Help designing a downpipe
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Scooby Newbie
Joined: Jul 2019
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From: Essex
Help designing a downpipe
I’m looking to design and build my own down pipe for a Jdm hatch sti. Ive done so much reading up on open vs divided vs divorced and people saying there is a difference but it depends on a few different things.
Now, I can understand that depending on what turbo you’re using the bell mouth seems the best option vs the divider type down pipe due to what the back of the turbo looks like ie the vf35 has an open back where the divider sits so I can’t see that it would make much difference with just that thin divider over the open mouth down pipe.. verses the back of the vf49 having two separate compartments separated by a physical wall and gasket for turbine and wastegate enabling you to actually separate turbine and wastegate properly.. to create pipework that mimics an ewg if you like.
What I’m considering building is a sports cat downpipe where the turbine will be fed into the sports cat via a 2.25/2.5 tube and the wastegate into a separate similarly sized pipe that will enter back into the exhaust bypassing the cat in the bottom of the downpipe theoretically dividing the flows of gases and mixing them further down the exhaust where turbulent air shouldn’t be as much of a problem?
the idea is to lessen the restriction of the cat by only using it for the turbine side of the exhaust which should still enable it to pass an mot as the waste gate shouldn’t open (letting none catted gases from the wastegate into the exhaust) while sitting there not under any real load from just being rev’d in the mot bay..
this in turn would relieve any back pressure from the back of the waste gate and possibly give better control of the wastegate??
thoughts?
theoretically this should be the optimum use of the cat and wastegate shouldn’t it?
Now, I can understand that depending on what turbo you’re using the bell mouth seems the best option vs the divider type down pipe due to what the back of the turbo looks like ie the vf35 has an open back where the divider sits so I can’t see that it would make much difference with just that thin divider over the open mouth down pipe.. verses the back of the vf49 having two separate compartments separated by a physical wall and gasket for turbine and wastegate enabling you to actually separate turbine and wastegate properly.. to create pipework that mimics an ewg if you like.
What I’m considering building is a sports cat downpipe where the turbine will be fed into the sports cat via a 2.25/2.5 tube and the wastegate into a separate similarly sized pipe that will enter back into the exhaust bypassing the cat in the bottom of the downpipe theoretically dividing the flows of gases and mixing them further down the exhaust where turbulent air shouldn’t be as much of a problem?
the idea is to lessen the restriction of the cat by only using it for the turbine side of the exhaust which should still enable it to pass an mot as the waste gate shouldn’t open (letting none catted gases from the wastegate into the exhaust) while sitting there not under any real load from just being rev’d in the mot bay..
this in turn would relieve any back pressure from the back of the waste gate and possibly give better control of the wastegate??
thoughts?
theoretically this should be the optimum use of the cat and wastegate shouldn’t it?
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