Exhaust Sysytem Theory
10-24-2006, 01:40 PM
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Exhaust Sysytem Theory
Great description of exhaust theory...
Go about halfway down the thread and read...
http://my.is/forums/showthread.php?t=203395
10-27-2006, 03:22 AM
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i think the pipe diameter section is lacking... there is a very systematic way that you can determine the optimal diameter but the problem is that it doens't matter. pipe doesn't come in all diameters so unless you want a very expensive exhaust system made of custom diameter stuff it's pointless.
you have to choose a diameter that will match the maximum flow rate of your engine. having this sorted will give you the most top end. this does not mean biggest or open header because you need exhaust gas velocity which is the second requirement. so first... match max flow second maintain exhaust gas velocity. now you can give and take with these two opposing parameters. more torque constrict the diameter to increase exhaust gas velocity, more top end then open it up (but not beyond the critical point) to gain more mass flow.
usually for na cars opening it up isn't that beneficial. for turbo cars it's a different story. turbo cars encounter the unique problem that the mass flow is huge and there's gonna be a lag in the ramp of mass flow anyway. so more suble losses like transisions to larger diameters is of heightened importance. bigger is better for turbo cars but how to you get to the bigger is of critical importance.
case in point, an na engine is relatively low mass flow running an open header setup is as simple as just putting on enough pipe so that the exhuast gas velocity coming out of the cylinder head port is not compromised. some stacks at the top will help transision to the open atmosphere nad you're making good power.
for a turbo car to run a dump into atmosphere you'll have to firstly have a pipe that can handle the top end flow, secondly have a transision to that pipe that will not create a rapid expansion induced pressure gradient at the mouth of the turbine opening. so you have a stack leading to a pipe that leads to a stack for optimal flow.
these are just some of the considerations but it basically comes down to these two factors.
also removing cats will indeed get you power in both the evo and in subarus so whoever thinks that cats are great for power is delusional consider that these two cars are what drive the import scene at the moment. that said the power prolly doesn't justify the deviance.
you have to choose a diameter that will match the maximum flow rate of your engine. having this sorted will give you the most top end. this does not mean biggest or open header because you need exhaust gas velocity which is the second requirement. so first... match max flow second maintain exhaust gas velocity. now you can give and take with these two opposing parameters. more torque constrict the diameter to increase exhaust gas velocity, more top end then open it up (but not beyond the critical point) to gain more mass flow.
usually for na cars opening it up isn't that beneficial. for turbo cars it's a different story. turbo cars encounter the unique problem that the mass flow is huge and there's gonna be a lag in the ramp of mass flow anyway. so more suble losses like transisions to larger diameters is of heightened importance. bigger is better for turbo cars but how to you get to the bigger is of critical importance.
case in point, an na engine is relatively low mass flow running an open header setup is as simple as just putting on enough pipe so that the exhuast gas velocity coming out of the cylinder head port is not compromised. some stacks at the top will help transision to the open atmosphere nad you're making good power.
for a turbo car to run a dump into atmosphere you'll have to firstly have a pipe that can handle the top end flow, secondly have a transision to that pipe that will not create a rapid expansion induced pressure gradient at the mouth of the turbine opening. so you have a stack leading to a pipe that leads to a stack for optimal flow.
these are just some of the considerations but it basically comes down to these two factors.
also removing cats will indeed get you power in both the evo and in subarus so whoever thinks that cats are great for power is delusional consider that these two cars are what drive the import scene at the moment. that said the power prolly doesn't justify the deviance.
10-27-2006, 02:45 PM
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