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Yo! Can anyone offer an explanation as to why increasing diameter of the exhaust decreases torque in an Engine? I understand that larger exhaust decreases back pressure, but what actually happens inside the cylinder head that accounts for power\torque loss? I'm losing sleep trying to figure this one out
. Thanx!
 

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Try this link out. Mentions exahust pulses being closer together since the pipe is restricted which results in more torque.

Not sure I 100% understand that sentance, but it seems logical enough to me.
 

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Basicly larger diameter results in slower gas flow which is bad... Too large diameter also decreases/diminishes the scavenging effect and causes further performance degration.

The aim of an exhaust system (apart from sound reduction) is forming a system that queues the gas pulses one after another to form a "near vacuum" environment for the cylinders to push the exhaust gasses out easily...Otherwise, everyone would be running open headers...
 

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Thought I would mention that I just replaced my Borla(2 1/2") system with the Flowmaster (2"). My only mod is an ITG drop in filter and the stock airbox mod. The Flowmaster out performs the Borla and I got an instant 2 mpg increase.
 

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Well, I use 2.3" (60mm - the pipe size closest to 2.25" available here) custom exhaust all the way, from race header flange to the tip, and I am quite happy with the size...
 

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The only thing that really "happens" inside the cylinder is that the slower exhaust flow means less scavenging, so some of the engine's power is lost because it needs to pump the air out. Smaller pipes give faster flow, so the scavenging effect is increased. However, you get higher backpressure, which counteracts this. You have to balance everything to optimize the system.

Oh, and bigger exhausts don't really decrease torque. They might decrease torque at a point (usually lower in the rev range), but all they really do is move the torque peak/high torque range around. The bigger the pipe, the higher the engine will need to rev to hit the peak. It's possible for the pipe to be so big or small that you never hit its sweet spot.
 
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