Perihal Ekzos
1. Panjang ekzos berkadar songsang dgn RPM. Lg panjg ekzos,bgs kt low rpm.ekzos pendek bgs kat high rpm.
2. ekjos 2-lejang de 5 component bermula dari exhaust port iaitu header,diffuser,baffle mid,baffle end,stinger.pastu bru g ke silencer.
3. header=manifold=tengkok, perot ekjos= baffle mid, corong = baffle end. (dari segi istilah kampung dengan teknikal)
4. corong2 utk wt back pressure.kiranye,asap ekjos de yg kua ke environment dan de yg msk blk.fungsi back pressure,kasi high compression kt combustion chamber.
5. diffuser plk de byk angle & diameter tersendiri.multistage diffuser. diffuser nk kasi flow ekjos selaju yg mgkn.
Perbezaan Ekzos 4-lejang dan 2 lejang
As with a two-stroke expansion chamber, a four-stroke exhaust system is tuned to produce the optimum powerband.
The major elements of pipe design are:
(1) head pipe length,
(2) head pipe diameter,
(3) overall tuned length,
(3) taper of S-bends,
(4) diameter of the muffler core and
(5) length of the muffler.
Unlike Formula 1 or road racing exhaust pipes, a four-stroke pipe has to deliver a broad and usable powerband--instead of maximum horsepower.
In the future, expect to see tapered head pipes, steps, stamped shapes and exotic metals (like Inconel) being used to deliver more low-end, a broader mid and extra top.
Other tips:
* By reducing the exhaust back pressure, engine power is increased in four-stroke engines
* By reducing the amount of heat from the exhaust being lost into the underbonnet area. This reduces the underbonnet temperature and consequently lowers the intake manifold temperature, increasing power. This also has positive side effect of preventing heat-sensitive components from being damaged. Furthermore, keeping the heat in the exhaust gases speeds these up, therefore reducing back pressure as well.
Kaitan Ekzos 2stroke dan 4stroke
Sebenarnya kaitan dia ada pada emission control..
sebab ekzos stock di buat agar mematuhi emission control.. so akan ada restrict... kat sini hp jd rendah sedikit...
bg 2 stroke, ekzos merupakan salah satu part of engine...
dia akan kekalkan back pressure supaya ketika sedutan/kuasa, campuran minyak tak trus terkuar semua ke ekzos...
bg 4 stroke... agak complicated...
sebab perlu disesuaikan dengan cam, valve, port, comp, bending, sizing piping...
ekzos terlalu lawas akan watkan enjin ringan pada hi rpm tp lemah pada low rpm.. sebab takde pressure yang sesuai ketika overlap cam berlaku..tambah2 pakai hi cam beroverlap besar...
antara sebab ekzos 4 stroke di cipta dengan cone di dalam adalah utk mengekalkan back pressure...
ekzos terlalu lawas pun bila hi rpm, campuran minyak akan terkuar sebab dah jd vacum dalam ekzos watkan lost power n takde top speed
Analogi
1.back pressure = tekanan udara di luar ekzos
2. tekanan gas ekzos
utk 4-stroke,
back pressure > tekanan gas ekzos = less power pada low RPM, tapi power pada High RPM. sesuai utk high power engine.
back pressure < tekanan gas ekzos = more power pada low & mid RPM tapi agak kurang sikit pada High RPM. sesuai utk kegunaan harian.
mcm mana kawal tekanan gas ekzos yg keluar ?
ikut header design
contoh,
header 4-1 = flow gas ekzos dari 4 manifold terus direct keluar ke ekzos. low RPM, takde power sbb terlalu lawas, tapi high RPM baru dtg power nya sbb tekanan gas ekzos yg keluar lebih besar dari back pressure dan gas ekzos keluar tanpa ada halangan (lawas).
header 4-2-1 = ekzos flow yg keluar dari 4 bijik manifold, dikumpul masuk ke dalam 2 tabung kecik...bertujuan utk meningkatkan pressure ekzos yg keluar sebelum ditumpukan keluar ke ekzos..pada low RPM, tekanan gas ekzos sememangnya lebih tinggi dari back pressure menjadikannya power pada takat RPM tsebut. tapi, bila High RPM, agak suffer sbb flow gas ekzos terhalang menjadikan powernya mendatar.
Stepped Header
The stepped header causes the negative wave decrease pressure as it hits progressively smaller cross sections and that's where the benefit comes from the stepped headers.
Exhaust port shape and valve size are crucial for determining the optimum size differential and location ofsteps in a header pipe.
A stepped header won't necessarily make more power than a non-stepped pipe, but it can broaden the engine's torque curve by widening the scavenging wave's effect, which increases the time of negative depression.
This can result in a win-win situation: High torque at low rpm while maintaining high horsepower at high rpm.
Stepped headers are most beneficial when used on large-displacement and/or high-rpm engines.
Key exhaust system considerations include pipe diameter and length.
Both pipe variables should be optimized based on engine displacement, rpm band, cam timing, and application.
If a collector is used, its diameter and length also must be considered. Bike weight, gear ratios, and the number of gears along with the application also enter into the equation for optimum exhaust design.
Header diameter (inside diameter) is typically the most important factor in exhaust system design because it sets the torque curve.
Increasing diameter generally improves top-end power at the expense of low-end torque.
Changing pipe length will move the torque curve either up or down the rpm scale.
A shorter pipe favors top-end horsepower while a longer pipe caters toward low-end torque.
Straight pipes typically improve power above roughly 4,000 rpm, which is great for an engine that never drops below this rpm. However, at low rpm, straight pipes generally create big dips in the torque curve, reduce throttle response, and make jetting difficult.
Info diambil dari link dibawah.Lagi info penuh:
http://www.hotbikeweb.com/tech/0805_hbkp_exhaust_systems/index.html
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