Rover 200 & 400 Owners Club

this is pure curiosity.... does a bigger or smaller mid silencer produce a louder or not so load back box noise?

smaller = more noise, more power hence more chick apeal - i keep tellin em samller is better..

The middle box is usually a resonator box. This gets rid of the raspy sound of the exhaust to an extent, many turbo cars can do without this as the turbo itself is good at getting rid of the raspy noise.

The backbox tends to smooth the pulses further.

The bigger the middle box in general the less raspy the exhaust note.

Note that smaller does NOT mean more power. It can sometimes mean this but it can sometimes mean the opposite. There is a lot of science on pulsewave tuning etc if you really get into proper performance exhaust design.

Note that smaller does NOT mean more power.

why do you think that less resistance/turbulance wouldn't promt more pony?? yes it could make it a little less green, but more power me thinks from smaller or better still no silencer. try removing the exhaust entirely - mine deffo grabs over half a second to 60 (may not be alot but every little helps)

Trouble wrote:

Note that smaller does NOT mean more power.

why do you think that less resistance/turbulance wouldn't promt more pony?? yes it could make it a little less green, but more power me thinks from smaller or better still no silencer. try removing the exhaust entirely - mine deffo grabs over half a second to 60 (may not be alot but every little helps)

Because of a very useful phenomena called pulse wave tuning. Essentially you use the energy of the exhaust gases to help suck the exhaust gases out of the next cylinder to empty. If it was as simple as removing the exhaust to increase power then why do F1 teams spend hundreds of thousands on exhaust design every year as they don't have to meet any noise regs.

Most people confuse louder with faster, hence all the chav cars with big bore exhausts and open cone filters. It is a proven fact that many engines loose power and torque when you run big bore exhausts on them. If you have a read of some of the better tuning books out there you should find some far better explanations than mine. Anything by Vizard for example is usually pretty good.

I really don't feel I should reply to your question! Manufacturers go the extra mile to make exhaust emmisions & exhaust baffling as the optimum for the engine. Why make more noise to gain whatever..unless you're a boy racer! All you do is waste your money & make an annoying noise! Dave

In general maufacturers will seek to reduce noise inside the passenger cabin so power gains may be possible, however more noise does not equal more power always. In some cases it does, however not in all cases it is far more complicated than that.

For example I designed an exhaust which gave an improvement of 6bhp (dyno proven on the same car on the same day). That doesn't sound a lot but it was about 5% increase which is about as much as you can expect with this engine.

that pulse wave tuning stuff doesn't and couldn't use middle box silencers - it involves just balancing the cylinders out and as you said drawing out the next sequenced cylinder by mating it at the appropriate place to suck in the power band - back pressure is bad in any form apart from making the car more green and possibly more fuel efficient.

dave, i agree exhausts are made enhance a cars efficiency and energy despersal, but thats not the point of the question - a smaller midbox is louder and produces more power.

so sticking firm here and looking for someone else to back me up ignoring possible engine management sensors mess up - a smaller or no middle box promts more pony!!


clawjaw mate, back my corner here! u started it!!

Sorry but you wrong. Do you know the difference between a resonator and a muffler silencer? They work in different ways.

Pulse wave tuning is primarily involved with inlet and exhaust manifolds, however it does have a significant effect on an engines breathing.

This is why 4 into 2 into 1 exhausts are popular performance upgrades as they offer inproved scavenging and so usually improve midrange torque. It depends on design of course but in general that is what usually happens.

Backpressure is not all bad it helps keep the intake charge where it should be (in the cylinders rather than the exhaust), so improving economy, reducing emissions and improving power as the fuel is where it should be!

If getting rid of the entire exhaust after the downpipe produced more power why do you think proper race cars, rally cars, touring cars, and all sports cars don't run like this? It'd save them weight and expense. Because it doesn't work is the answer.

Produce some evidence that your theory is sound and I might change my mind. Until then I'll believe the rather more respected tuning gurus such as Mr Vizard et al.