Quiet Performance - muffler selection

[Canyonero]

I have a flowmaster muffler with no cat on 3-inch pipe, and I don't like it much. I like the low rumble, but I don't want it to be obnoxiously loud above 3k RPM like the flowmaster. I want a consistent tone and as quiet as I can get it without sacrificing too much performance. Suggestions?

I'm planning to have a cat put on to smooth things out and a different type of muffler. So, what type/brand of cat and muffler will do what I want? MagnaFlow? DynoMax? Other?

[bszopi]

I would say, add the cat first and then see what it sounds like. Which Flowmaster do you have, anyway?

[Superdave]

Aerochambers sound similar to Flowmasters but have less interior drone. They are still pretty loud without a cat though.

Dynomax superturbos flow very well and are quiet compared to a chambered muffler.

[19Cutlass94]

I replaced my Dynomax ultra-flo SS's with NAPA Quiet flow mufflers. I couldnt stand the Dynomax mufflers anymore. They were SO loud. and the sad part is I think the car runs better with these mufflers! haha. I know I didnt have ANY backpressure with the Dynomax's

[Canyonero]

Yeah, I think the lack of backpressure might be hurting me.

I don't know what flowmaster I have. I'll have to crawl under there and look, hopefully there is some way to tell...

[3400-95-Modified]

Darn backpressure myth...

Destroying a myth.



Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, 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. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

As far as identifying the muffler, flowmasters dont mark them with anything... so its rather impossible to figure out what it is, other than possibly measuring it and comparing the size to what they sell.

[johnnymossville]

^^^^ Very good explination. Everyone who has the ability to tune their engine should be able to develope a fuel map that will over come the lean condition present by improving exhaust flow. Engines are basically air pumps, which means that the induction and exhaust have to compliment each other. More air in means more air out, and vice versa. All that is left is to put the correct amount of fuel into the air to reach optimum performance through the correct air/fuel ratio.

[Superdave]

Flowmaster puts a part number on every muffler.. just match that up with them on their site to figure out what it is.

[3400-95-Modified]

They do? I didnt know that... I dont remember seeing one on my muffler.

[Superdave]

i've seen 50+ of them.. it's on the case sometimes near the logo, and sometimes on the ends.


i sold my stockpile though, i'll see if i still have any pics.

[gectek]

^^^^ Very good explination. Everyone who has the ability to tune their engine should be able to develope a fuel map that will over come the lean condition present by improving exhaust flow. Engines are basically air pumps, which means that the induction and exhaust have to compliment each other. More air in means more air out, and vice versa. All that is left is to put the correct amount of fuel into the air to reach optimum performance through the correct air/fuel ratio.

ummm...due to feedback controls, your engine shouldnt see a lean condition due to adding headers or a high flow exhaust system. if you pull more air through the engine, the O2 sensor will see more oxygen, think it is not getting enough fuel(artificial lean condition) and add more fuel...unless you are at WOT, where the engine runs on programmed commands not closed loop. and i dont know of anyone that CAN go wot everywhere, i know ive sure tried

[candychevy87]

i went with cheepos from advanced, the thrush turbo mufflers, they have a good sound, im using headers to straight pipes 4 feet later i have my mufflers, theyre really quiet at idle but at wot theyre not loud but they make a tone i find pleasing at 80 miles an hour

[Canyonero]

This is way old, but for the record I did revert to my factory y-pipe and used an universal magnaflow 2.5" cat to mate the stock y-pipe with the 3" flowmaster. The cat made it sound much better. Took away the raspyness at high RPMs and smoothed everything out. Years later and I've grown to like the flowmaster sound (with the cat).

[BillS]

I run a 3" with no CAT and a Magnaflow muffler. It was too aggressive at wide open throttle on its own but by adding a tip resonator it was tamed down to exactly where I wanted it. I used a Pacesetter twin tip resonator.

I agree with the advice that says that you should put the CAT in there first as that can affect the exhaust note a considerable amount.

[bob442]

Adding a resinator before the muffler will make a huge difference too. I have just a a 2 1/2" 18" long flow pro resinator on my 3400 right behind the CAT, its not that loud persay, but has a really good drone to it. and no backfiring, And as for any pops, its just has a bit of a "bababab" after heavy throttle, but that kinda went away after time for some reason.
Completely stock motor
2010:

http://s15.photobucket.com/albums/a351/bob442/?action=view&current=001-10.mp4

2008

http://s15.photobucket.com/albums/a351/bob442/?action=view&current=MOV00026.mp4