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.

NA engines need back pressure?

Actually any vehicle never needs back pressure that is often a misconception made by those who go to to big of a pipe and lose performance. The reason this happens is that going to to large of a pipe exhaust gas cools and then slows. When that happens there is congestion in the pipe and then the motor has to work more to push the slower gases out.

With an appropriately sized pipe it will remove nearly all back pressure and promote the removal of gases since they will be moving faster. When the gas tries to quickly remove its self it creates a pressure wave behind it that works to suck the next exhaust pulse out of the pipe. That is what you are going for with any exhaust system.

^Very well said. The back-pressure thing has always been a misconception.

For NA engines, going to a diameter that is too large will reduce flow velocity and reduce power. Getting the highest-flowing cat and muffler you can find for your stock size is your best bet.

My Tempo has a 2 inch system, but the stock muffler had a 1 3/4" outlet. Changed it out and immediately noted an improvement in power on the high end.

For gas-miserly driving, you're not really going to go into the RPM range to take advantage of higher-flow exhausts.

You know what back pressure is? Its resistance coming out of the pipe because of smaller diameter/ resenators/ cats/ muffler. Little pipe = back pressure, large pipe = free flowing. NA engines NEED back pressure. If you removed your exhaust system after your cat, you would loose performance and MPG in your na motor. On a turbo motor, an open down pipe is the way to go.

i did notice my maxima has an insulated exhaust system. Maybe that is why, to preserve the heat all the way to the end.

There is very little science in that article and its all to do with a/f ratio which is also determined before entering the motor.

Put it like this, if you take my stock d16y8 out of my civic and put on a header into a 3" collector and then straight back, you will LOOSE power. Dyno proven. v8 motors use X pipes to increase back pressure for low end torque.

All in all, im not sure about the effects on fuel economy.

WHOA! science content is definitely in question throughout this thread. I could go on to explain, but it seems like this would give you enough of the information that you need.

Exhaust System Theory 101

If you read through it, you will see that back pressure, which will occur in low diameter tubes at higher rpm, is not what increases the torque, but the exhaust scavenging that happens due to the fact that your combusted air/fuel , in fact, has enough mass that at the velocity (e=m*v*v) it has significant momentum. This, coupled with overlap of the intake and exhaust lobes with each other, and the trail of that lift into the surrounding strokes, increases volumetric efficiency, which increases torque at that rpm. This is not the same as welding your 5" muffler shut to a 1", which would increase the back pressure, but not the velocities that the exhaust would be seeing in the more critical sections that effect this scavenging effect. You also should look up what an x pipe does (hint, increase cross scavenging between the two banks of cylinders) along with tri-y headers. A good rule would be that as temperature drops and density increases, diameter should as well. An exhaust system that has such a taper would be expensive to build, hence why we don't have them. This only begins to tell the story. I hope this helps.

Also, your a/f ratio is altered during the running of the vehicle, and many times per second. With inputs such as CKPS, CPS, TPS, MAP, MAF, O2, and KS coming in at anywhere as high as 360,000 signals per minute (60tooth at 6000rpm), the computer is altering critical injection and ignition events constantly. If you change the VE, or other parameters of the engine that would effect O2 readings (rich/lean), the computer changes the long term and short term fuel trims to adjust to these conditions. Changing your exhaust doesn't change this, it just changes the efficiency at which it operates at given rpms (as some are better high than low).

I had no idea how complicated the physics of simply getting the exhaust out of an engine were. So basically, some shade tree mechanic tinkering with his exhaust system has a 99% chance of making it worse. Especially if that car is designed with performance in mind. Such as an exhaust system that is completely encased in insulation with a heat shield on top of that.

No wonder exhaust system mods are so hotly debated. Sounds as complicated as nuclear science, yet any joe blow can claim to know something about it.

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.

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.

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.:thumbup:
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.

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?:confused: A 3" exhaust on a 1.9 TDI could increase mpg at light engine loads?

science?
 

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.

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.

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.

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.

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

From that ehow article it is not saying that turbos like back pressure it is saying the pressure created from the restriction that is the turbo turns the turbine to create power. The article is badly worded.

A turbine blade is the same as a wing. A wing generates lift by a pressure differential. The larger the pressure differential, the more lift is created. For the turbine this means that there will be a larger amount of torque on the shaft of the turbo applied by the turbine. The impeller will be able to apply a larger force on the air forced into the intake because of this additional torque input. More force, more air, higher efficiency.

Ohh man you just helped me aton even on my fastspire project (aka a wanna be mazda version of the crx) Dude thank you now I just gotta figure out what exhaust i really want on it now.

Does straight pipe causes higher MPG?
 

Hi Guys,
Has anybody gained higher MPG by switching to straight pipe in case of diesel engine?

I have an 1999 1.9TDI Toledo and I want to maximize its MPG. I'm not a race driver so don't bother with HP earning.
Thanks in case of any feedback from You. :)

My best result is 3,4L/100km (measured on gas station + GPS)

It could help slightly since the turbo will not have as much back pressure and the car will be slightly lighter. I would not do it unless you are needing to replace the exhaust.

If you want to make changes for better MPG I would check into replacing the 5th gear with the 6th from the 6speed that came our in the mid-late 2000s. I know it has been done on the Golfs and I believe it can be replaced with out removing the trans.

The other thing I would check into would be a tune. Tuning the PCM/ECU will give more power but you don't need to use it. In the lower loads and RPMs the timing is better set and fueling adjusted. Often the curve for the Turbo is better set reducing turbo lag reducing the time you need to keep your foot on the go peddle.

Many thanks for your answers and advice :)

The present set of exhaust system would need a repair or at least fix it cause the 'middle muffler' a bit close to the road. Here in Hungary the catalisator is a very needed thing so I think it is empty. So maybe I can try the straight pipe program. MOT will be 1,5 year later. ;-)

Final gear swap. Hmmm. It would be nice but I'm not a car mechanic so I must find somebody to do it for me. All I know that presently at speed of 90km/h the RMP is slightly over 2,000.

There is a chip tuning on the engine (I bought the car with it, but I think it is many set for very high performance cause it is very strange that at low speed where my old 8v Twingo (with 54HP on her petrol engine) happily goes in gear 4 this Toledo prays for shifting back to 3rd gear. So I will go for another chip tune for FE.
Have a nice dayend :)