exhaust
-
carmadaaron
- Bling Bling Diamond Member
- Posts: 4350
- Joined: Fri Mar 12, 2004 8:55 pm
- Location: Scotland
-
carmadaaron
- Bling Bling Diamond Member
- Posts: 4350
- Joined: Fri Mar 12, 2004 8:55 pm
- Location: Scotland
I know you won't like to hear it but the optimum exhaust *is* the VW one. There are many hours spent using fluid dynamics analysis and lots of coffee by the boffins at VAG.
Stick anything else on and you will have a less than optimal result. The general consensus is that bigger is better, the more easily it can push gasses through the better, right? You'd be wrong - well for general driving anyway. The response of the exhaust to different frequencies, its back pressure under different circumstances is important for Torque and Driveability. Don't forget Torque at lower engine RPM is very important. 16V engines really struggle for torque because of this reduced backpressure.
Just as a side note, remember murray walker trying to drive that formula one car? Even though it had 830BHP at 17K RPM he couldn't get it going because it has virtually no torque at all at idle which is 5 - 7000 RPM!
Don't forget> Torque * Speed = Power!
Stick anything else on and you will have a less than optimal result. The general consensus is that bigger is better, the more easily it can push gasses through the better, right? You'd be wrong - well for general driving anyway. The response of the exhaust to different frequencies, its back pressure under different circumstances is important for Torque and Driveability. Don't forget Torque at lower engine RPM is very important. 16V engines really struggle for torque because of this reduced backpressure.
Just as a side note, remember murray walker trying to drive that formula one car? Even though it had 830BHP at 17K RPM he couldn't get it going because it has virtually no torque at all at idle which is 5 - 7000 RPM!
Don't forget> Torque * Speed = Power!
-
moynas
- Silver Member
- Posts: 403
- Joined: Fri Sep 19, 2003 11:53 am
- Location: colchester essex
- Contact:
Have to say forget what all these geeks say! (geeks run the country and look at the state of it) cos my magnex with its 69mm cat back pipe with 6x4 exit has made my car feel so much more responsive and pull away is quicker! take the cat out open the pipes up and let it roar!
if a scooby can run 3" pipe work why cant a gti polo run 69mm????
if a scooby can run 3" pipe work why cant a gti polo run 69mm????
'lo chaps
I'm gonna go for something that no-one else has brought up yet
and follow the lead of my sister's blokey. His Mk4 16v has a powerflow cat-back system which is just a straight-thru stainless exhaust styled so that it hides behind the rear valance out of sight just like VW intended
I can't decide on a suitable backbox design so thats what I'm gonna have done when I scrape a bit of spare cash together and on the plus side it'll sound much better than standard
I'm gonna go for something that no-one else has brought up yet
and follow the lead of my sister's blokey. His Mk4 16v has a powerflow cat-back system which is just a straight-thru stainless exhaust styled so that it hides behind the rear valance out of sight just like VW intended I can't decide on a suitable backbox design so thats what I'm gonna have done when I scrape a bit of spare cash together and on the plus side it'll sound much better than standard
Erm.. working in IT makes me a geek and I want to change my standard exhaust - am I an exception then?moynas wrote:Have to say forget what all these geeks say! (geeks run the country and look at the state of it)
-
polo2k
- Bling Bling Diamond Member
- Posts: 3297
- Joined: Tue Dec 10, 2002 1:01 pm
- Location: Swindon
- Contact:
"Hi pigeons this is a cat!"
well i use a cat back madac with a gorgeous deep sound. there not available in the uk so youll have to import. thats ot hard to do though.
now while were on the subject of if they work of not...
a standard exaust is designed to a brief with very wide criteria, it must be quiet, ling life, economical. etc. when changing exaust some of theese factors can be changed. for example the larger the bore (to a certain extent) the greater the scavenging effect actng upon the exaust ports, with a better scavenging effect you get less dirty air in the cylinder so combustion is cleaner and more efficient. the lower back presure can cause responsiveness problems at low revs and the gas velocity within the exaust is lower and there fore holds more kinetic energy and therefore more inertia, this must e overcome before the engine can really breathe. the lower back pressure can work in certain situations to a great advantage, for exam[ple i have reworked my throttle body (knife edged) and opened up and alligned all the inlet and exaust ports so rather than there being a pressure depression where the new exaust starts the gasses are free to accelerate throughout the exaust freely which works in conjunction with the modified inlet air flow meaning there is a lesser amount of resistance throughout the induction and exaust sides of the engine. the reason why some people find that the new exaust can loose you power is that it created a lower pressure in the exaust which mismatches the inlet and cause mixture problems, this problem is magnified because when the gasses flow past the O2 sensor the molecules are more sparcely dispearced and there for when the sensor takes its gas sampole it is sampling too few molecules of the components of the gas and this causes an in accurate reading, which in turn can cause performance to deteriorate. in some cases it can help to allow the engine to go into safe mode by unplugging an O2 sensor so that the factory defaults are used.
any q`s then ask away
well i use a cat back madac with a gorgeous deep sound. there not available in the uk so youll have to import. thats ot hard to do though.
now while were on the subject of if they work of not...
a standard exaust is designed to a brief with very wide criteria, it must be quiet, ling life, economical. etc. when changing exaust some of theese factors can be changed. for example the larger the bore (to a certain extent) the greater the scavenging effect actng upon the exaust ports, with a better scavenging effect you get less dirty air in the cylinder so combustion is cleaner and more efficient. the lower back presure can cause responsiveness problems at low revs and the gas velocity within the exaust is lower and there fore holds more kinetic energy and therefore more inertia, this must e overcome before the engine can really breathe. the lower back pressure can work in certain situations to a great advantage, for exam[ple i have reworked my throttle body (knife edged) and opened up and alligned all the inlet and exaust ports so rather than there being a pressure depression where the new exaust starts the gasses are free to accelerate throughout the exaust freely which works in conjunction with the modified inlet air flow meaning there is a lesser amount of resistance throughout the induction and exaust sides of the engine. the reason why some people find that the new exaust can loose you power is that it created a lower pressure in the exaust which mismatches the inlet and cause mixture problems, this problem is magnified because when the gasses flow past the O2 sensor the molecules are more sparcely dispearced and there for when the sensor takes its gas sampole it is sampling too few molecules of the components of the gas and this causes an in accurate reading, which in turn can cause performance to deteriorate. in some cases it can help to allow the engine to go into safe mode by unplugging an O2 sensor so that the factory defaults are used.
any q`s then ask away