RS5 carbon clean DIY

A5/S5/RS5
#41

Can’t sleep. So I had a hunch based on how Audi likes to share parts across various models…4.2L/8=.525 Take .525x10 and what do you get? 5.25 of course! As in liters. As in displacement of Audi’s V10. So…cross referencing the part number for the RS5 piston (079107066CS) shows that it’s the same part for the Audi R8 V10. At first I thought it was just the 2010-2012 models but I’m looking at 2014 and 2015 now and it even mentions it’s the same piston for the RS5. The V10 and V10+ pistons are identical.

So this is good news. Not only will the OEM piston the same but so is the ring package. Additionally, anyone making pistons for the R8 (like JE), well their pistons should work just fine for the RS5 too.

#42

The pistons should be the same as they are all the same bore size

Bore 84.5 4.2 FSI 8500 RS5… RS4…S8. R8 R8 V10 V10+
Stroke 92.8

All of those and more have the 84.5 bore and stroke. And all of those use the same piston dimensions.

But the supercharged 3.0T also has the same bore. Its a different stroke.

[quote]Keep in mind its not the piston thats different its the ring packs on the piston.
[/quote]
I mentioned that the pistons are not different its the ring packs and end gaps that are different. That is the entire issue.

#43

Even the ring packs are the same part number. Literally, between the RS5 and the R8V10 up to 2017, the piston, ring pack, rods and bearings all have the same part number. All are forged.

Now the RS4 is a completely different animal. Yes, it’s the same bore but the piston, rod, everything, is different.

From what I’ve been reading, what it really comes down to is how healthy is the engine (ring package) prior to installing a supercharger which is kind of a “well, yeah duh” moment. But if the car is still sealing fine…

After reading through a ton of stuff, it seems, for the R8, that it’s about a 65ft. pound per cylinder “safe” limit on a healthy engine. That’s about 520 ft. pounds which is, conversely, what TVS Engineering out of the Netherlands said their TCU tune would support on the DL501. Hp wise, we’re looking at 80hp/cylinder (wheel) which would put the RS5 at 640 wheel hp. 800 seems to be the manageable limit on the R8 with a supercharger like the Eaton TVS R2300, more with a turbo it. But at the mid 800 level, everyone switches away from the Bosch Monotonic MED. I think the RS5 has the 17.1 if I remember correctly and not sure what the later OBD port flushable R8’s (2013+) run. They all go to a syvecs ECU which is more powerful than the MED and more “tunable” including boost management in lower gears.

The cranks are forged with a split pin and special heat treating. The R8’s crank is going to be somewhat weaker than the RS5 as it’s longer. The R8 V10 also has a nodular iron counterbalance where the RS5 has none.

The bottom line, IMO, is the RS5 with a properly sized blower, intercooler and fuel system should run 550 wheel hp easily and reliably on the OEM bottom end. A freshly carbon-cleaned one anyway, LOL.

The one thing that’s still somewhat of a mystery is the Alusil liners. I’m assuming the V10+ and the RS5 CFSA block both use the same type of cylinder coating. If you wanted to run aftermarket pistons/ring package, I’m assuming you can’t just plop the new stuff in there without re-honing or retreating the bores (for lack of a better description). I need to reach out to more people on that one.

I’ve been looking and looking for a photo of the OEM piston and haven’t found a ton for the CFSA engine but did find a few. I can’t really tell much just from the photos and companies like JE aren’t listing exactly what makes their piston an improved design over OEM in this specific application.

But here are two photos I did find.

https://i.postimg.cc/g0p4CfXT/s-l1600-3.jpg


https://i.postimg.cc/wvzfN2Cn/s-l1600-2.jpg

Here’s a B7 RS4 piston/rod

https://i.postimg.cc/fbc5MXVC/RS4-B7-piston.jpg


https://i.postimg.cc/VNQDy4k5/RS4-B7-piston-2.jpg

#44

Ok…part one of the carbon cleaning video is done! Working on editing part two now.
https://youtu.be/zlLmz4pmlSU

#45

Part two is now up as well.
https://youtu.be/uQnOu0W4GGQ

#46

I thought I’d update this thread as I have some new, interesting information. I had an injector failure and decided to replace all eight injectors. This happened approximately 10,000 miles after my carbon clean. Since I had to pull the upper and lower intake manifolds, it’d be a great time to check out how much carbon is built-up over the course of a year/10K miles.

It wasn’t horrible, but it’s definitely rearing it’s ugly head again. I’m convinced it’s getting past the valve guides/stem seals and dripping down the valve stem in addition to what’s being injected into the intake charge via the PCV.

I’m going to do a little experiment in the next few days, I’ll be running some CRC valve cleaner into the engine per their instructions to see if it makes any noticeable difference visually. I have some new intake manifold seals coming in and I’ll recheck the valves in a week to see if it did indeed remove a good amount of the gunk buildup.

All of the carbon buildup was soft and gooey. It hadn’t hardened significantly yet so the valve cleaner may have a fighting chance. If it does work, it might be something one does every oil change (every 5,000 miles) as a very inexpensive way to prolong the need for a carbon cleaning with walnut shells or similar.

The port dividers also had a thin layer of gunk on them. I pulled all of those and cleaned them off. Intake flaps had gunk as well.

#47

Interesting to see the carbon building back up. Try pulling the port dividers. There is a little performance there especially if you have the JHM tune and all the dividers end up doing is being a carbon build up plate.

Injector failure seems to be a REALLY big issue with the FSI motors. WAY more than people know. carbon is a big part of it. Great update

#48

I may do that when I’m “back in there” next weekend. I did the CRC valve clean today and I was a bit shocked, the idle was definitely a hair smoother (it was already good) and I ran my best time to date despite the poor DA and mid-70’s temps. I think I would have been sub 12 seconds had it been 10-15 degrees cooler with a better DA. I never seem to get conditions where the DA isn’t at least 2100ft. and usually it’s 3000+. But what can you do…

#49

I would love to see the results and hear more about your experience with the CRC

#50

I’ll be checking the valves either tomorrow or on Monday and will have an update then. Car is idling like a Rolls Royce but most of this is probably due to the brand new injectors.