MGZR Ezhaust.

[Ozzyman]

I've recently had a "Powerflow" stainless steel back box fitted to my MGZR 105+ mainly for a better sound and with the possibility of gradually renewing the whole system as and when it needs it. The disappointment I have is when revs are between 4- 6,000 it not only seems a bit on the noisy side but the acceleration isn't as brisk as with the standard silencer on.! Or am I imagining it ? Has any body suffered with this or could give me some advice. The end pipe is oval by the way.

[kramer81]

Ive heard performance mods such as exhausts can slightly boost horsepower at the expense of some torque. Wouldn't have thought just a back box would make much difference though

[Impret-Sir]

A well designed replacement back box can liberate only a small amount of extra BHP, usually about 3 to 5 BHP over the standard system. On its own it cant do more, as the restrictions of the manifold and the rest of the system are still present. It could be that your original exhaust was well enough designed that it made the most of your engines power output allready, so very little if any improvement was possible. Im not surprised it sounds noisier, that is usually the whole point of fitting a back box, to make the car seem faster even if it isnt! The replacemnt one will be made from a larger bore pipe and have less baffles in it than the original, so it will muffle the sound less, hence it will be noisier. To notice any real performance gains you will need to change the whole system, and the manifold, ideally added to an improvement in the airflow into the engine as well, with a performance air filter. These modes may make your car run a little lean, so a proper setting up might be required to get the best effect and reliability. Its a fact that manufactures seldom publish that you cant just stick on a noisy back box and get a big power hike. Incedentally, you catalytic converter will also sap a bit of power, a lot of the Impreza guys I know who run their cars with big exhausts for maximum power remove the cats to do so, then replace them for MOT time.

[madein1978]

You will only get a power increase if you put on a complete big bore system on, that is manifold to backbox, bolting on just a backbox will only cause it to make a racket and possibly drop in power. You can actually get a high flow sports catalyst as well which will liberate more power, don't however be tempted to lose the cat altogether as it is illegal (Construction & Use act) to run a post 1992 car without one and it will fail the MOT. The full system will make it sound truly sporty and not like a bee that has a dose of the sh*ts! You could also put a K&N High Flow air filter on too, this will give you another 3-5 brake to play with. Good luck, the quest for more speed is fun!

[madein1978]

I know of guys that have removed their cats who have been pulled by the Gestapo because they could smell the exhaust fumes of a non cat car which was of legal cat age.

[kramer81]

I think he is saying his performance has suffered rather than not improved