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Frequently Asked Questions - Exhaust Systems
 
Exhaust manifold types
Exhaust system affecting performance
Exhaust system noise levels
Exhaust box decibel level
Rasping noise in the exhaust tone at 3000rpm
 
Exhaust manifold types
Question: I would like to know the difference between type A exhaust manifold and type C exhaust manifold. Also is Type c exhaust manifold for c20xe the same as x16xe. I understand that you can buy specification from you and fabricate at manufacturer of your choice, I would like to know how much is the for the design specification and how to order.

Answer: Due to the high level of performance and the large range of vehicles that our engines are fitted to, we have now stopped producing a range of exhaust manifolds. When we originally started, there were exhaust manifold that could simply be purchased from various manufacturers that would simply fit a model of car, these were quite often manufactured at a price to be affordable. But over time, as we developed our engines, the exhaust manifolds became more advanced to produce optimum performance. Each time a new design was produced, it was given a new letter but because it became impossible to manufacture and hold quantities of exhaust manifolds and the designs became ever more complex and kit specific on many occasions, this has now stopped. There are still many road based affordable exhaust manifolds manufactured by various companies and many of these are well made, but not suitable for high end performance.

The dimensions for the 1.6L engine and the 2.0L engine are different due to its capacity, effectively any exhaust manifold design that we would sell are for maximum overall performance. The cost of the design is £75.00 + VAT, I have attached a link below which shows the kind of information you receive, which you would then present to your exhaust manufacturer. When requesting an exhaust manifold design, please give as much detail as possible about your engine e.g. cam profiles, compression ratio, cylinder head port work spec, valve size, throttle body design, etc. 

Links: Exhaust Systems

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Exhaust system affecting performance
Question: I decided to have an exhaust manifold and system made, unfortunately your recommended manufacturer was too expensive, so I choose another supplier whose price was more affordable. When the car was finished, the exhaust system looked fantastic and the welding was excellent, unfortunately when it was put on the rolling road the performance did not match what I was expecting. The guys running the rolling road said the engine was performing unusually and believed it was something to do with the exhaust manifold. What can I do?

Answer: I would check your exhaust manifold dimensions very carefully to ensure all the pipes are equal and the correct length, if they are not, which is quite likely then the contact the manufacturer and see what they are prepared to do for you. Hopefully they will sort the issues out for you, unfortunately the difference between a cheap exhaust manifold and a manifold made to the correct dimensions can take 4 or 5 times longer to manufacture and it is only when you come to measure the manifold itself after an issue has arisen, that this problem is discovered. We have investigated in the past, cheaper alternatives but have always been let down and as the old saying goes you only get what you pay for.

Links: Exhaust Systems

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Exhaust system noise levels
Question: I purchased a 4-2-1 manifold and titanium silencer for my Westfield a couple of weeks ago, I very impressed with the build quality and power gains. I went to a track day on Friday and the exhaust measured 99.2db. The main reason for me going with the SBD system was I was under the impression it was track day friendly but with most noise limits at 100db I'll be right on the limit. Have your manifolds been tested for noise levels?

Answer: Glad to hear the exhaust system and manifold have made a significant improvement to the performance of your engine. As far as decibel levels are concerned, it is impossible to give a decibel level that you are likely to see. We have done extensive testing over several years. We have even got to the point where we have tested two identical cars, with identical exhaust systems and boxes and have both read 5 db different. We have then swapped the exhaust box over and found the decibel level has still remained the same (i.e. car A produced 100db, car B produced 105db with exhaust boxes swapped, car A still produced 100db and car B still produced 105db). More often than not the decibel level recorded is produced by the intake system. Also the body panels and components on the car vibrate. We have supplied air intake systems to some customers and they have found a dramatic decibel drop, even though the decibel level is checked by the exhaust pipe.

There are numerous other reasons the decibel level can vary, even down to atmospheric levels where the car has been measured on concrete, grass, near other cars etc. The more highly tuned the engine the louder the engine gets as well. We also find that when the exhaust boxes are new, they are usually slightly louder than after they have been run for a while when the packaging has had time to settle down.

We normally reckon that it is possible with a standard engine on throttle bodies (carbs are usually slightly louder), to achieve almost under every condition under 105db. We have in the past seen as low as 94db, but this was when the engines used to be revved to 3-4,000 rpm. Unfortunately the track days are now asking for decibel levels of such ridiculously low levels, that it will be soon impossible to get through noise without physically restricting your exhaust system and losing power. To give you an idea, a few years ago when I took my ARDS test, I was driving a Volvo V70. I was told by the instructor that on certain days, it failed to get below 100db. This car was completely standard.

Links: Exhaust Systems

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Exhaust box decibel level
Question: Please can you tell me what the decibel level your exhaust boxes have?

Answer: The decibel level (db) of the exhaust box will depend on the specification of your engine and atmospheric conditions. For example a 2.0L XE engine will produce approx. 97db at 4,500rpm at half a metre. Whereas the same exhaust fitted to an engine producing 250bhp could produce 102db at the same revs. These reading could vary by as much as + or – 3db with a change of weather conditions. We are continually trying to improve our exhaust boxes to accommodate the ever-tighter noise restrictions being applied on motor sport and track days without loosing your expensive engines performance, but with the levels now being applied in some case it will be necessary fit baffles fitted to achieve the required limits but this will mean loosing BHP.

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Rasping noise in the exhaust tone at 3000rpm
Question: The exhaust tone on my Astra 2.0L 16v GSI is making a horrible rasping noise when I am at about 3000 rpm, it sounds like metal touching metal and vibrating (I have checked and found nothing). Would one of your manifolds remove this problem?

Answer: It is obviously very difficult to diagnose a noise without actually seeing the car. Certainly the 4 wheel drive and 2 wheel drive Cavaliers produce a noise such as you describe (whether it is the same noise without seeing the car, I would not like to guess further). The noise we know of is caused by the induction and the exhaust pulses producing the rasp noise you described at a specific rpm. There is nothing normally wrong with the noise and it does not affect the performance of the engine as such. Changing the exhaust manifold or indeed exhaust system, or both can sometimes alter the point at which this noise occurs and sometimes even reduce it. But I would not like to guarantee that. Our exhaust manifold would certainly improve the performance of your car. We have had reports from one of our customers who already has a free flow exhaust fitted to their XE engine in a FWD car and then fitted one of our exhaust manifolds and commented that he saw a 12bhp increase (we would normally only say a 6 - 8 bhp increase).

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