The Big EXHAUST Thread
Ok, a cars Exhaust system, Like a Induction kit are one of the easiest things to change on a car if you are looking to add some performance and extra noise to your car. When you ask most people what their first mod was they will either say Airfilter or Exhaust
On the back of my Big INDUCTION Thread I thought Id have a go at Exhausts.
Before I start Id like to point out that different people have different views on what exhaust perform and how they perform. I claim to be No expert but hope this thread inlightens people who dont know where to begin.
Exhausts
Why do I need a Exhaust?
Ok, if you didnt have any exhaust system at all, exhaust gases would exit striaght from the head (where the air and fuel are burnt to make an explosion or combustion) and would soon fill the engine bay with harmfull gases not to mention the cabin of the car, the engine would run very poorly and would the car sound like a Tank! A exhaust system is made up of different componts that are all designed to take exhaust gases from your engine then filter them, reduce the noise from the explosions that create the gases and then throw them out the back of the car so that the process can repeat itself and the car can not just perform well but simply work in the first place.
What Parts make up a Exhaust system?
Right to understand how to improve something first you must understand how it is made up in the first place and how it works. Modern exhaust systems are made up of the following items:
1) The Exhaust Manifold - This is connected to the head and is feed from the cyclinders, normaly one per cyclinder.
2) The Cat - This is a new addition to a exhausts system all cars after 1994 have had to have a cat to pass an emission test at a MoT, it is a box with special materials to filter out harmfull elements in the exhaust gases.
3) Centre Section - Normally this links the Cat or Manifold to the Back Box and has a Silincer in it to reduce noise levels.
4) Back Box - This is the final part of the exhaust system and is the bit that is on show, it is basically a Siliencer to reduce the noise leve and has a tailpipe so the gases can escape to atmosphere.
Will a Exhaust increase Performance?
The
RIGHT exhaust for your car Will improve performance, the
WRONG exhaust or a
BADLY Designed exhaust could lose you performance, a damaged or blowing exhaust will also effect the way the exhaust works and will lose performance. A performance or Sports exhaust normaly has less dense siliencers to improve gasflow there by improving the performance of a engine.
The factory exhaust was designed to meet many qualitys manily costs as all cars barring Super Super cars like a Zonda are made to a strick Budget to keep costs down, after all would you spend £20,000 on a Saxo? No, I didnt think so thats why all cars are built to a budget. A factory exhaust has to last out a warrenty, be quiet, be able to pass a emissions test at MoT time and still offer the right kind of performance to match the cars looks and claimed performance figures. Aftermarket Sports Exhausts are designed to be an improvement on a standard to mildly tuned car over the factory exhaust item.
IF you ever intend to look at Throttle Bodies, Turbochargers or Superchargers or anyother high power mods you should look to a more specailist exhaust system rather than a off the shelf system, as it wasnt designed for that much extra performance over standard.
What Type of Exhaust can I, do I buy?
Before I go into what kind of exhaust there are and what
will and
wont do in terms of improving performance, Id like to make one thing clear:
There is NO single One exhaust on the market today that is Proven to be the 'Best of the Best' for a Standard or Mildly Tuned Saxo. There are alot of good performing sports exhausts on the market, but I am not here to promote or steer you towards one brand.
Ok I shall start with the Back box and work my way towards the front.
Back Box
The Back box is a easy item to change and will have the greatest effect on changing the Looks of your car as the change of tailipipe size normally for something slightly bigger will really stand out over the factory back box. NO back box will effect performance in anyway at all as this is not where the biggest restrictions are to be found in your exhaust system. A sports back box can cost anywhere between £80-£150+ depending on type, brand and size
The Cat back System
The Cat back system is the next in the line of upgrading your factory system, this offers a real gain opposed to the back box as a decent sports exhaust should have better silincers to improve gaseflow and hence changing the exhaust note and performance. All 'off the shelf' Cat back systems are MoT legal as they keep the Cat in the system and shouldnt be so loud as to fail a MoT. A Cat back exhaust can cost anywhere between £150-£300+ depending on type, brand and materials.
Straight Through Centre Section
This is basically what it says it is, a centre section with the siliencer removed. This will do two things, greatly improve gasflow and increase noise levels. This is totally legal, as older cars may have only had a single siliencer but as laws and MoTs have changed over the years cars have had to be quiter, so most cars will come with at least one siliencer as well as the back box which is a siliencer. These can cost anywhere between £50-£100 depending on brand and material
Sports Cats and DeCats
When the Cat comes into question in terms of condition or performance you have two options, you can either by a 'High Flow Sports Cat' which has less cells in it there by increasing gaseflow but still giving filtration to harmfull elements hence still being MoT friendly or the other option a total DeCat. This is what it says it is, a DeCat - this is normally a straight pipe the same length as the cat and just replaces it altogther increasing gasflow considerably, but with out the Cat your car will Now be unable to pass an emissions test at a MoT station. Most people fit a decat and replace it with a cat before a MoT. There are manifolds with Sports Cats in them for certain VTR's but these are very expensive with most people choicing to avoid these simply because of high costs.
