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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.

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

See 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 it....it'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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Tech Tips Part II Buffing the Plenum Extension Trans Am and Other Models

After you get your Plenum polished up the next area of concentration would be the Plenum Extension or Distributor Cover that attaches to it. This piece is plastic. If you were to use the stock plastic piece the best you could do would be spray it with a shiny silver paint like Eastwood Aluma-blast.....but there is a better alternative. Go to GM Dealer and order or buy the following part numbers:

GM P/N 10108425 Aluminum Plenum Extension $ 19.50 GM P/N 14082425 Screws (for plenum extension) $0.42 x 3

This is the Plenum Extension from the Corvette models and it is aluminum. Follow the same procedures as you did on polishing the plenum. Be sure to get the three screws because they are different than the ones that hold the plastic cover.

Painting the Grooves in the Plenum and Extension

Now that you have your plenum and extension buffed out it sets off the finish if you repaint the grooves. You can choose any color to match your car or in my case I used Eastwoods Under Hood Black....which is a semi-flat.

I did my extension first with modelers paint and a small paint brush. This looked pretty good from straight down but what I noticed is the sides of the grooves were not covered. You rarely look at your plenum straight down from the top but actually view it from the sides. This makes the "sides" of the grooves the most important part of the visual so I came up with this idea.

The first thing we must do is clean the grooves. I use acetone and a q-tip to remove the buffing compound build up from the polishing process. Next I shoot some compressed air to clean lint and any debris.

Use masking tape to establish a stop line for the grooves. Always use commercial grade painters masking tape for good results.

Repeat a guideline for both sides and don't forget the back, it is still cast and cleaning black from the cast would be difficult.

Wrap a tight weaved cloth (t-shirt or hankerchief, not towel) tightly around your finger. Put some oil on the cloth on top of your finger and blot this against somewhere else on the cloth. Then while keeping cloth tight rub oil onto the top...... NOT in the grooves. This will keep the paint from sticking to the top. Do it a couple of times. Go ahead and cover other non-spray areas with paint paper or newspaper.

Spray a mist coat from the left, wait a couple of minutes and repeat from the right, then the back, then a coat straight down from the top. Wait a few minutes and check the grooves for coverage. Repeat top coat if necessary. You may remove the paper to make the piece easier to move.....pull tape towards you. But do not remove the guideline tape for about 12 hours.

When you pull the tape off be sure to pull towards you or away from plenum.

I put some acetone on the rag and stretch it tight to remove black paint from the plenum ribs....just go slow here. I retape my stop line and fill in details with a brush and let dry.....you just have to play with your stop lines since the grooves are not deep here.

I do a quick re-buff with white rouge to remove handling traces and to buff out natural stop lines in the grooves and this gives you the completed project.

Here is a top view of the completed project.

[ Back to Part I - Polishing the Plenum ]

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