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Road to stage 2 - C43 2020

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Old Mar 25, 2026 | 05:57 AM
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2020 AMG C 43
Road to stage 2 - C43 2020

Hey All. This winter I've been busy getting my car maintained and upgraded. Wanted to share my experience as a DIY

The Plan
  • CTS Intercooler upgrade
  • Main and Low temp coolant drain + fill
  • Radiator clean/vacuum
  • Transmission w/ torque converter drain
  • CTS high flow cats
  • Stage 2 tune

There is no DIY instructions with this product. I contacted support and asked for any instructions (even basic ones) and only got a "needs to be installed by a professional mechanic". It's a shame because Wagner has instructions. So I just referenced that.
  • Take out the upper reinforcement or follow guides on radiator fan removal
  • Drain both main and low temp coolant. There is a drain plug on one side for one circuit. The other side has a hose you need to pull.

  • I did mine the hard way. Undid the charge pipes and intercooler with the upper reinforcement and fan still installed. Save yourself the hassle and remove those first. Undoing the very first bolts on the charge pipes almost made me quit this project. They are very hard to get but with the right tools and patience, you'll get them out.

  • The realization of how much room I have now. Also realized how much gunk was in the radiator fins. I had to go deeper and undo the radiator from the housing and at the very least vacuum it out.
  • At this point, I have access to the crank bolt. I had a friend rotate the engine slowly until I can see the torque converter drain bolt. Stick a zip tie into the drain hole and wait an hour for it to drain. Then drained from the pan. I got out about 7.5L of trans fluid. Mount the new pan in. Torque it down.

  • Now that everything was cleaned up I started the fitment on the CTS Intercooler. Few things to note.
    1. The upper silicon hose that mounts up to the throttle body was to long and couldn't mount the cooler into the bottom bracket. I took a razor blade to the hose and clipped off about a quarter of an inch.
    2. Make sure that when you mount it to the bottom bracket that both right and left mounting holes are inserted or else it wont fit right when you mount the radiator fan back.
    3. Sil-Glyde Silicon lube is your friend. Use a very tiny amount on all O-Rings and Silicon hoses. You will need it to mount/fit everything back in.
    4. The left cooler inlet is 1/16th of an inch to long. The radiator connection would not snap in. I had to sit there and file it down for 20 minutes until I got it to snap/click in.
    5. The provided clamps are good quality. I used them on the left side. On the right side, I used some lower profile ones as things were very tight
    6. For the outlet cooler connection to the oil cooler connection, you will need to cut the 90 degree cooler connection from the stock hose and mount it to the provided silicon hose.








  • Everything is mounted and fitted. Time to fill the coolant back on both circuits.



  • Filling the trans with my makeshift home depot pump. I pumped in 8.5L and used AUTEL scanner to bleed the valves and perform the oil level check.


Stay tuned for CTS cats install and custom stage 2 tune. I'll update the thread. Hit me up with any questions and I'll try to answer them. Cheers!

Last edited by atomek; Mar 25, 2026 at 06:11 AM.
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Old Mar 25, 2026 | 11:52 AM
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I took it for a test drive today and I didn't really feel any difference in performance. I'm currently on a stage 1 tune w/ Intake + Intercooler now. I'm assuming that once I get the high-flow cats installed and the stage 2 tune, I should feel a difference. SOON!
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Old Mar 27, 2026 | 07:59 PM
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Got the cats in... Not that bad of a job. Had to get another 3/8th extension to reach the bolts from the back of the turbos.

-Spray all the bolts with a nut buster spray and let it sit for 10-15 min. Do the o2 sensors as well.
-Undid the air box so you can get to the 2 plugs on each side.

-Undo the bolts from behind the turbo exhaust.

-Loosen the bolts from the back just to give you some play

-undo the bolts for the bracket and the clamp. The clamp you will need to pry/wiggle the cat to get it off.


They give you new rings that fit into the side where you clamp it down.


There is no clamp/rings to the back of the turbo. Just bolt it up
The 4 bolts and nuts they give you is for the bracket. you will need to transfer that over to the new cat.
Transfer the 02 sensors to new cat. Wire brush the threads. Add a small amount of anti seize, Torque it down to 50nm.
Wire brush your clamp and all of your bolts. Add a small bit of anti seize to the bolts.
Install in reverse order

Clamp torque is 19nm
All the other bolts are 22nm
Don't worry about the first start grey/white smoke... Its burn off from the new cats.
CEL light will come on in 5-10 miles. You will need to get stage 2 tune.

I called my tuner and gave him all my new mods and he's building the file. We'll see the gainz. My previous stage 1 tune was at 391hp at the wheels (did a dyno session last season).
What do y'all think I'll hit with these new mods and good stage 2 tune?
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Old Apr 18, 2026 | 07:44 AM
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Quick update.

So after a I sent my car to the tuner and got the stage 2 tune, I actually didn't feel any improvements. This had me 2nd guessing everything and also had me thinking that I'm at the limits and might need CPC/TCU unlock and tune.
After talking with my tuner, they took it for another day to log and troubleshoot.
Got call from them saying they found the issue... I had 3 boost leaks off the inter cooler clamps they found and resolved. They wanted me to do a few pulls before I left so that they can see the smile on my face. What a difference! Pulls hard, shifts great, and feels amazing.

Goes to show that DIY is rewarding but sometimes these little things make a huge difference. I could of sworn that it was tight but obviously not tight enough. I do remember myself going, yea that's tight enough
The tuner said his butt dyno thinks I'm pulling between 430 and 450 whp and one of his techs said its the fastest c43 he's been in (I know there's faster out there)
I have a Dyno session scheduled for June 6th to put some real numbers on paper. My Stage 1 was 391whp. Wish me luck! Cheers!
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