Stainless Exhaust Overhaul cat-back decat resonator down pipe and turbo outlets

This article is part of the much longer, complete R32 Build Story. After dropping down the exhaust system, you're likely to notice that it's not exactly in the most pristine of conditions. After even one season, all the rain and dirt and heat cycling has caused it to become encrusted with dirt and grime. When you've just paid for a stainless steel exhaust system this might have you wondering what exactly you paid for! My system is the HKS Hi-Power Silent, made from 3.5" stainless steel.
Seeing the way mine looked, made me want to find out what could be done to improve the condition of the exhaust system. Although the dirt and grime really doesn't affect performance, and most likely no body will ever look under the car and say: "hey! that exhaust is filthy!", I still like to keep every part of the car in as proper condition as possible. So I decided to see how it would look after a few passes with a wire brush wheel, and I was quite pleased with what I discovered.
Polished axle-back pipe section
Polished muffler section
After only a few passes I began to see the so called "stainless" steel below the caked on grime. So I continued with the wire brush wheel all over the entire axle-back portion of the system. Next, I moved to sand paper, I started off with a very rough grit at first, eventually moving to a very fine grit wet/dry sand paper, which allowed me to achieve a near polished mirror finish. This portion of the exhaust system can be partially seen while fixed to the car, and driving about, so I decided this polished finish would look rather sharp, and to keep it looking good and prevent me from having to re-do this process each season, I coated it many times with high-temperature clear coat.
Clear coated polished Axle-back section
De-cat before wire brush
De-cat after wire brush
Now I needed to address the same issue with the remaining exhaust components. Given the time it took to bring the axle-back section to a shine, I decided it wouldn't be worth the time required to do the same for the de-cat and catalytic to rear axle section, that section is only ever seen when the car is lifted up anyways. But I couldn't just leave it in such a horrible condition, so I decided on a different approach. Again, I started with the wire brush wheel, first on the de-cat pipe, I was able to get it looking decent in no time at all, and I was beginning to appreciate the quality of these components again.
Then I moved onto the section between the catalytic and the rear axle, this had the most surface area requiring attention, and therefore took the most time to clean up. After hours with the wire brush wheel, I began preparations for the special paint these parts were to be covered in. POR-20 High Temperature Aluminum paint, this stuff is quite expensive, but has been proven time and time again to withstand extended durations exposed to temperatures up to 1400 degrees Fahrenheit, I knew this stuff would be perfect for what I wanted.


Cat-back after wire brush
Cat-back before wire brush
There is a very specific procedure that must be followed when working with this paint, and it isn't the easiest paint to work with either, but the results are astonishing and well worth the effort. The metal must all be prepared with their Metal Ready solution, which is effectively a spray bottle with phosphoric acid. I sprayed the solution over the entire surface and allowed it to soak for half an hour, it causes the metal to corrode and form a white chalky substance on the surface. Next I rinsed off any excess acid which water, and allowed the parts to air dry for 2 days. This paint is so delicate to work with that if you even get one drop of water, or sweat in the paint, the entire can must be thrown out! Following the instructions for each specific paint product can be strenuous, but it's the only way to make sure it turns out well. So make sure the surfaces are truly dry before beginning to paint. It's a very clever type of paint, once applied to the surface, it forms a chemical bond to the metal using the phosphoric chalky substance as a catalyst, and once dry, is so hard and tough that the paint cannot be scratched off, and will never, ever flake or chip. It's that good. The photo below is after 2 coats, the parts are hanging up to dry.
POR-20 hanging up to dry
Between the turbos and the catalytic...
Some of the most important exhaust components are within the first few feet of the turbos, in particular the first 12 inches or so, where the turbo dump pipes reside. The standard R32 items are really quite restrictive for the internally waste-gated design, and causes a lot of turbulence, a common upgrade is to install the R34 GTR dump pipes, as they are much more open and allow more exhaust to flow through quickly. The best design to handle the internal waste gate system, is to have a separate pipe which rejoins the exhaust stream further down the line, this results in the quickest turbo response, and the least amount of turbulent airflow, and we all know that the faster the turbos come on with the power, the quicker we'll be off mark.
RS*R Stainless Divided turbo dump pipes
Immediately after the dump pipes, comes the front-pipe/down-pipe, This part is key in setting up a well flowing exhaust system, the standard down-pipe is only 2" and really quite restrictive, so to free up some extra response and power, most people will move to an after-market down pipe, usually with 3" inlets, and a 3.5" outlet into the catalytic. There's two separate schools of though on this piece, the discussion is always about equal length runners versus smoother merge design with non-equal length runners.


RS*R down-pipe
Greddy MX Equal length down-pipe
It is said the advantage with equal length runners is that each turbos' exhaust gases will have equal lengths of pipe to cover, and will therefore help to prevent the dreaded turbo shuffling, where as a non-equal length kit takes the stance that it's not at all advantageous to have equal length because the peaks and valleys of the exhaust gas waves line up and create constructive interference. It's this wave theory that actually makes the equal-length pipe give your exhaust system much more of a grunt in the tone and is usually a little louder. Where as the non-equal length set up focuses on getting the gases out the end as quick as possible, and has the peaks and valleys align to give destructive interference which means that the exhaust gas will be moving quicker, this design also allows for a much smoother merging point. I had the choice to make as I had obtained one version of each design, at first I was using the Greddy MX Equal Length down pipe, but I opted for the RS*R down-pipe as it was paired with my new RS*R dump pipes. I also wanted a quieter exhaust noise to help void unnecessary police attention, and I generally felt the design was better in the RS*R items, plus they are a lot rarer than the Greddy kit. Below are two photos of the different pipes side by side:
RS*R & Greddy side by side


Equal length Vs straight design

Comments

  1. I'll surely put it up in mind the next I have a check on my exhaust. Great article.

    ReplyDelete
  2. Great article. never knew about the differences.

    ReplyDelete

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