Sports exhaust systems

If the silencers and cat-converter are swapped out for a smaller more free flowing set up with a slightly larger diameter pipe will this effect the MOT?

Will there be any difference to the fuel economy?

Will there be any difference to BHP?

Jas

Will you get away with ripping out the existing exhaust and installing a 30 inch Cherry Bomb with stainless steel 3" bore tubing to the rear? If nothing else if would sound sweet!

If you remove the original CAT and replace it with anything different, it will fail the next MOT

It can also affect many other things such as power and torque and this varies from engine to engine and vehicle to vehicle.

Generally a quality stainless steel system is a wise investment for a vehicle which is to remain with you for a long time and for various other vehicles such as 4X4's used off road and many commercial vehicles because they are obtainable cheaply and outlast steel exhausts many times, this saves considerable sums in itself and when commercials factor in lost revenue from downtime it looks even more attractive.

Stainless large bore systems do have disadvantages, generally; a larger bore exhaust may increase power slightly but this would be at the top of the rev range and you may lose some at the bottom of the rev range as these are as their name suggests, performance exhausts, this may be fine for a hard driven sports car, but for most vehicles this is a negative as they rarely use the maximum engine revs. Torque is another factor, if you gain more power you usually lose some torque and this is at the lower end of the rev range, again a heavy 4X4 relies on this torque and at the bottom end of the rev range and mid range so its not beneficial, infact its a distinct disadvantage for off road use.

In reality though, most claims for improved performance are flawed as they rely on a number of other modifications to work effectively to get the best out of the exhaust system, and in considerable testing over many years I haven't found one system which can match its claims on a rolling road, and your performance will be increased more from a drop in temperature such as winter to summer. This is because cold air is more dense than hot air entering an engine, hence intercoolers on turbocharged engines, which allows more fuel to be injected into the engine resulting in more power.

Have to agree with Assassin - the manufacturers spend £millions "getting it right" and most of the time we just mess things up by fiddling with them. Think it must be a bloke thing

Would ANY alteration to the exhaust system other than direct part replacement effect insurance? Would I need to notify them?

Jas

Its a strange one as there are a number of variables.

If you replace the system with a straight replacement or an alternative in stainless steel theres no issue as its a replacement.

If you fit a replacement which is a sports replacement then there could be issues, particularly if the cat is removed, altered, or different from the original specification as any component has to conform to "type approval" and any alterations mean it won't, and it will fail the MOT.

If you make any modification to your vehicle it will alter its value, so always notify your insurers. One friend of mine fitted a sports stainless system and they argued the value of this when the vehicle was damaged and written off in a no fault accident, basically he was hit and it was the other drivers fault, and a stainless steel exhaust was deemed to increase the value of the vehicle. They only paid him out for the value of the vehicle with a mild steel exhaust as he hadn't informed his insurers of his modification.
When he replaced his written off vehicle he replaced his exhaust with a stainless system and notified them, if the same thing happens it will be covered for the full value, premium rise? nil.