Today I'd like to briefly address some of the most elementary modification issues

- May 25, 2018 -

First of all, why change the exhaust?

I think more than 80 percent of the fans are to let the civil car out that moving sound waves, have a domineering dynamic appearance, just decided to take out a wallet, out of thousands, buy!~ ~

In fact, for civil refitting, competition, these two crucial!This is also the manufacturer to make a beautiful plating tail, beautiful design of the logo on the tail;Design a variety of bilateral double out, bilateral four out of the exhaust reasons, as well as the middle out of the exhaust reasons.

What are the modification methods:

Exhaust modification, that is, the original factory's exhaust to become free.There are several ways: 1. Change the muffler.2. Muffler structure change.3. Change the pipe diameter. 4. Remove the three-way catalytic converter.


The tail-end mufflers of the modified exhaust are small and obvious.And generally change the middle section, that is, the middle section of the exhaust muffler removed, into a straight through pipe.


Muffler structure, the original factory is a pipe to the complex metal asbestos noise reduction damping material, full noise reduction, from the other end of the export, so the original car exhaust very quiet.Refitted exhaust generally adopts a straight pipe through the past, the pipe wall is punched very porous, the outside of the hole is the silencing material, only indirect part of the silencing.


Increase the pipe diameter, obviously.


Take out three dollars.The ternary structure is a ceramic honeycomb net. In a jar, there is a ceramic structure several tens of centimeters long.These ceramics are structured with catalysts to convert harmful gases.This kind of structure is very obstructive to the exhaust, which is also to increase the contact area between the exhaust gas and catalyst and increase the conversion efficiency.Get rid of 3 yuan to change to pass through directly, this kind of honeycomb structure that close up dead did not have, exhaust can say is incomparable unobstructed, but incomparable not environmental protection!!

Whether it's 1, 2, 3, or 4, it's all about lowering the "exhaust back pressure," which is actually the name of the exhaust resistance.It's a measurement.When the back pressure of the exhaust is reduced, the sound of the exhaust will be louder.Because the function of the exhaust itself is to reduce vibration, the exhaust is unobstructed, that is, the damping function is weak, the sound is naturally loud (the sound is the vibration of the atmosphere).

(here I want to say, I highly recommend no. 4 refit, that is, no. 3 yuan for demolition.I have a lot of friends around me who do this.But!!!!!Extreme irresponsibility for the environment!!A golf 6 without a $3 will emit about 300 times as much pollution as a normal euro5 golf 6.You can think of it, you don't have three dollars alone, which is equivalent to 300 cars driving on the road!How are you?!!!!?

How does the change of exhaust improve performance?

The short answer, the exhaust is smooth, the power is good!This is the only way many JS, and many beginners, can say it

Or more advanced JS would say, is the waste discharge flow in the cylinder, the vent from the clean, good combustion, power will be strong ~ ~ actually is only one-sided feelings, not science.

The reduction of exhaust back pressure, in the end why the performance of the car will change?

First of all, for the four-stroke engine, it is divided into: inlet, compression, ignition work, exhaust ~ four stroke.Driven by the camshaft, the inlet valve is first opened, and fresh air is sucked in from the inlet valve as the cylinder descends.Then close the intake valve and start the process of compression and ignition. Finally, the exhaust valve opens and the cylinder goes up. The exhaust gas is discharged from the exhaust valve and a cycle is completed.Then the intake valve opens again and the next cycle begins.This is the simplest and most rudimentary description of the work of an engine.

It is important to introduce the concept of valve overlap.It must be designed in order to ensure adequate intake of air, otherwise the engine will have inadequate intake, low combustion efficiency and low torsion.The meaning of this valve overlap, it is in the final step in a cycle, the discharge of waste gas process has not yet been completed, that is to say, the exhaust process of piston is not up to the top dead center (top), the inlet valve is opened.This allows the intake valve to open early, allowing the cylinder to reach the upper stop point immediately after the first time to start inhalation, to ensure that the intake valve is open, ready.This inlet valve opens early and is open with the exhaust valve, which is called valve overlap.