Sports Cats are very expensive at between £200-£300+ and although they offer a gain over a normal Cat they can not be compaired to a Decat, as the gains from a simple bit of pipe totally over out weigh the gains of the Sports Cat in terms of value for money but by doing this your car is not MoT passable. This choice is yours to make!
Sports Cat, you will be hard pressed to tell the difference between a regular Cat and a Sports Cat from the outside.
Sports exhaust with DeCat pipe, some systems come with a Decat or you can buy them on their own.
Manifold
As well as the Cat this is the most restrictive part of a cars exhaust system, some more than others its worth pointing out! By changing the way the gases exit the head and entre the exhaust its possible to change the way the car performs. Most cars have a two peice cast item from new which is heavy and restrive, by changing it to a Mild Steel or Stainless Steel item you can improve a cars performance. These are call 4 Branch as they have 1 pipe per cyclinder so on a inline 4 engine you have 4 branchs or pipes.
There are two tpes available a 4-2-1 which is 4 pipes that go into 2 pipes that go into 1 pipe which then connects to the exhaust system or Cat, there is also a 4-1 whcih is again 4 pipes but this time all 4 pipes go into 1 pipe which connects to the exhaust system or Cat. The two have a different effect on the way it improves the performance of the car whcih I will explain later. There are manifolds with Sports Cats in them for certain VTR's but these are very expensive with most people choicing to avoid these simply because of high costs.
This picture just happens to be a Mild Steel 4-2-1 manifold
Right, they are the different sections of a cars exhaust and a quick description of what they are and how they can improve a cars performance.
Because we are talking about exhaust systems and how they imrpove a cars performance, I have to mention Back Pressure. Now this is alittle complicated so bear with me.
Back Pressure
Back pressure is created in a exhaust system and the amounts of pressure effect performance. Bigger is not always better, too larger bore in a exhaust system and the gases in the system will lose pressure and the performance of your car will suffer, the same goes for if the bore is too small the gases will be restricted and again performance will suffer. Most aftermarket 'off the shelf' exhausts are the same size bore as the factory item so when buying a sports exhaust of anykind you shouldnt have to worry, but with Custom Exhausts becoming more and more common its improtant to get it right.
Custom Exhausts
With Custom exhaust, people sometimes make the mistake of fitting all straight pipework all the way back from either a Cat or Manifold straight to a Large Straight through design unoversal can, this has a effect of lowering the amounts of Back pressure in a ehaust system as the gases exit far too quickly and hence performance sufferes. Dual Exit systems also have this problem where there is more pipework than gases to fill it. Custom exhausts ie large open cans and alot of straight through large bore pipework should always be seen as a Styling mod rather than a outright performance mod. Another common mistake made by custom exhaust fabricators is they use very tight or sharp angles which having a effect on gasflow.
Custom Back boxes should be taken with a pinch of salt and the system should be well built otherwise performance could be lost.
System Layout
Back Pressue is also effected by the amount of boxes you have in a system, a Twin box system (Centre Box + Back Box) in theroy should make more back pressure than a Single box system (Just Back Box).
The theroy goes a Twin box system will improve low to mid range torque where as a Single box system will lower torque but give more mid to top end grunt. The same theroy goes for 4branch manifolds, a 4-2-1 should give more low to mid range gains where as a 4-1 should give more mid to high range gains.
Exhaust systems:
Twin Box - Low to Mid range gains
Single Box - Mid to High range gains
Manifolds:
4-2-1 - Low to Mid range gains
4-1 - Mid to High range gains
Different peole will tell you need one type or the other but I recommend either as most people remove their centre boxes for noise increases or ground cleance issues rather than performance gains.
Like I said there is No Single Best exhaust on the market today and all exhaust choices should be made by the owner of the car as it is alot of money to recommend a particular exhaust and then the owner doesnt like it.
I strongly agree with the point that a exhaust is as much a Styling mod as a Performance Mod.
Here is a short list of brand to look out for:
Ashley/Devil/Janspeed/OMP/Magnex/Mongoose/Piper/Remus/Scorpion/SuperSprint
The Big EXHAUST Thread - Please read for advice on Exhausts
...Gunmetal S Progress Thread... 
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