carguy123 said:
Let's talk exhaust note tuning. All the big boys do it, well at least Maclaren does cause I saw the guy at work in a Youtube video.
I recognize that there are basic differences in sound between engines, for instance the sound varies according to the number of cylinders. To me one of the prettiest sounds on the automotive planet is a BMW V10 M5 when it is on song. I'm working with a V6 so I recognize I can't get that sound, but can I tune the exhaust note to get something that might give me part of that sound?
I'm also wanting my exhaust to be on the quiet side for around town driving like the M5. In otherwords, I want it all.
I realize that a lot of getting a pretty exhaust note is subjective and will entail quite a bit of trial and error, but I'd like to minimize the error part some if I can. I'm also hoping that some of what I learn here can also be applied to my S2000. I realize it's apples to oranges in sound, but some of the techniques or benefits won't be.
#1 what effect does exhaust material have on the sound? eg. is Ti inherently higher pitched than regular old, thick steel exhaust tubing?
#2 An X or H pipe helps quieten the exhaust note plus tends to smooth out the sound. The X is better for power, but if an H is all you can fit would a resonator or glass pack type of muffler within the H help any or affect it at all?
#3 Does header length or material matter much in the overall scheme of things?
#4 Since Hot gases take up more room than cool gases I'm guessing that a properly designed exhaust system would have tail pipe volume diminishing the closer you get to the tail pipe to help keep the gas velocity up to help with scavenging and maintain torque (no you do not need back pressure to maintain torque).
And speaking of exhaust tubing sizes this article about how to build an exhaust system to work Laguna Seca sound limits states that 2 1/2" tubing was the max you could use to get around the noise limits - well along with a number of other things.
http://www.norcal-saac.org/track/doc/soundadvice.html
#5 how much does a turbo affect the sound level, sound quality & sound tone?
#6 How about Anti-Reversion? From what I can read that's actually a thing. BUT they say an abrupt change in diameter is needed and yet everything else I read says a gradual change in diameter is better for flow - think more like an expansion chamber of a 2 cycle engine as a comparison.
I know that the further from the tail pipe you put the muffler the smoother the sound and quieter it will be. That used to be where all mufflers were placed, but the catalytic converters are now mounted there and look at what they have to do to attenuate the sound with those tailpipe mufflers today.
How much do the sound canceling mufflers really affect power over straight through designs? Many of the larger body type of mufflers use strategically placed and sized pieces of metal to cancel the sound waves. They also tend to have flow patterns that go all over the place. I'm guessing the circuitous exhaust route itself is the major disrupter of the sound waves.
#1. Very little. It has a much greater effect in the frequency ranges at which the tubing resonates, but you'll never get there. At 5000 rpms, a V6 is pulsing around 250Hz. Resonance frequencies for metal tubing are likely in the thousands of Hz. Even in things like brass instruments like trumpets and trombones where they can play near the tubing's resonant frequency, the type of metal used (brass, silver, chrome steel, etc) make minimal timbre changes in the sound of the instrument. Of course, a trumpet player will describe it as brighter or softer, but to the lay person they all sound the same.
#2. I usually tell folks to leave Xs and Hs to the manufacturer because they have an R&D budget. X pipes are less sensitive to placement than H pipes, but both only really have their biggest benefits when properly placed. Do it for sound, but I don't feel the need to chase down the last 3 hp and 2 torques. Having said that, I do like the more even sound that a crossover provides. A similar effect can be accomplished with a 2-1 muffler.
#3. Header length and diameter (to me) are a fixed entity. The length should be optimized for the maximum scavenging effect and the diameter should be matched to the powerband. Deviation from that optimal combination could cost power or torque in chasing the sound you want. Having said that, you can scoot your header dimensions a bit each way without much effect. Larger diameters will be louder, shorter length will be choppier
#4. You are correct in your assumption. Many mufflers have smaller diameter outputs than inputs for this reason.
#5. Turbos (as a guideline) add 1/3 of a muffler. That is a highly subjective thing, though. Do they add 1/3 of a stock muffler, or 1/3 of a race bullet muffler? Turbos also tend to mix things up. They combine pulses for a smoother exhaust note.
#6. Airflow hates change. If you have a nice, laminar flow of a fluid or gas in a tube and change the tube's direction or diameter, it is forced to change and requires a change of energy intensity. Anti reversion may help on really gnarly engines with a ton of valve overlap, but on a relatively mild engine I don't see the need. It may assist torque lower in the RPMs, but once you're at WOT and getting to the torque peak, reversion is the least of your worries on a well-tuned exhaust.
Placement of the muffler closer to the tailpipe does make things quieter, but it also greatly helps eliminate interior drone. When you put the muffler farther forward, there is more length of tubing behind it to re-establish resonance. This in turn can create standing waves of sound that cause the body panels to vibrate sympathetically. Back to the trumpet analogy, this is why a trumpet mute goes on the end, not at the player's mouth. You want to generate the tone you want at the end which gives less opportunity for the resonances to do their own thing.
Some engines will just never sound good and some will never sound bad. One of the finest exhaust notes (as has been pointed out) is that BMW V10. One of the worst in the world is the Ford Triton V10. There are so many hundreds of factors which create the exhaust note, so getting the sound you want would be different for every engine. Think of the 350/370Z cars with a V6. They growl like a bobcat and sound incredible. You could duplicate that entire system on a 3.8L Buick and it would sound like trash. In the trumpet analogy, it doesn't matter what the qualities of the instrument are if the lips playing it aren't giving the mouthpiece the same type of vibrations.
Cam plays a big role. Exhaust ramp speed, valve overlap, duration, LSA. One of the tricks my cam grinder does to make a cam sound "bigger" is to grind a more aggressive EVO ramp to make more of a "pop" of exhaust gas when it opens. Exhaust port shape is a big one. Manifold design (equal length, tuned, log) plays a lot. One of the biggest things, though is firing order. When you get the exhaust pulses is a pretty important thing in the sound.
OEMs play with big budgets to get it right. In my garage, I use trial and error. I make up the system with no tailpipe and then hold a few different mufflers up to it to get an idea.
In general, glasspack style mufflers are not your friend when it comes to power. There are some that would be fine, but you'll notice that they don't get any larger inside, and usually get smaller. They don't seem to excel at canceling noise OR flow. I wouldn't hesitate to use them as a resonator as long as I sized them accordingly. Race bullets are designed for max flow and the bare minimum of sound canceling. I do like the idea of the open-chamber mufflers that attempt to cancel sound waves by reflecting them around, but many of them sound pretty raspy to me. Many of the performance aftermarket offerings use large, adequately-sized passages inside sourrounded by a sound deadening material. These tend to attenuate higher frequencies better and don't restrict much flow.
Bigger diameter is usually louder. Longer is usually quieter.
I say, try a bunch and see what you think.