Valve overlap must, and will lead to the exhaust process of piston is close to the top, finally the one mouthful exhaust, be with out the exhaust valve discharge at the same time, there is also a part of out of the inlet valve and enter the inlet (this is also why idle dirty easily throttle).In this way, the next intake process, in fact, just the last one out of the exhaust gas, back to the inhalation of fresh air.

One might say, well, why is it designed this way?Isn't it counterproductive to inhale a bit of exhaust?Not really.Valve overlapping is necessary.First we talk about the role of valve overlap, for low speed engine combustion, due to the high cylinder compression mixture speed is slow, so the ignition moment, mixture temperature is high enough, it will lead to insufficient combustion.It can be said that the general gasoline engine speed under 3000 is not sufficient combustion, the higher the combustion temperature, the better the combustion.What does underburning mean? Yes, it means that the polycarbon in gasoline is not perfectly converted to carbon dioxide or carbon monoxide.There's still energy that's not released, it's not completely burnt.These unfinished polycarbon chains, these high carbon components, are heavy and dense in the exhaust gas.That is to say, in the exhaust process, the last one of the main components of the exhaust gas is this dense, incomplete disconnect of all the carbon chain

So in low speed range, the benefits of valve overlap is not completely release energy of carbon molecules, can once again be lit by the next burning, and compared with the fresh gas molecules, the last remaining carbon molecules more easily ignited, burning less because they carbon chain, small molecules.The advantage is obvious, it is low speed fuel economy!!Because what does not burn can be used again!And the power is strong (torque is strong), because this part of the exhaust gas is better lit!

Conversely, high speed, piston compression valve quickly, before the light mixture temperature is very high, so high combustion efficiency, after high speed 3000 RPM, the combustion efficiency is generally very good, so only a few incomplete combustion in the exhaust gas carbon molecules.So that's when the valve overlaps.Due to sufficient combustion, the reinhaled exhaust becomes a non-combustible drag, which reduces the power of high speed and reduces the combustion efficiency.

This is the effect of valve overlapping on low and high speed, and like many contradictory factors on the car, this is also a difficulty in design.

At the same time, you can see VVTI, which is the technical effect of variable valve timing!Variable timing valve technology, which can change the traditional fixed mechanical camshaft drive inlet valve principle.Increase valve overlap at low speed so that the inlet valve opens more early, and more exhaust gas is sucked back again after discharging into the inlet, reducing low speed fuel consumption and improving low torque.At the same time, when the speed is high, the inlet valve will be opened later to reduce valve overlap, so that less exhaust gas will be sucked back again and the power of high speed will be increased.It's a good technique.

However, Volkswagen's medium and low-end cars, which have been reluctant to use the vvvti, which is widely spread in Japanese cars, may be the design concept and good road conditions in Germany, which are generally the reasons for driving at high and medium speed.However, the natural intake engines of German high-end cars are generally equipped with similar technical functions.

Many Japanese cars have vvvti, CVVTI and so on, which is one of the reasons why Japanese cars save oil at low speed besides being light in weight.

Return to the modified exhaust, after the exhaust modification, the reduction is the exhaust back pressure.The exhaust back pressure has a great influence on the valve overlapping effect.This can be simply understood as, the exhaust back pressure is small, equivalent to the exhaust gas can be more easily pressed into the exhaust duct, so it will reduce the valve overlapping effect.More gas is being pumped out of the exhaust and less is being pumped into the inlet during the crossover.This is equivalent to the valve overlapping range reduction!The effect is the same as the above analysis of the principle of valve overlap.Low speed combustion, low torsion, low speed fuel consumption increased.The result is high speed combustion, high speed power torque increase.

So retrofit exhaust has these two contradictions!The effect of grounding at the root or on the principle of valve overlap.

Therefore, the modified exhaust, with beautiful sound and attractive appearance, is not 100% good for performance.A lot of people change it for appearance and sound, and so do I.When it comes to performance, the above conclusions and principles should be known to be true amateur refit enthusiasts.

For high speed power cars, or demanding, extreme aggressive drivers, under 3000 will only appear in 1 gear!In the future, the red line shift, forced down gear, so the speed of each gear will not fall below 3000.So for them, the lower the exhaust pressure is, the better!Three dollars removed, tube diameter changed to 3 inches, 3.5 inches, middle muffler removed, end muffler reduced or simply removed.

