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The new 3"" system now a small sound clip
animal:
Don't take it as gospel. It makes sense in my head and I think I've managed to get it down properly. I just wanted to try and dispel this commonly held misconception that back-pressure is needed for torque. It's all about exhaust gas velocity as low RPM.
jonnyc:
--- Quote from: animal on February 27, 2009, 12:42:12 pm ---Don't take it as gospel. It makes sense in my head and I think I've managed to get it down properly. I just wanted to try and dispel this commonly held misconception that back-pressure is needed for torque. It's all about exhaust gas velocity as low RPM.
--- End quote ---
Very true, but as far as I understood there was little to no scavenging effect on a tubo car post turbo in the exhaust??.. Only turbulence caused by the wastegate opening if you have an internally gated exhaust..
The reason you can get away with a larger diameter downpipe that then steps down to a smaller diameter later on in the exhaust is that the exhaust gasses exiting the turbo are much hotter, ie, more velocity and as they cool going down the exhaust they need less space..
animal:
Yeah, the rules are different for turbo engines. I forgot until I was half way through writing that the GTi is forced induction (doh!) which is why I added the bit at the end about it being less of an issue on the GTi. But yes, there will be a change in density as the gas cools so the change in diameter wouldn't be the end of the world. Although at the same time, any change in the pipe like that would still cause turbulence in the gas flow which effect the rate of flow?
jonnyc:
--- Quote from: animal on February 27, 2009, 12:56:57 pm ---Yeah, the rules are different for turbo engines. I forgot until I was half way through writing that the GTi is forced induction (doh!) which is why I added the bit at the end about it being less of an issue on the GTi. But yes, there will be a change in density as the gas cools so the change in diameter wouldn't be the end of the world. Although at the same time, any change in the pipe like that would still cause turbulence in the gas flow which effect the rate of flow?
--- End quote ---
Yeah, thats what I mean, you can get away with a step down but its certainly not ideal. You need the smoothest flowing system possible with the smallest silencers too, big silencers, even if they have a straight through design end up being huge expansion areas where the exhaust gasses will loose heat and therefore velocity..
The most critical part is having the optimum diameter. 70mm for K03 / 76mm for K04 seems to work well.. Although I think 70mm on a K04 also works well, but you will loose some potential top end power..
MAT ED30:
sound clip of it on mine
http://www.mk5golfgti.co.uk/forum/index.php/topic,18320.0.html
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