19-07-2012, 05:48 PM
The optimum length for a turbocharged engine is straight out the turbine wheel...
There's no pulse tuning or resonance to scavenge the cylinders of their gasses past the turbine wheel.. Before the turbine wheel if you have equal length runners you might see a slight gain, but obviously the turbine wheel is what causes the back pressure...
It's really a myth that an engine needs backpressure to make *power*... It needs the least amount of backpressure to make it's *PEAK* power - wherever that is in the RPM band, but as always with engines, it's a compromise, you want the backpressure there to prevent the valve overlap from sending half the mixture out the exhaust at low RPMs to keep up the midrange torque, but unrestrictive enough at high RPMs to allow the valve overlap to keep gas velocity up to let inertia keep pulling the gasses out the cylinders after TDC combined with the pulse tuning of the exhaust.
When gasses exit past the valve, their velocity is very high, the higher the engine speed, the more the velocity of the gas goes up... When you send a gas very quick through an orifice, even after you stop the force that caused the gas to want to exit the cylinder (the piston returning back up the bore...) it'll want to pull some extra gas with it - the inertia effect...
There's no pulse tuning or resonance to scavenge the cylinders of their gasses past the turbine wheel.. Before the turbine wheel if you have equal length runners you might see a slight gain, but obviously the turbine wheel is what causes the back pressure...
It's really a myth that an engine needs backpressure to make *power*... It needs the least amount of backpressure to make it's *PEAK* power - wherever that is in the RPM band, but as always with engines, it's a compromise, you want the backpressure there to prevent the valve overlap from sending half the mixture out the exhaust at low RPMs to keep up the midrange torque, but unrestrictive enough at high RPMs to allow the valve overlap to keep gas velocity up to let inertia keep pulling the gasses out the cylinders after TDC combined with the pulse tuning of the exhaust.
When gasses exit past the valve, their velocity is very high, the higher the engine speed, the more the velocity of the gas goes up... When you send a gas very quick through an orifice, even after you stop the force that caused the gas to want to exit the cylinder (the piston returning back up the bore...) it'll want to pull some extra gas with it - the inertia effect...
