Tech Tips
Buffing the Plenum

Trans Am and Other Models

Once you have a
few basic supplies polishing the aluminum components on your car is one of the most satisfying, inexpensive modifications you can achieve. The Intake Plenum is the most visible component under your hood, followed by the runners. The polishing of these components will add the finishing touches to your engine bay. If you intend on porting and polishing your plenum it is recommended you port the plenum first. See my article on this site Porting Your Plenum.


You will need a drill, sander and dremel tool.

Sanding roll, metal cutting taper, metal cutting drum, sanding taper are the bits for your dremel that will make life easier.

Wet or Dry Sandpaper: 180/320/400
Steel Wool: #00 & #0000

Buffing Into Article for proper selection of the following:
Several Buffing Wheels for Drill
Tripoli Polish Compound
White Rouge Polish Compound

Let's Get Started

The first thing we must do is smooth the grain of the plenum. We will start by removing cast marks with dremel and metal cutting bit.

After the cast ridges are cut away use sandpaper to smooth cut marks. This is the "rough draft" mode so just get close. Use electric sander with 400 paper to "level" off surface.

Here is another cast line and a cast square that can be ground away.

You are just wanting to get this area relatively smooth and blended to all the surrounding angles.

There are basically 4 flat planes to deal with. Areas 1 & 2 are flat surfaces that are angled right and left. Area 3 is the large flat surface on the top. Area 4 is the flat surface in the front that slopes downward. Area 5 is a special area that we will deal with in a moment.

Here is another angle of the flat surfaces we are dealing with. You will use the electric sander starting with 180 grit and finishing with 400, sanding until all the grain and cast marks are gone.

As we sand the flat planes down it becomes apparent that we will have two "odd" areas. There will be two little "eyes" that pop up in the front corners of the plenum. You may lightly sand these areas in preparation for polish if they don't bother you or you may go to another extreme.

You guessed it....I went to the extreme of radius grinding this area down removing the little eyelets. You must grind from all directions until the indention disappears. Use caution as to not thin the bolt hole area or cut into the runner gasket area on the left hand side. If you do not feel comfortable with this process it's best to leave it alone.

At this point I will try to explain a little phenomenon. As you sand a grainy cast metal down. First it smooths to an "orange peel" type look, then smooth to touch, BUT, it still will have a fine porous trait. You must take the finish a step further to get rid of almost unseeable pores or you will wind up with "shiny" but not brilliant. On small pieces I start with the Tripoli compound, but on this larger piece I do a test polish with Emery just to see where I stand. This is where you go "why am I doing this?"....stay with's worth it. My piece needs more sanding for perfection.

A few hours later and we be done........with the Plenum that is.


[ Click Here for Next Steps...Aluminum Extension Mod ]

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