exhaust system mods, straight through?

[autoteach]

Well, there is definitely a problem with people thinking that making it bigger will make it better. A lot has to go into the calcs, including the VE of the engine, the rpms where you want the power, camshafts, intake length, etc etc. All this goes into designing a good performance exhaust. Some aftermarket companies just make everything bigger, which if coupled with 0 changes to the engine usually net a decrease in total power. Turbo engines do operate under different principles. The critical portions are the header/manifold up to the turbo, which people typically leave alone, and the pressure difference between either side of the exhaust turbine, which dictates lift on the blades, which effects rpm-boost-power, and so on. There are points of diminishing returns, where the bigger pipes net no increase in power.

[copternadley]

Originally Posted by ted frater

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.

You can do a thorough research on that one to further lighten your decision on what to do with it. Also suggestions here can also help you decide.

[TOOQIKK]

Originally Posted by COcyclist

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 it makes the turbo more efficient then you dont have to step on the gas pedal as hard or as long to get to speed that will increase your mpg.
exhaust mods help your top end power and efficiency
intake mods help your lower end power and efficiency

i would recommend a 3" exhaust for a turboed vehicle.

[COcyclist]

Originally Posted by autoteach

Turbo engines do operate under different principles. The critical portions are the header/manifold up to the turbo, which people typically leave alone, and the pressure difference between either side of the exhaust turbine, which dictates lift on the blades, which effects rpm-boost-power, and so on. There are points of diminishing returns, where the bigger pipes net no increase in power.

So Autoteach, I read the Exhaust Theory 101 and I get the exhaust scavenging concept. But in a turbo car, does this mean that the whirring turbine blades eliminate the pulses at the turbo and therefore from that point on bigger is better, even for ecodriving? A 3" exhaust on a 1.9 TDI could increase mpg at light engine loads?

[aerohead]

Originally Posted by ted frater

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.

So far,to my knowledge,no one has done a scientific investigation on exhaust systems modification.
If you would like to be the first it would be great.
You would first need to drill and install pressure taps along the entire length of the exhaust system,at every transition,in every component,stem to stern.
Secondly,you would need to operate your car on a chassis dynamometer under all transient load and steady load conditions,constructing a complete manometer histogram of the exhaust system,normalized to standard temperature and barometric pressure,while simultaneously recording horsepower.
After which,you would repeat the process with the modified exhaust system,and after data reduction,compare the two sets of data to ascertain at which point the modification yielded a beneficial performance enhancement.
Short of all this,it would be very difficult to know any specifics.

[autoteach]

Originally Posted by COcyclist

So Autoteach, I read the Exhaust Theory 101 and I get the exhaust scavenging concept. But in a turbo car, does this mean that the whirring turbine blades eliminate the pulses at the turbo and therefore from that point on bigger is better, even for ecodriving? A 3" exhaust on a 1.9 TDI could increase mpg at light engine loads?

Sorry it took so long for me to reply...
Pressure waves, for the most part, would be reflected at the turbo and back towards the cylinders. The critical aspect that is occurring before and after the turbo (remember that each vane is a wing, and lift has to do with the pressure difference above and below, along with SA), so less restriction after the turbo will definitely increase turbo pressure and spooling at all rpms. To understand why this is good for all driving, including ecodriving, you need to look at engine efficiency:


http://www.rm-indy.com/compression_vs_boost.htm

By increasing boost, you increase thermal efficiency, or power output, which requires less throttle, and less fuel (see thermal efficiency). Turbo vehicles see gains after the turbo in both low/top end power and mpg.

[COcyclist]

In that case I would recommend TDI owners ditch the 14 lb. muffler for a straight pipe. When my factory exhaust rusts out I'll go oversize from the turbo back. This sounds like one of those rare cases where you get both more power and better economy at the same time.

[JRobbins]

I'm not sure if it has been mentioned, but turbos do like to have back-pressure from the exhaust.

[COcyclist]

Originally Posted by JRobbins

I'm not sure if it has been mentioned, but turbos do like to have back-pressure from the exhaust.

Please include links to documents or tests supporting your claim.

[micondie]

try this site for basics:Turbo Vs. Supercharger Power Consumption | eHow.com