The Absolute Best: Part II~

In Part 1 of the D.O.C. Manifold building process we talked about the merge collector and also the tubing size used for various manifold applications. In Part II we are going to cover some other areas of building and finishing.


Controlling temperature while welding is something that is very important to creating a consistent and solid weld joint. Through this process, DOC Race materials are heat treated and scuffed. This is what gives the DOC Race manifolds there unique glow and heat transfer color up.

Ben’s EVO 8 With a few Heat-cycles:

DOC Race Supra Manifold:

Another factor in having strong weld joints is back-purging. This is something that isn’t completely necessary to do, but considerably important for the inside portion of the weld joint. By purging the tube that is being welded, the argon gas that is pressurized inside during welding will aid in controlling push through and also any impurities that may occur during the weld. Purging is a must with some materials even going as far as chamber purging with metals like Titanium that require a lot more preparation and care for a proper weld joint.


Fitting and sequence. In raw form, D.O.C. manifolds are fit together with tacks and freshly treated materials. Having clean materials and very tight fitting joints is important so that your welding processes are not going to have weak points due to off-tangent tubes or gaps. Once the runners are properly fit to the cylinder head flange and merge collector, they are broken off and welded in a sequence accounting for shrinkage and re-fit for the final flange and merge welds. As we talked about in Part I, it is going to be very important to decide what manifold design is needed for your build so that we use the proper tubing size and cut the proper merge collector for your manifold.

Sometimes people think that “hey I have a T3 manifold I need you to cut that flange off and put a T25 flange.” This isn’t something that we do here, we cut the merge collector according to turbo inlet size and the T flange opening so that the proper flow characteristics are balanced through the entire manifold. You may be able to add a T4 flange to a T3 collector and run it; but this will potentially restrict flow since we have a completely different merge collector design for our T4 layouts in-turn changing runner routing and fitment tolerances.


Manifold Porting. Once the runners have been welded up in there necessary sequences, they are re-fit and then welded to the merge collector and head flange. After this process is completed we then port the manifold to clean up any possible burrs and also keep good exhaust transitions into and out of the manifolds flanges. In some cases customers have very aggressive “Race Port” cylinder heads that now have larger outlet ports and they choose to do a port match to the exhaust manifold and gaskets to keep that smooth transition.

Beginning Port Process for 2JZ Manifold:

Completed 2J Manifold Less Wastegates:


Now that the manifold has been welded and ported, the wastegate outlet(s) need to be added to the merge collector. There are many different wastegate outlet designs through our catalog, choosing a proper wastegate according to your setup is very important to having proper boost control. Having ideal wastegate control will allow you to setup your boost controller more precisely giving “ramping” to your boost curve and also not having high RPM “boost creep”.

Another factor in wastegate control that is overlooked, is the fact that sometimes people are looking for a “street-car” setup or street-tune generally on pump-gas and they desire low boost levels. When looking for the possibility of low boost levels, a very good wastegate duty is needed so that the gate can exhaust the un-needed flow that the turbocharger is producing in-turn giving you a Low Boost Level. A general example of this is if there’s 50psi of exhaust gas and you only want to use 10psi of this exhaust, the other 40psi will need to be expended through the wastegate. It is quite a bit more complicated then that, but that should give you the generally idea of gate duties.

When building the wastegate outlet there are two sizes that are the most common. We prefer the Tial wastegates due to there experience and proven performance over the years. The Tial MVS wastegate is a 38mm V-band wastegate that also has water jackets for potential EGT issues that may arise.

The next step up would be the popular Tial MVR wastegate. This a 44mm wastegate that also has the watercooled option and will allow a higher volume of exhaust pulse control due to it’s larger size then the MVS.

Some of the older wastegate designs are still good to use, a lot of people still run the old style Tial 38mm gates that are a 2-bolt design. These don’t handle quite as much duty but are still a great performing wastegate.


There are other companies out there that make quality gates as well and will still fit with our standard 38mm and 44mm V-band flanges such as the Precision and Turbosmart gates.

That pretty much sums up the production of a DOC Race manifold, hopefully you have found this as knowledge in helping you put your turbocharged setup together. If there’s any possible questions you may have that haven’t already been covered, please visit the DOC SHOP for more details. We have tons of Turbo Compressor maps and many different applications already available for turbo manifolds.

One thought on “The Absolute Best: Part II~

  1. Pingback: DIY manifold - Page 6 - Miata Turbo Forum - Home to the Turbo Miata

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