I don't purport to hold even a moderate knowledge of exhaust system design theories, but through my reading I've come to learn some basic concepts which seem to be widely accepted. These include the importance of cylinder pairing, gas velocity, and eliminating reversion.

Over the years, there have been a number of posts to the effect of, "Where can I get a phat dual exhaust for my Teg y0?", which have been met with obvious and deserved responses. The idea of a true dual exhaust system is just not a serious concept for our cars (though it does show up on motorcycles).

That being said, I've done some thinking and applied my very basic understanding to the actual theory behind it. Mainly, this came about as a result of the monotony that seems to be sweeping over H-T and the ITR forum in not-so-recent months. I reason that, even if the ideas I present are not theoretically sound, they will at least have introduced an opportunity for discussion and a concept which I don't think has ever received much attention (and who knows, perhaps for good reason).

As you've probably guessed, the idea I'm referring to is the concept of a true dual-exhaust setup on a high-reving, small-displacement 4 cylinder. For the sake of the initial discussion, lets not consider the weight penalties of such a system, and simply look at any possibe potential for power-getting (in the words of Fujitsubo).

The idea I've put together in my head is a header similar to the long-tube 4-2-1's, but ending in two small collectors (effectively making two 2-1 headers). These collectors would have a combined area greater than a single 2.5", but would help maintain velocity and scavenging because of their smaller individual size (at least that's what my limited understanding of fluid dynamics tells me). Each would then be paired to an individual exhaust system that would again be larger in combined area, but smaller in individual, with the same intended benefits. Obviously there would be packaging and routing issues to address (and there might simply be no simple solution for some of them), but the basic concept is as I've presented it.

I'd be interested in hearing anyone's thoughts or contributions on this. (Now that I think about it, I think I may have suggested something like this a long while back, but don't think it ever received any attention.)

 

From Michael Delaney aka twan (on other message boards)
"depends on the total cross sectional area of the 2 tubes. If they add up to be the correct total area for the hp goal, then you're fine. But if they have, like in most cases you see out there with beginners choosing the wrong size dual exhausts purely for show, too much area then you lose a lot of energy from the exhaust pulse and the flow speed just dies. it would be like getting a 3 in. OD exhaust for an engine package that needed 2.25 in. OD in a single exhaust situation. If the 2 tubes are sized right (small enough) as you add up the 2 tube's cross sectional area, then you may be ok.

exhausts with cross over tubing like on a dual exhaust, if sized correctly, will deepen the exhaust tone and give you a little more low end torque, as seen in the new Viper."

i think it'd be a cool project to have somebody go ahead and do this and post results. Hell...if i had the money, i would. I would say make the exhaust 1.25in each...

 

here's another great post by MD about the velocity of the exhaust fumes...

Now you are getting to next level of knowledge about exhaust gas properties. Think about what merging the energy of individual exhaust gas pulses do. In physics, we talk about harmonics. This is the sound properties of a gas. We look at the way the exhaust gas behaves as a sound-pressure wave. A wave in physics has a height that it oscillates at (Amplitude) and the number of times this up and down oscillation repeats itself (Frequency).

When you merge the energy of 2 separate pressure waves , this coupling at the secondaries boosts the level energy together..amplifies the amplitude. Then you merge their energy again at the main collector and this "boosts" the energy again.

The advantage is you get a nice spread of the powerband. The exhaust gas speed increases. Without merge collectors or pairing, the power would occur very late in the rpm range and not have what we call driveability.

Notice that the race-only side exit headers in my Bseries header articles exit at the side beside the radiator, just in front of the passenger side front wheel. They don't need an exhaust muffler. Yet the header primaries are merged into secondaries and then to a collector (in a 4-2-1) or into a main collector (in a 4-1). Merging the main primary tubes pumps up the exhaust speed.

From a practical standpoint, even if it was not an advantage to merge the tubes, 4 cylindrical mufflers would be awefully expensive.

 

.....I have often wondered what would happen if I removed the secondary/ collector section off of my hytech header.

I guess maybe one of these days I'll dyno it and see!

Prolly lose power, but it'll be interesting (and sound weird)!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JiggyKooAndy &raquo;</TD></TR><TR><TD CLASS="quote">here's another great post by MD about the velocity of the exhaust fumes...

