.

Forget about your pipe charts and such, they're wrong and you're looking at the problem the wrong way.

For exhaust systems, better performance and better fuel economy come from reducing pumping losses. It does not matter what the theoretical maximum flow of a pipe is. If you're throwing away energy pushing exhaust through a restrictive system then the energy is costing you gas mileage.

In my experience with V8's big improvements are made with headers. The trick with that unfortunately is keeping the cats hot enough that you're not trading fuel consumption for emissions output.

A lot of the newer PCMs support per cylinder trimming but I'm still waiting for some testing to do cylinder balance - I'm certain this will pick up more efficiency.

[alowe2169]

I think the focus should be more on useable torque not peak horsepower. Ive read somewhere that a gasoline engine's peak effeciency is usually pretty close to its torque peak. I would think that focusing on an exhaust that compliments the torque curve would be best for FE. Just my $0.02

[MTXA]

I read through this thread last night before going to sleep. I had the craziest dreams about mufflers, catalytic converters, y-pipes, resonators, and headers. I've gotta tell you, when I woke up this morning I felt exhausted.