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

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.

Answer: We produce two manifolds that customers have fitted to the Corsa. I wouldn't say the pipes as they come out of the cylinder head turn any tighter than standard, because they are designed to produce as much power as possible. They were originally designed for use on the Astra and even our high spec manifold, hugs the sump pan very tightly. To give you an idea of how close, you would have to remove the exhaust manifold studs from the head and slide the exhaust up vertically in order to get it to fit. The fast road spec exhaust manifold, which takes up approximately the same space as the original XE manifold, is currently available from stock. Part no. EX-M-CAV-GSI16V. The high spec exhaust manifold that requires a 2.5” exhaust system is EX-M-AST3-S16V

Links: Exhaust Manifolds

Answer: The tarmac exhaust manifold is still available and because the dimensions of the Calibra engine bay are identical to that of the Astra, it will fit in exactly the same way as the Astra engine bay. The diameters of the primary pipes are 1.7/8" and the secondaries are 2.1/8". The outlet diameter into the first part of the system is 2.5". This was then stepped up to 70mm to match onto the works exhaust systems
I would not recommend a 4 into 1 exhaust manifold. It only produces peak power and loses dramatic amounts of mid range and lower end torque and our design of exhaust manifold is superior in every way.

Links: Exhaust Manifolds

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).

Answer: The standard exhaust systems fitted to the Caterhams are fairly restrictive. Their 4:1 competition manifold is a significant improvement, in our opinion it is not as good as using one of our 4:2:1 manifolds, which will increase the top end rev range as well as increasing the mid range. Whereas a 4:1 only improves the top end & sacrifices the mid range.