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DIY Intake Manifold Basic
Written by Ryan K.

Materials:
1) 12" of half-round plenum extrusion from RossMachineRacing.com (RMR - 043)
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2) Two universal half-round vacuum endcaps from RossMachineRacing.com (RMR - 048)....one normal and one not tapped
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3) Custom cut stock TB flange (from Brad D.)
4) 12" of 2.5" ID 6061 aluminum straight pipe
5) 1/4" NPT brass barbed fittings (blow-off valve, boost gauge, fuel pressure regulator, boost controller signal and brake booster) from McMaster.com
6) Nuts and studs from NAPA to hold plenum to stock upper runners
7) 2 sets of intake gaskets for test fitment/drawing/grinding and final installation

Tools:
1) 28 degree inverted taper carbide burr from American-Carbide.com (2152002)
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2) Die grinder
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3) Several die grinder misc. wheels (round stone, cone, etc)
4) 40, 220, 400, 600, 800, 1000 grit sand paper

I first test fitted the half round plenum on the stock upper runners in the engine bay to make sure everything will fit. Then I sketched an outline of the gasket onto the new plenum.

Tech

After that, I started cutting away with my die grinder to match the gasket outline. So basically you match the gasket on both the plenum and the upper runners flange. Once its close to the edges, then use the inverted taper carbide on the die grinder (facing the mounting plate of the plenum).

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Make the entry really smooth. Sand the ports with sandpaper and make sure there are no sharp edges or burrs.

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Once the ports are done, drill out two small holes which line up with the holes on the mounting flange of the upper runners. Basically this will help you run 2 bolts through so you can put a nut on the other side and then the plenum will be fastened to the runners. After that, drill out the rest of the holes through the top of the mounting flange (so the drill bit doesnt move around) and make sure to use the corresponding drill bit size for the tap size you are going to use. Once all the holes are tapped, run the studs into the plenum and tighten nuts onto them...For the throttle body, just mark its spot in the middle of the front end cap, draw your 2.5" tube onto it and cut that hole with a hole saw. Then its handy to have the 2.5" tube welded onto the end cap and the TB flange welded onto the tube so you can smooth the entry of the endcap port into the plenum...Once thats done, then you can have both endcaps welded onto the plenum.

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Then just run your barbed fittings in with thread tape. Then put your gaskets on and install it.

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Other things to consider:
- Making a bracket for the TB cables. Can be as easy as running a longer bolt through one of the TB mounting holes and bending a bracket to fasten on the other side of the bolt. And then you cut a "U" shape so that the throttle cable can lock down on
- Whether or not you want the IACV...You can make a port for it on the plenum or get the remote mount IACV from Xcessive and tie it in that way

Modification Justification:
I know this plenum isn't the most efficient design out there, but I'll explain the reasons why I think it is beneficial. The main reason I wanted something like this, is that the stock plenum is vulnerable for boost leaks...And boost leaks/less air = less HP....I tapped out the PCV re-entry ports on the runners to 1/8" NPT and put plugs in there. Now I no longer have to deal with leaks there or at the EGR or IACV which I no longer have. It also elminated 5-6" of runner length which the stock lower plenum has. Then some people ask "why arent there velocity stacks?" The stock plenum didnt have any and the port entry was radiused so I figured I would do the same.

Total costs ~ Less than $200

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