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Welcome to the MGF/TF Exhaust pages!
In this section of the site, I've attempted to collate as much information regarding exhaust systems as possible - hopefully you'll find it of interest! Use the menu above to skip to other pages in this section, whilst on this page you'll find info regarding the purpose of exhausts, the potential benefits of sports exhaust systems, and HOW the exhaust system works.
Why are exhaust pipes fitted to our cars?
The purpose of the exhaust system is simple: to channel the fiercely hot products of fuel combustion away from the engine and the car's occupants and out into the atmosphere.
The exhaust system has a secondary purpose- to reduce the amount of noise made. The exhaust gases leave the engine at incredibly high speeds. Moreover, with the opening and shutting of the exhaust valves with each cycle of combustion for each cylinder, the gas pressure alternates from high to low causing a vibration- and hence sound. A very loud sound if there is no silencer there to reduce it!!!
As a population we are demanding less and less noise pollution from our cars, so the 'powers that be' have legislated 'drive-by' noise regulations. To this end a silencer has to muffle the vibrations of the exhaust gases, reduce their velocity and thus reduce the amount of noise emitted from the engines.
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How does the MG exhaust system work?
Like any other vehicle, the mid-engined MGs exhaust system comprises of four basic sections: exhaust manifold, catalyst, mid-section, and back box (also known as the 'silencer'). But because the mid-engined layout of the MGF/TF, the mid-section is somewhat truncated! Pictured opposite is a schematic of the various sections that comprise the standard exhaust system, as fitted to pre-2000 model MGFs. Everything in red is the system up to the silencer...
Exhaust gases leave the engine via the four cylinder head ports and into the exhaust manifold (also known as a 'header') [1]. These gases are collected together, down into a single pipe, known as a 'down pipe' [2] and then through a flexible section under the engine's sump (the 'flexipipe')[3]. (As you can see from the picture opposite, the distinction between down-pipe and flexipipe is purely arbitrary, and this section is often referred to by either name.) From here, the gases pass through the catalytic converter [4]- that in itself will slow and quieten the exhaust quite a lot (one reason why some choose to remove the catalytic converter!). And finally, the 'cleansed' exhaust gases exit via the silencer[5] through the twin tail pipes.
Too quiet?
Some would argue that modern cars are now too
quiet. Well, for a sports car anyway. Enthusiastic owners are often keen to hear
a little more noise from their car's engine - to add a little more 'sporty' character if
you like into what can be quite a anodyne exhaust tone. This is reason enough for many to
consider purchasing a 'sports exhaust'.
Potential power gains?
As mentioned above, the exhaust silencer is designed to muffle the exhaust gases and slow them down. In doing so, exhaust systems can cause a restriction to gas flow and effectively 'choke' the engine (increased back-pressure). There is therefore potential for a sports exhaust manufacturer to put together a freer flowing exhaust system that lets more gas out. As they need not be too concerned with the need to meet stringent original equipment manufacturer restrictions on noise, then all the better: one less compromise to worry about!
Sports exhaust systems
Are all exhaust systems the same? No they are not:
there is a surprising variety of options available offering different sounds, tail pipe
finishes, quality and cost. Choosing one can prove to be a somewhat bewildering
experience!
Sound quality: Each sports exhaust system produces quite a different noise from another- from the low, bass-like rumble associated with the Trevor Taylor Fxtreme and Phoenix, via the delightfully fruity Janspeed and Mike Satur Daytona to the higher pitched wail of the Milltek Supersports there is a system to suit everyone!
Volume: Sports exhaust systems also vary according to HOW loud they are- the Trevor Taylor system easily being the loudest, to the most refined Double S system available through the MGOC.
Material of construction: There are also differences in materials used in construction- mild steel versus stainless steel.This is usually reflected in the purchase price- a mild steel system usually being about 100 GBP less than the stainless steel equivalent. The advantage of stainless steel of course is longevity. If you intend to keep your MG for a long time, then perhaps this is the material of preference. Aftermarket systems are often sold with a lifetime guaranty (although unfortunately, these tend only apply to the original purchasor). You may be interested to know, by the way, that the pre-2000 model year standard exhaust system is made of stainless steel...
How do exhaust silencers work?
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SP Exposed!
The pictures shown here (right and below) are of a
Milltek Supersports exhaust system formerly fitted to Roger Parker's MGF. Fed up
with the increasing volume from this after market system, he cut it open to figure out
what made it 'tick'. I'm very grateful that he did!
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From the catalyst, the gases turn through a lazy 180 degree turn and enter the silencer box through pipe (A) in the right hand picture. That middle chamber should be filled with wire wadding to dampen exhaust noise- but here the wadding had all but disappeared. This is a problem with stainless systems- although outwardly they look perfectly good, their silencing performance can drop off markedly over time.
Back to the plot. From pipe A, the gases cross the central chamber and pass into the right hand chamber (as you can see from all the soot). The gasses then pass from chamber to chamber equalising the pressure pulses via the perforated tube, B. The exhaust gases eventually exit via the tail pipes, C.