The Absolute Best: PART I~

In these next few entries we are going to walk through the DOC Race manifold processes to help you choose the proper turbo manifold for your project to gain the best results.

Starting a turbocharged project that is solely performance oriented can be very difficult considering the amount of parts available in todays aftermarket, “forum engineers” and even general project decisiveness. There are a lot of areas to address in a build like this, so it can be easy to get sidetracked in whats necessary to execute something that performs like intended. With the amount of information out there like the already tried and trued setups, you shouldn’t have an issue building a setup that mechanically performs with most popular platforms. Most factory turbocharged Japanese engines can handle more then what the factory turbocharger sizes are capable of; even larger frames. The more “streetable” build, less camshafts, possible valvetrain and clutch systems are capable of 2x there factory duties. With some general goals in-mind we can help to put these scratch paper plans into a reality through our catalog and parts avenues.

People are usually unsure of what to look for when shopping for a turbo exhaust manifold besides what they read someone else had in Super Street or on the forums. These may be quality parts, but not the proper fit for your projects performance. The first thing to consider is the overall goal of the build. Even though the best manifold builders in the world will always take the time in assembly and welding of each and every given design, there are small differences between each design that aid in extracting the most from your setup.

When you put thought into your build, the heart of your turbocharged setup (aside from the actual engine internals and tuning) will be the exhaust manifold. Creating the best spool and having optimum boost control are two thoughts that should be evaluated when stacking parts for your beast. It’s amazing how uninformed people are that are stepping into the turbocharged game. I feel one of these reasons is that the “JDM” engines are already so efficient and for the most part bullet-proof so peoples “half-assed” setups STILL do work to the point where they don’t realize what has been left on the table.

DOC Race exhaust manifolds have countless hours of R&D to attain the best results. When developing parts we use as many resources as we can to get the most from each part. Being a smaller company considering the Race Part Developers of today, we haven’t got any better results then physically running our parts on race cars. Computer programs can account for a lot of things in design, but in a turbocharged system we have learned and adapted so much more with our real-world experiences. Turbochargers get unbelievably hot and with the expansion of gasses and contractions of metal there isn’t any better evidence then trial and error to really push the limits of components and materials.

We are fortunate being able to work along side some of the best tuners, engine builders and most importantly crazy maniacs who are willing to try the untried to gain the most amazing results that would have never been thought possible. These factors are what make D.O.C.’s knowledge in manifold building extra ordinary in this industry and complete confidence of our products abilities. From day to day use all the way up to extreme conditions we are learning every single day of how to make things better.

DOC Race Manifold Process: STEP 1

When building one of our production exhaust manifolds we generally start with one of our hand-built Stainless Steel Merge Collectors….

With so many different applications, each of our merge collector designs are completely different from eachother. Not just tubing size but actual merge angle to collector length to T flange entrance. All of these factors are key to properly using exhaust pulses even in an Open T Flange design.

Another very important factory in the Merge Collector design is which desired wastegate is going to be used. This may change our collector design a bit even in the same applications just a different gate. Positioning of the outlet in the merge will aid in wastegate control which in-turn allows more aggressive boost controller setups and fitment.


Manifold tubing size. This is something that is also decided when building the merge collector because it’s generally built according to the diameter and wall thickness from flange to flange of the manifold aside from scavenged headers that are usually on Naturally Aspirated setups for precise header back pressure tuning. Most of our production manifolds, we use a schedule 40 wall 304L stainless steel tubing in either 1″ 1/4 or 1″ 1/2 diameter depending on port size and horsepower goals.

Also considering tubing size, this is something that needs to be accounted for on the wastegate outlet tube to get the proper amount of exhaust volume through the chosen wastegate. For example we use a larger diameter tubing on the MVR (Tial 44mm V-band) outlet then the 38mm (Tial MVS or 2-bolt) outlets for the larger diaphragmed gate.

We will continue with the manifold build process in Part II going into purging, porting and other important aspects of manifold design…


One thought on “The Absolute Best: PART I~

  1. Pingback: The Absolute Best: Part II~ | DOC Race

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