iDomN8U

Avoiding the "Fart" Can.

That leaves the following:
Q300 Single
70mm ASM
70mm T1R

I think that's it...

EVS is on the border

The Q300 I heard to me doesn't have a refined sound.. The others are big money.

s2jizzer

No engineering behind flow? Explain why certain exhausts make more power then others? Of course it's engineered, the way it sounds is also dependant on how it flows, the size of the pipe, and how restrictive or free flowing the exhaust is.

iDomN8U

Perhaps our definition of engineered are different. Their are minimal engineered exhaust for power (Gernby's).

Almost everyone else uses a perforated straight through muffler with minimal bends. They cookie cutter the same design. Some include a helmz resonator (already included with OEM) but this is for sound management not power. This isn't a bad thing however it's the base line standard.

Honestly exhaust do not make much power on this platform, the restrictions are in the Cat due to emissions (and even then thier very well built)

5hp means nothing.

kryptonite

All things considered without boost, 5hp is a good amount with this car

Either way to the point of getting one custom fabricated, get a quote and let us all know, curious to know what it would cost to do

A. Dos Santos

welp I don't think I'm gonna be able to do this for a while, my subaru $#!+box winterbeater is leaking both brake fluid and gas.

Why do I have such bad luck with brakes? 2/2 of my cars now have a leaking brake caliper from a failed seal on the piston.


if you're curious, I can still try to get a quote for you guys.

iDomN8U

I've looked into this and almost gave up trying to find 70mm straight through mufflers (oval, not round).

A. Dos Santos

how about 3" muffler?

s2jizzer

how about 3" muffler?
[/quote]
Dime a dozen

hawkman199

OK, thot I would weigh in here, as an exhaust system designer, albeit for gas turbines.

I am going to paraphrase Jack Kane, as he has already written on the subject. For the full article, go to: http://www.epi-eng.com/piston_engine...technology.htm



The computation of what actually goes on during an exhaust cycle is a highly complex problem in compressible fluid flow.

There are two separate components to the exhaust event. The first is the removal of exhaust gasses from the cylinder, which occurs as a pulse of hot gas exiting the cylinder and flowing down the header primary tube. The second is the (much faster) travel of the pressure wave in the port caused by the pressure spike which occurs when the exhaust valve opens, and the various reflections of that wave. Taking proper advantage of these pressure waves (component two) can produce dramatic improvements in clearing the cylinder (component one) and can strongly assist the inflow of fresh charge.

Considering component one, when the exhaust valve first opens in a 4-stroke piston engine, the in-cylinder pressure is still well above atmospheric. In a normally-aspirated spark ignition engine burning gasoline and operating at high BMEP, the pressure can be 7 bar or more, and the pressure in the exhaust port at the valve is somewhere near 1 bar (atmospheric). As the valve opens, the pressure differential across the rapidly-changing valve aperture (pressure ratio of approximately 7) starts exhaust gas flowing through the opening, and the outrush causes the pressure in the port (behind the valve) to increase rapidly, or "spike".

The instantaneous velocity of the exhaust gas flow at any point is determined by the pressure gradient and the cross-sectional area at that point. In the header, a smaller tube diameter will increase the velocity at a given RPM, which might enhance the pressure wave tuning (the second component) and can be beneficial with regard to inertia effects. However, if the diameter is too small, there will be flow losses and consequent pressure gradient increases which can offset any tuning gains. So the selection of proper tubing diameters is an important part of the design.
In the early part of the exhaust cycle, the pressure difference across the valve is high, so the instantaneous gas particle velocity through the small exhaust valve aperture is very high. Sometime past mid-exhaust stroke, the majority of the exhaust gas has left the cylinder. At that time, the valve aperture area is quite large and the cylinder pressure is approaching atmospheric, which causes the instantaneous particle velocity across the valve to be much lower. It is at that phase of the exhaust cycle where the second component becomes important.




The above figures shows traces of in-cylinder pressure (black), port pressure at the intake valve (light blue) and port pressure at the exhaust valve (red), taken from a simulation of a high BMEP engine operating near the optimum tuning point for both intake and exhaust.