Now you are getting to next level of knowledge about exhaust gas properties. Think about what merging the energy of individual exhaust gas pulses do. In physics, we talk about harmonics. This is the sound properties of a gas. We look at the way the exhaust gas behaves as a sound-pressure wave. A wave in physics has a height that it oscillates at (Amplitude) and the number of times this up and down oscillation repeats itself (Frequency).

When you merge the energy of 2 separate pressure waves , this coupling at the secondaries boosts the level energy together..amplifies the amplitude. Then you merge their energy again at the main collector and this "boosts" the energy again.

The advantage is you get a nice spread of the powerband. The exhaust gas speed increases. Without merge collectors or pairing, the power would occur very late in the rpm range and not have what we call driveability.

Notice that the race-only side exit headers in my Bseries header articles exit at the side beside the radiator, just in front of the passenger side front wheel. They don't need an exhaust muffler. Yet the header primaries are merged into secondaries and then to a collector (in a 4-2-1) or into a main collector (in a 4-1). Merging the main primary tubes pumps up the exhaust speed.

From a practical standpoint, even if it was not an advantage to merge the tubes, 4 cylindrical mufflers would be awefully expensive.</TD></TR></TABLE>


Be very careful, here not all frequencies and amplitudes, the key to exhaust tuning is the phase of the waves themselves. This is the basic theory behing hemlohz tuning. The waves in the exhaust system are setup to devolp a low pressure area just past the exhaust valves therefore increasing the delta pressure at that point aiding in getting the velocity of the gas up. This calculation is slightly complicated and relys on many "givens"

The actually waveform anaylsis of exhaust gas is simply not possible as far as I know. (Although testing can be done, calculating and getting the correct results can only be approximated either with the WAVE computer program or the physical calculation of Helmohz
(which by the way I am spelling incorrectly maybe someone can pitch in with the correct spelling)

The other issue with dual exhaust is slightly less intuitive. The major way to propel gas out the exhaust system is the heat of the gas itself. This is transformed into Kinetic engery KE= 1/2 M v^2
If you put into two exhausts the total exhaust tubing area will be greater allowing for more heat to be disipated as the gas exits, lowering the efficiency of the exhaust system hence killing power.
This isnt an issue for large displacement engines which exit a larger volume of exhaust flow.

This is at least how I percieve this, but I am in no means an exhaust expert

~Matt R

 

this is an interesting topic. Obviously the idea holds some merit because of the number of motorcycle manufacturers implementing true dual exhaust systems on thier newest bikes (see Honda CBR, Ducati Supersport, etc). These are, like our beloved ITR's, very small displacement engines, yet they still go through the trouble to design a dual system - this leads me to believe that there must be some benefit over a convention 4-1 collector system.
Unfortunately, creating true dual exhaust system for a car like the integra would be difficult at best, because of the lack of space under the car. I am suprised that no one has tried anything like this before - maybe SMSP will chime in and educate us

&lt;=== would love to hear what a type R with true dual exhaust would sound like

 

 

very nice...price? how does it fit under the car? except...it doesn't look quite like a dual exhuast. it looks like a 2-1-2-1 header (if that makes sense lol).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Philly_NBP_R &raquo;</TD></TR><TR><TD CLASS="quote">maybe SMSP will chime in and educate us

&lt;=== would love to hear what a type R with true dual exhaust would sound like</TD></TR></TABLE>

Yes, me 2!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Philly_NBP_R &raquo;</TD></TR><TR><TD CLASS="quote">this is an interesting topic. Obviously the idea holds some merit because of the number of motorcycle manufacturers implementing true dual exhaust systems on thier newest bikes (see Honda CBR, Ducati Supersport, etc). These are, like our beloved ITR's, very small displacement engines, yet they still go through the trouble to design a dual system - this leads me to believe that there must be some benefit over a convention 4-1 collector system. </TD></TR></TABLE>

The CBR uses a 4-1 style exhaust as do all of the 600 (and most liter class) bikes. And the Ducati is a v twin where dual exhaust is more common (ducati, honda superhawk, H-D). True the CBR1100XX and Suzuki Hayabusa1300 use a dual muffler design, but I think that is more for style than performance. Those bikes already have enought hp and a few more lbs aren't gonna hurt.

X-pipes (similar to what SMSP has posted) have been used in domestives for years.