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Old 05-27-2010, 10:34 AM   #31 (permalink)
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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.

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Old 05-27-2010, 10:48 PM   #32 (permalink)
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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.
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Old 05-28-2010, 02:27 AM   #33 (permalink)
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Quote:
Originally Posted by autoteach View Post
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.
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.
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Old 03-25-2022, 06:24 AM   #34 (permalink)
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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)
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Old 03-28-2022, 09:11 AM   #35 (permalink)
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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.
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Old 03-28-2022, 03:14 PM   #36 (permalink)
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Quote:
Originally Posted by Phantom View Post
...

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

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