The second component is the result of the pressure "spike" which occurs at EVO, shown by the peak in the red line in the above, just after EVO. That pressure spike, or pressure wave, moves down the pipe at the sum of the local sonic velocity plus the particle velocity of the gas flow. Whenever the pressure wave encounters a change in cross-sectional area of the pipe, a reflected pressure wave is generated, which travels in the opposite direction. If the change in area is increasing (a step, collector, the atmosphere), the sense of the reflected pressure wave (compression or expansion) is inverted. If the change in area is decreasing (the end of another port having a closed valve, or a turbocharger nozzle, for example), the sense of the reflected wave is not inverted. The amplitude of the reflected wave is primarily determined by the proportionate change in cross-sectional area (area ratio), but the amplitude is diminished in any case. For purposes of approximation, the particle velocity can be ignored because its effect is self-canceling during the round-trip of the wave. However, highly-accurate simulations must take it into account. These waves are sometimes called finite difference waves, because of the finite difference numerical modeling techniques used to calculate their propagation characteristics.

In the case of the currently-flowing header primary, the EVO-initiated positive pressure (compression) wave is reflected back as a negative pressure (expansion) wave. If the arrival of the reflected negative pressure wave back at the exhaust valve can be arranged to occur during the latter part of the exhaust cycle, the resulting lower pressure in the port will enhance the removal of exhaust gas from the cylinder, and will reduce the pressure in the cylinder so that when the intake valve opens, the low pressure in the cylinder begins moving fresh charge into the cylinder while the piston is slowing to a stop at TDC.

Note in the graph, how the cylinder pressure (black) and exhaust port (red) pressures go strongly negative from approximately mid-exhaust stroke to TDC). Note also how the second-order reflected positive pressure wave in the intake tract (light blue) reaches the back of the intake valve just before IVO, and works together with properly-timed exhaust negative pressures to begin moving fresh charge into the cylinder.
If, on the other hand, the negative exhaust pressure wave arrives a non-optimal time, its effects can be detrimental to the clearing of the cylinder and ingestion of fresh charge. A reflected positive wave during overlap (from a turbocharger nozzle, for example) can push a large amount of exhaust gas back into the cylinder and the intake system.

So, to summarize, in high performance engines, the ideal exhaust will help extract gases from the cylinder, on the exhaust stroke, by delivering a pulse of negative pressure just before the exhaust valve closes.

Non-turbo engines, and the S2000 is no exception, use an extractor manifold to separate the flow from each cylinder, so inter-cylinder interference is avoided. The velocity in each pipe is the same and when they come together at the collector, negative pressure waves assist in 'scavenging' the exhaust gases from the cylinder being evacuated.

Clear so far?

So what happens after the collector? You can have a catalytic converter, on the S2000 the stock cat is a high flow design, although there are other 'high flow' cats available, or you can install a 'test pipe' to pick up some horsepower and coincidentally cause your car to smell like the back-end of a farting horse. Following the cat or test pipe you can use any number of systems to get the exhaust gases to the back of the car, so you will not die from carbon monoxide poisoning.

The ideal system has the lowest back pressure possible. However, the law of diminishing returns kicks in, so there isn't much sense in going over 62mm dia. for NA engines. Having said that, the fewer the bends the better.

The other aspect of exhaust header design concerns heat. Mainly trying to get it away for the engine compartment. That is why the stock system has a bunch of carefully designed heat shields mounted. Don't take them off.

One of the things that has interested me in exhaust system design is the effect of the 'leaving dynamic head'. Is it possible to scavenge exhaust gas from the system by designing an exhaust tip specific for that purpose? Hmmm, worth a look. More to come.....

alSpeed2k

Hmmm, I wonder how much engineering actually does go into an exhaust? It's surprising that the exhaust companies don't have dyno sheets to show how much power is made (like K&N does for it's intake), whether the numbers are to believed or not, that's a different story, lol.