Benefits of a Stainless Steel 'Sports' Exhaust
All car manufacturers are compelled to comply with ever more stringent worldwide emission and sound regulations and now seem to apply the strictest of these to all their models.
* We can improve on the materials used to provide longer component life.
* Superior quality materials allow reduced weight to benefit all areas of performance.
For example our Lamborghini Murcielago system eliminates over 30 kilos and our Lotus Exige ‘Ti’ system saves 8.2 kilos – both from the rear of the car & improving balance.
If appropriate we can design the exhaust to allow a worthwhile reduction in the centre of gravity as with our Ferrari 360 and Porsche GT3 SuperSports systems.
* We allow personalisation by providing an alternative appearance with different tail-pipe designs and polished silencers.
* We can improve on the performance (especially on forced induction models) by reducing the internal restriction.
* Sound is one of the most important sensations of enjoying a Sports Car. We provide the freedom to choose a level of sound that is appropriate to you.
Our ‘straight through’ silencers contain a perforated tube surrounded by a finely-woven metal sock. Made from semi-continuous (Type 434) stainless steel filaments this sock outperforms conventional glass and basalt alternatives at high temperature and is used to insulate and retain the acoustic stuffing. This is an essential component for most high temperature applications.
For sound absorption we still employ long strand Basalt filament that offers excellent acoustic performance up to 1500 Hz. It's thermal properties are comparable with continuous high temperature glass but more stable at temperatures over 600° C. This material requires rigid handling procedures in the factory.
So, for environmental reasons we are moving over to use Advantex and Acousta-Fil stuffing, these have similar temperature and acoustic properties as the Basalt .
Advantex is manufactured by Owens Corning Corp. Says Heinz Otto, President, Composites Systems Business. "The glass fiber remains in place, even under the harshest conditions, meeting manufacturer’s extended warranty requirements. This has been proven at Toyota, Volvo, DaimlerChrysler and GM Opel”.
In our conventional chambered silencers we employ various techniques to fabricate all the internal components. Stricter emissions regulations are demanding ever-more complex silencer designs and here are a couple of cutaway drawings made for us by the late Bob Freeman. The first is a Ferrari F355 silencer showing seven internal chambers in one silencer and featuring internal tubes of different length & diameter to produce musical chords at different pressures. The second is another Ferrari, a 550, with a similar layout.
'Sports' Exhaust Development
After identifying a car that we should be manufacturing a QuickSilver exhaust for, we review the car’s performance, see how the manufacturer has designed the original exhaust and then decide how, and if, we can improve it.
What combination of improvements or advantages can we provide?
And what will the customers for this model demand?
After answering these questions we manufacture a prototype and obtain a car for testing.
We often develop new systems in partnership with a specialist in that make, where we can combine his experience of the model with our exhaust skills.
The next stage is to quantify the improvements by measuring the sound volumes, weights and performance gains.
Is the fitting process manageable? Are the expected benefits present? Is the cost sensible? Is the appearance correct? Is the sound quality right?
Sometimes this process must be repeated but eventually, when the answer to these is positive, the newest QuickSilver ‘Sports’ exhaust can proceed to production.
We employ various techniques for tube manipulation, most commonly:
Our volume systems are mandrel bent on our Addison DB76 Databend machines. This CNC machine pulls the tube around formers whilst a ‘snake’ of articulated balls (the Mandrels) are simultaneously pulled through the tube to maintain it’s section and produce the highest quality bends.
Our single or low-volume ‘classic’ systems are usually press bent on Ben Pearson Tubemaster machinery. The tube is first cut to the appropriate length, one end has a plug welded, it is completely filled with dry silver sand, the other end is welded up and then this solid tube is bent cold. The sand fill ensures that the tube maintains it’s section during bending in this simple but laborious process.
Stainless Steel - There are around 120 different alloys of stainless steel, with various properties, those mainly used for car exhausts are:
Type 304 austenitic is generally regarded as the best grade for automotive use and this is the alloy that we use, in plain and annealed form, for 98% of our exhaust systems because of it’s combination of availability, formability, durability and cost. Chromium (10%) and Nickel (19%) are added to the base steel. As a non-magnetic material it is particularly specified for armoured vehicles. It has excellent corrosion resistance.
Type 409 is probably the most popular grade for original equipment exhaust components and especially catalytic converter casings and pipes. Chromium (11%) is the main addition to the base steel. Ultimate corrosion resistance is not as good as type 304 but the cost is lower and availability excellent.
Types 316 and 321 are similar to 304 and occasionally used for automotive exhausts. They have particular chemical and heat resistance virtues.
Types 309 and 441 are two examples of specialist alloys with particularly high resistance to heat and stress. We were recently asked by a major Sports Car manufacturer to employ these grades in an exhaust manifold for a special model that was subject to extraordinary conditions – ‘US market Federal Certification requires original-equipment emission-critical components to have a life of 10 years’.
Titanium - and its alloys are relatively new engineering metals since they have been in use only since about 1952. Titanium is not an 'exotic' metal, it is the fourth most abundant structural metal in the earth's crust. It is an extremely attractive material for engineers because of it’s high strength to weight ratio, high elevated temperature properties and excellent corrosion resistance.
We presently use Titanium in some of our Lotus exhausts and, as the availability of appropriate tube and sheet improves, we are looking forward to finding more applications for this material.
Stainless Steel and the Environment
The main source of Raw Material for making stainless steel is re-cycled metal.
This re-cycling route has been established for many years and the economics of the stainless steel-making industry depend on re-cycling.
Worldwide, over 90% of new stainless steel is produced from re-cycled material.
The steel is melted electrically and in most cases refined by using inert air-distilled gases, such as argon. Great care is taken to minimise fume and dust emissions, some plants are equipped to re-cycle dust into the steel making process.
Most of the materials consumed during the steel-making process, including cooling water, lubricating oils, pickling acids and "inter-leaving" paper are re-cycled in the plant or by specialist contractors.
It is economically advantageous for stainless steel fabricators and processors to ensure their scrap and in-process consumables are returned for re-cycling. Our waste materials are collected weekly.
As stainless steels are corrosion resistant their life expectancy is unusually long. A minimum of maintenance is needed and so, although more expensive initially, they offer attractive "life-cycle cost" benefits over alternatives such as mild steels.
There are no proven health risks from the normal use of stainless steels
'Sports' Catalytic Converters
Most car exhausts have been fitted with a catalytic converter containing a Ceramic core or ‘brick’ (which it resembles).
These ceramic catalysts have cores with the equivalent of about 800 cells per square inch (cpsi) giving a flow area of approx 45%.
The ceramic cores work over a relatively short temperature range, can be subject to overheating damage and are vulnerable to impact damage due to their lack of flexibility.
The modern Metallic ‘Sports’ Cat has a microscopically thin Fecralloy honeycomb metallic core of (usually about) 200 cpsi to which the essential Platinum and Rhodium are applied at a much greater density (25 grams per cubic foot compared to 10 grams on a typical ceramic product). This all results in a flow area of approx 85% whilst remaining clean enough to meet emissions requirements.
Their greater efficiency allows these metallic cats to be smaller, lighter and their durability is superior. Most modern ‘Prestige’ cars now have metallic cats as original equipment.
Superior Materials, more efficient flow, less weight, smaller size, better sound, longer life - through the use of Titanium and Composite materials as well as different stainless alloys & innovative internal designs > to produce the result the customer wants.
Of particular interest at present is the development of a sintered stainless tubing. This is composed of compressed stainless fibres of variable densities which have the potential to offer acoustic properties within the tubing of an exhaust system - offering the reduction and perhaps even the elimination of the silencers.