Nissan Patrol 4x4 (Africa)

Yip on a turbo car the turbo acts like a silencer and makes the exhaust note quieter.

On the petrol Patrols the large suitcase like silencer in the middle plays the biggest role in silencing (and restriction second to the cat) as the other 2 smaller ones are free-flow boxes. The small one at the back stops the exhaust 'drone' on the open road.

I would only remove the cat as replacing the big box with a free-flow one only marginally improved performance and had no effect on economy.
I think by removing the cat should have a minimal effect on the exhaust noise as the older cars like mine never had a cat.

Interesting - mine is a 2005... so maybe does not have a CAT anyway.
Will check tonight!

Yes - it is weird because I think Alex said he had a cat on a 2004 model and I definitely don't have one on my 2006 4.8

It might also depends on what spec it was build to - Middle East / Europe etc.
Looks like there is either a cat or a small silencer but not both.

ricster wrote:I may be wrong here, so please correct me if I am...... but petrols and diesels work very different from each other. A diesel you can remove all the silencers and just have one lekker big pipe as an exhaust. But on a petrol motor you need a certain amount of back pressure, which is achieved by means of the various silencers. My question is.... Is just the little rear silencer able to give enough back pressure? Changing the exhaust pipe diameter, will also have some kind of effect on how the air flows in the pipe. Possibly a small silencer needs to be fitted to assist with this.

Well I might be wrong here and not you, but I don't agree that an engine needs back pressure...... Both diesel and petrol engines will run better with less back pressure if the air and fuel ratio is maintained at 14.7:1
Some people claim that you get better low end torque if you have increase the back pressure, but this may be a result of a richer running engine because of less oxygen being sucked into the combustion chamber.
There are also the other theory of burnt valves because of less back pressure. This also is the result of more air being sucked into the combustion chamber because of a more free flowing exhaust and this results in a leaner air/fuel mixture which makes the valves burn. So its not the exhaust that burns your valves but the lean air/fuel ratio.

The idea that a petrol engine needs back-pressure is pure myth, as Michael says. Aircraft engines seldom if ever have these silencer things.

Removing a cat should make very little difference, unless it was seriously clogged, in which case it might make some difference.

Yes the best silencer is no silencer but that gets a bit loud for most of us.

As mentioned above - from the schematic it looks like you have either a cat or a small silencer. If there is a cat I would first replace it with a straight pipe and then if it is too loud I will put in a small free flow silencer.

Has anyone had an experiences where the main silencer became blocked due to internals shifting ?

AndriesS wrote:Has anyone had an experiences where the main silencer became blocked due to internals shifting ?

Jip I had it car became sluggish and intermittently lost power and felt pap when I removed the coffin box and replaced with big free flow box it was as if someone pressed the turbo button
I think what happens with a lot of patrols that doesn't run every day the exhaust gets more water in and rust create a lot of problems. ....

Thanks Tinus, I also have a new rattle (one you can only hear when the window is open ) but have not been able to identify it - I think it might be the silencer.

We really need to get some sound clips of various free flows. The standard Patrol is so quiet you can creep up on pedestrian and give them a good fright.

My big suitcase silencer also had loose baffles which rattled and irritated the blue $%#@ out of me . Replaced with big Powerflow S/Steel box.