Should I change the end, or the middle end, or the whole paragraph?

1. Sound problem: the modification of exhaust and the increase of sound generally show the trend of getting closer to the engine, the greater the sound change and the greater the volume increase.My experience is to rule out the final silencer's determination of tone color.Generally only change late exhaust, than the original car exhaust volume, image is about three times (here don't have to sound pressure, namely decibel to measure, because not enough image), three times for the average driver, is feeling a little down, but is not big.

After replacing the middle tail exhaust, the sound can be expanded to only replace the tail exhaust system twice, which is equal to about 6 times of the original car.For the average person, this volume is already very suspicious, the morning or evening quiet community, will be in the building vaguely heard the sound of the downstairs such as the reloading car.

If you are further removing the ternary catalysis, or replacing the expensive racing ternary, the sound pressure will increase more dramatically to two to three times that of replacing the middle tail exhaust.Reach similar to the original car more than 10 times the volume feeling!It's quite loud

In the background noise of the road, you can let yourself and other drivers, as well as roadside pedestrians, clearly hear your roar!Basically when the city road big foot accelerator, apart 20 meters can hear the sound.

Depending on the individual's tolerance to the sound, and preferences, it is modified according to personal judgment.

2. Performance problem: the effect of exhaust pressure on low speed and high speed has been mentioned above, and the concept of valve overlapping has also been introduced

Remember that as long as the exhaust sound is loud, it will be under pressure!Low pressure means low oil consumption and low torsion difference.High speed power and torque are also improved.This is an inescapable problem.

What kind of exhaust is good:

For normal passive exhaust.Look good!Stainless steel for materials!Welding integrity without defect!Combine with the original car firmly!Voice load personal preferences!Even if it's a good exhaust!As for performance, or that sentence, exhaust is very common technology!!High sound, low pressure, high speed performance, high pressure, low speed performance

For high - grade exhaust, it is divided into advanced material and advanced technology.

Material advanced: some brands use high-grade titanium alloy to make, belong to luxury goods absolutely.The visible end of the mouth is also worth investing in, the invisible part, that is really the choice of the beaded lovers ~~

Advanced technology: high - grade customized modified exhaust, can be installed in the car electrical control, or according to the engine speed of automatic adjustable exhaust air valve.Exhaust means, such as a bilateral and each side two mouth (and sound attenuation on the edge of each package, are the real two pipes, rather than the most common exhaust, only at the exit is divided into two mouth).It will be at low speed, through the electrical or hydraulic control valve, close a tail port, equal to a double out.This increases the exhaust pressure, enhances the valve overlapping effect, enhances the low twist, reduces the fuel consumption and the noise.As the speed increases, gradually open the valve, so that the pressure is reduced, reduce the valve overlapping effect, improve the high speed combustion efficiency and maximum power!Achieve dual exhaust!This kind of exhaust is required to be customized for each car, testing on the DYNO machine, can be said to be expensive high-end products!Prices generally range from 4W to 10W.

A good exhaust, I think ordinary people and domestic market conditions, can only do passive exhaust modification.It is to take doctrine commonly, no matter be homebred, still be imported, take pack namely.In fact, exhaust is the most free thing, can buy their own pipe welded, 304 stainless steel pipe, the price is very cheap, 2.5 ", 3 "pipe, elbow, some iron rods for support, buy and various shapes of exhaust nozzle.Find your own suitable size muffler, imported universal end muffler, solder it yourself, make it yourself ~ it's really free to match the style and style you want.The only problem is time-consuming, laborious, sometimes repetitive changes, welding!I have to design and build.The cost is very cheap, you can make the style you want, the thickness, the performance is not a problem.

In the same sentence, the exhaust is the problem of the stressed and silenced resonant tones of the tail, nothing new.

I still stick to the consistent point of view: when you understand from the principle, why should be refitted, why can have the effect after refitting, after having own understanding and judgment basis.Refit again, in the purchase!Is the wisest choice, will not go astray, spend the wrong money, into the wrong!

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