The best off the shelf manifolds that are readily available probably are the Full Race manifolds i personally like the duel gate one best if going twin scroll but if designing your self i would much rather use steam pipe instead of cast stainless
this next bit of info is taken off another forum so i suppose i should quote it
"To build a good split pulse 4cyl turbo manifold takes a fair bit of knowledge in turbo specification, TURBO manifold design, fabrication skills, knowing what the right materials are and where to source them.
Completely divided split pulse turbo systems can work very well in high performance applications when done correctly but it is a lot easier to get these designs wrong over an open collector manifold design or equalised split pulse manifold design.
All three of these systems are different by design and have different requirements in manifold design, wastegates, turbo design & turbo specification.
The true completely divided split pulse systems are built to the firing order of the engine and keep the exhaust gases divided from both half’s of the manifold and exhaust housing scroll all the way to the turbine, and divided all the way to the valve on the wastegate or two wastegates are used.
(The twin wastegated 4cyl Full Race manifolds are a fine example of this system)
Equalised split pulse systems are built to the firing order but both half’s of the manifold are equalised. On after market manifolds this is usually done at the wastegate collector.
This is the most common split pulse manifold design.
(Your factory cast SR20DET manifold is of this design)
Open collector systems are the most common high performance manifolds.
They are exactly as they sound. They have an open collector and open exhaust housing.
Simplifying the requirements for the completely divided split pulse system;
Keeping the same compressor size. The turbo will perform better with a larger turbine and bigger exhaust housing A/R.
Not all turbo manufactures offer different turbine trims so most opt only for the bigger A/R housing. (I know of a turbo manufacture that does offer many different turbine trims. Wink Wink) LOL!
With a true completely divided split pulse system more wastegate is needed.
Where a single 44mm gate might have worked fine with the other systems on a decent power high performance 4cyl. You’re going to need a single 60+mm gate or two 38+mm gates with a completely divided system.
(The twin wastegated 4cyl Full Race manifolds are a fine example of the manifold design required for this system)
All the above requirements need to be addressed in these systems. Even if one of the requirements is not 100% correct it will not work any better than the other designs and/or could hinder performance."
this next bit of info is taken off another forum so i suppose i should quote it
"To build a good split pulse 4cyl turbo manifold takes a fair bit of knowledge in turbo specification, TURBO manifold design, fabrication skills, knowing what the right materials are and where to source them.
Completely divided split pulse turbo systems can work very well in high performance applications when done correctly but it is a lot easier to get these designs wrong over an open collector manifold design or equalised split pulse manifold design.
All three of these systems are different by design and have different requirements in manifold design, wastegates, turbo design & turbo specification.
The true completely divided split pulse systems are built to the firing order of the engine and keep the exhaust gases divided from both half’s of the manifold and exhaust housing scroll all the way to the turbine, and divided all the way to the valve on the wastegate or two wastegates are used.
(The twin wastegated 4cyl Full Race manifolds are a fine example of this system)
Equalised split pulse systems are built to the firing order but both half’s of the manifold are equalised. On after market manifolds this is usually done at the wastegate collector.
This is the most common split pulse manifold design.
(Your factory cast SR20DET manifold is of this design)
Open collector systems are the most common high performance manifolds.
They are exactly as they sound. They have an open collector and open exhaust housing.
Simplifying the requirements for the completely divided split pulse system;
Keeping the same compressor size. The turbo will perform better with a larger turbine and bigger exhaust housing A/R.
Not all turbo manufactures offer different turbine trims so most opt only for the bigger A/R housing. (I know of a turbo manufacture that does offer many different turbine trims. Wink Wink) LOL!
With a true completely divided split pulse system more wastegate is needed.
Where a single 44mm gate might have worked fine with the other systems on a decent power high performance 4cyl. You’re going to need a single 60+mm gate or two 38+mm gates with a completely divided system.
(The twin wastegated 4cyl Full Race manifolds are a fine example of the manifold design required for this system)
All the above requirements need to be addressed in these systems. Even if one of the requirements is not 100% correct it will not work any better than the other designs and/or could hinder performance."
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Originally Posted by Coheed 
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