exhaust system mods, straight through?
 

Can I call on the collective wisdom for help. What difference does it make to throw away the makers exhaust system and fit a larger bore burgess type straight thru silencer. the initial pipe dia out of the turbo is 2,3/4in then it finally comes down to 1,3/4 at the tail pipe.
This would be into to my 97 , mazda RF turbo diesel intercooled vitara?
Theres no point in doing this if the difference is likely to be minmal.

not much point in it. diesels will send exhaust whistling before they never lose to it. most if not all exhaust mods benefit gasoline.

The only diesels I have seen benefit from opening are tractor trailers.. (4 foot long catalyst insanity).. if that is a problem on your little car, find a bigger honeycomb, and keep oem the rest.

My experience has been that the OEm exhaust system tends to be overly restrictive. It takes a ceratin amount of power to push the exhaust through the system opening things up a bit can help, assuming you don't mash the pedal too much.

Assuming you have a bit of creativity you might try a bit of creating an active exhaust system which would open things up a bit whenever the accelerator is pressed. It's an idea I initially learned about watching Top Gear, go figure. But it would give you the OEM quietness, but then by using a butterfly valve you would allow the excess pressure to escape a secondary exhaust system.

If you don't mind pissing off the neighbours you may want to remove the offending part to see if there is much difference. I suspect it would allow your turbo a bit of a quicker spool up which would obviously be helpful. if it were me, considering how it becomes more restrictive downstream I'd lop it off in a heartbeat. Invest in a high quality silencer with a larger diameter and you should be good to go.

And glad to hear from someone from the big island. Hope you enjoy yourself here.

I don't know about your particular Mazda diesel but I cut off the muffler on my VW diesel and replaced it with a straight pipe, with no real increase in noise. The cat-converter and the turbo quiets the exhaust noise nicely. It may make the turbo more efficient but I didn't see any significant gains in mpg or power. I think the upgraded exhaust may be more of an issue if you are boosting the power on your diesel than it is for high mpg at light engine loads. I deleted the muffler primarily to make more room for a belly pan install.

If you are not going to go for just for performance I would only open the system at the point it gets smaller than 2,3/4in.

A tuned exhaust will help any ICE. I drove diesel VW Rabbits for years, and was likely the first to install a Techtonics Tuning exhaust system on it. It definitely helped in the performance arena, and it was no louder than stock.
Turbo engines can often get by without a muffler, as the turbo tends to muffle the exhaust note. This is a good comparison, but not all flavors are included. V6Z24 | How-To - Choosing a muffler I had personally wished they had tried Flowmaster's racing delta 40s, but oh well.

There's a company here in the States that will install a remote turbo where the muffler used to go, says the turbo does a fine job of muffling the noise. I'd say a muffler on a turbocharged engine is just there because they're in the habit of installing mufflers on cars. Just 'cause they always used to do it, they're always going to do it.

The whole idea is to get exhaust gas out of the cylinder efficiently and getting the acceptable range of performance. Gases cool as they leave the engine and converter so a progressively smaller diameter pipe can be used. Minimizing the bends allows optimum flow. The deal with sound control is to prevent pressure wave resonance with the unibody.

Get rid of restrictions. Duramax saw 1-3mpg improvement and power gain with .5inch increase in diameter and straight through design. The benefit on a turbo motor, diesel or gas, is that the pressure past the turbo is lower than stock. This larger difference between the two sides of the turbine cause a greater speed of rotation, which equals more boost, more power, and greater efficiency (look up boost pressure and compression efficiency graphs). I would suggest it.

On NA engines you need back pressure and the oem exhaust aren't usually too bad for an ecomodder. Since your car is turbo, you need all the breathing you can get. On my performance oriented turbo Acura Integra, i ran 3" exhaust straight back and saw a huge improvement when I got it retuned.