ErikwithAK01

Good morning fellow Corvette enthusiasts Today I am making a DIY thread about how I did my exhaust filler plate, at the request of several local Corvette brethren over in the Pacific Northwest section of this forum

For a little back story, I decided I wanted one of these after modifying my exhaust some months back (I have the Flowmaster 80-series set, and did the exhaust-bypass mod to them) just to finish off the look on that part of the car. To my amazement, prices for these things were quite high I was NOT going to pay somewhere between $50 and $250 for something I could make out of an $8 piece of sheet stock, and materials I already had

MATERIALS I USED, the (*) indicates items I already had

10" x 5" sheet of 0.90" 6061 T6 aluminum sheet stock--------$8
3M 401+ green masking tape-------------------------------$4*
Scotch brite twist-lock ultra fine sanding discs, 3/4"---------$3*
Pale oil (or machining oil, WD40, whatever ya got)-----------$4*
3M double sided high density foam tape---------------------$30*
Valve lapping compound------------------------------------$3*
Drill press (although a Bridgeport, will be much easier to use)-*

Now for a little history on engine turning. Engine turning, also known as jeweling, damascening, perlee, guilloche, is a finishing technique consisting of repetitive, overlapping swirl patterns machined into a metal surface, to allow that surface to retain oil, or as a beautiful finish, for purely aesthetic reasons. Those among us keen on their history, will remember the Spirit of St.Louis had this finish quite famously applied to her engine cowling.

In the teens, and twenties, this finish was applied to parts on cars built by the very cutting edge coach builders of the time. Manufacturers that included Bugatti, Duesenberg, and Mercedes, among others. Only the best could afford the luxury of such a finish, due to it's labor intensive nature, and the relative skill a machinist must possess, for this technique was applied using ones calibrated eye. Therefore, this finish (done strictly in the traditional sense) is inherently NOT PERFECT!

Now I KNOW what your thinking, and YES, this can be done with a little computing skill on a CNC machine, but as I explained above, the pattern is not supposed to be absolutely perfect. It's the tiny factor of imperfection that shows that your piece is made by hand, and the reason that I do this myself, instead of buying pre-fab sheets.

ErikwithAK01

Now that the history lesson is over, lets get down to the nitty-gritty I did this the lazy way I used scotch brite discs with twist locks on the back, and used a chuck I had for my angle grinder, chucked up into my Bridgeport. This is most definitely NOT the traditional way to do this, and surely not the prettiest either. The traditional way, is to make a wooden dowel out of hardwood, and face it on a lathe so it's perfectly flat on the cutting face, then apply valve lapping compound to your work piece, and voila 30 bajillion hours later, you have what you want. This will create and esthetically superior finish, that is visually stunning, and has a certain three dimensional aspect to it, that only truly shines when done using this method, but it is incredibly labor intensive. The reason I chose the scotch brite pad method over this, is because this part will be under my car, and never inspected critically, or up close, so the tiny imperfections caused by the random, uneven cutting surface of the pads, like ghosting (where part of the previous jewel shows through in the trailing edge of the following cut) will not be as important to me as say something on my dashboard, or under the hood of the car. So it's not vintage Bugatti worthy but it is unique, and fun, TIME CONSUMING, and shows off the abilities of a skilled machinist.

So, what I did was polish my work piece to a high gloss. The reason you do this is so that small imperfections in the base material, or scratches deeper than your cutting depth, will not show up in the finished product. I also find that the finer the initial finish, the more illustrious the jeweled surface ends up. The next step is to mix a little fine valve grinding compound, with some WD40 in a dixie cup, and apply a thin layer of it at the beginning of each row, extending to the end of my part, so that I would not have to continue to apply it as I work. What I did, was start each row at the very edge of the piece, so that 100% of the pad would contact the plate, therefore I would have a very accurate starting point for each row as I continued. I then eyeballed each of my following facets to overlap the prior one by 50%. Now this is the tricky part, you have to try and get your cut time, and pressure, to be exact for each facet, otherwise you'll end up with facets here and there that break the pattern because they show up in one, or both overlapping layers. This will be noticeable in low light conditions, as well as break up the 3D effect of the finish (this is where that experienced machinist part comes in handy the most). I suggest you do as I do, and that is to find some material to practice on before you go gun-ho on your final product.

ErikwithAK01

A fine finish indeed Not to discourage anyone, but I must be honest with my work time. This 5"x10" piece of sheet, took me 2 hours to complete like I said, this is a VERY labor intensive process, that will test your patience, it is a bit of a lost art. That being said, I had time to kill, and a Bridgeport, so why the hell not!

Now that I had my completed product, I used a high quality tape to protect the finish, while I cut, and ground, and deburred the piece for final fitment. I like to use the 3M 401+ green masking tape, very specifically because this tape does not leave residue when removed, it has a very clean edge to it (good for painting cars with), and is not only chemically resistant, but also temperature resistant up to 250 degrees it gets the ErikwithAK seal of approval, my favorite tape by far. It is also thick enough to protect your investment from unclean surfaces, dirt, and grit, until your ready to apply it.

The part is smaller than 5"x10" so that I could cut out the final product from the best looking part of the plate. I made a template out of plain old cardboard laying around, and when I came up with a size that did not contact the exhaust tips as they leave the mufflers, and had a good height to it to completely hide the cargo hump, I pulled it off the car, and traced it onto the back side of my jeweled plate. I then used a cut off wheel (since my bandsaw apparently needs a new blade) to roughly cut out the shape, and used my bench grinder, and angle grinder, to achieve the final product. I also used a fine file to deburr the edges while the tape was still applied.

For the last part, I used a little rubbing alcohol to clean the vertical ribs on the cargo hump, and the back side of my plate. I then applied a strip of the double back tape to each rib, lined up my piece, and applied firm pressure for a few moments to activate the adhesive.

And there you have it! Probably the only engine turned exhaust filler plate on a C5 anywhere. I will get better pictures when I have my DSLR, these were done with my phone, and they don't do it justice.

c5arlen

A suggestion... Loose the teeny sway bar.... Go bigger and then smile bigger!

ErikwithAK01

Wwwwooooo! That's some thread resurrection right here my good sir

I did, sometime in 2017 Currently running C5 Zo6 springs, and C6 Zo6 shocks, Hotchkis bars front and rear. Gotta do new bushing one day though. She's beginning to wander on mountain highways.