2005 Mazda Bravo Exhaust upgrade 2.5, 2.75 or 3

oops forgot to add, im going to get a full system from the turbo back :D

G'day Max
Here in Texas everything is better if it is bigger. Unfortunately Orstrayans believe that too.
Thinking Australians do some checking like you are doing.
A 4.5 litre turbo Landcruiser is sometimes upgraded to a 3" system to help clear gasses.
I think they have the ability to create far more exhaust gas than yours ever will.

Often 3 Litre diesels are also 3"ed too, some good some not as good all round.

The engine pipe on a stock PJ BT50 is 63mm OD. but the same section of pipe on the same year Dmax is barely50mm 2", but increases towards the rear and through the muffler to 63 or 2 1/2" Both work ok.

As exhaust gas goes into the exhaust engine pipe usually bigger it is cooling, the more it travels in the pipe the more it expands and therefore cools more, therefore the rear pipe doesn't have to be as big as the front sections because the size of the gas is much smaller. Because of the surface area of a muffler the gas expands and cools and the muffler also cools it dramatically and then there is far less volume to the rear pipe to worry about.

Yours might benefit from a larger dump pipe than OE and the same for a distance back and then it can be smaller.
Not knowing the current sizes it is hard to tell what may be of benefit.

The same size all the way through usually isn't needed but they are made that way for ease of production and monetary reasons. ALSO KOOL, not heat type cool though.
Often the statement is made, that the OE mufflers are restrictive, some may be and some not. No one gives any data as to the reality of that I have noticed.

Depending on the OE sizes of the pipes a little larger will be of help in clearing, Too big will be noisey and likely create heaps of turbo whistle, (KOOL when fitted PIA afterwards) or when Boy in Blue/Black listens too. That size will cost more and achieve little.

On a 3litre Dmax, I use 3" dump and front pipe (IMO too big for your engine) and then use a tapered pipe to feed into the OE muffler and rear pipe. Both 2 1/2". Clean sound, minimal whistle, noticeable increase in getup and go, similar economy but seems to cruise with very smooth running and doesn't wake neighbours or attract unwanted attention.
Your decision though.
Cheers
Ross M

Anybody got any experience with 2.5 TD engines????

surely someone has had an exhaust done

2.5" is a good size for a 4 cylinder motor it will increase your power output improve economy & still maintain reasonable back pressure to help hold the gear on downhill runs if you go to big you'll be riding the brakes all the time like a petrol motor. If it was a race car with a worked motor you might go 3". On the intercooler side of things it $2000 is a ridiculous amount for just an upgrade you can do it for a lot cheaper I would do more research so you don't get ripped off. I can set up a 31" wide front mount air to air on a GQ for around $300 - $400 give or take a bit.