"Carbon build-up"

[Qisha]

Dear Friends,

as promised, i would like to say a word or two concerning „Carbon build-up“:

What is “Carbon build-up” and how does it come into being:

With fuel direct injection the cylinder heads and valves are no longer “washed” by fuel, which leads to a lacking “cleaning factor”. This is where the exhaust gas recirculation combined with the ventilation vapor of the crankcase ventilation and oil starts to build up. Particles of dirt and jets of water coming through the air intake path form into firmly adhering layer. This layer is taken up within the chambers of the cylinder heads and the admission valves, resulting in a rough surface, the airflow cross-sections become more narrow leading to non optimal air interlacing and cylinder charge. In total the results of “Carbon build-up” can be bad exhaust emissions, lower power output and higher consumption. In worst case the “Carbon build-up” affects the valve train. The valves can not close completely, which leads to low compression on the relevant cylinder, the fuel composition is not “fired”.

Factors that promote “Carbon build-up”:

Low quality fuel

Frequent short range driving

Preventing higher engine temps

Low RPM driving

intermittent driving

long time „not-using“

using non-specific engine oil


Audi RS 5 and „Carbon build-up“, do i have to worry?

As you might already know, the RS 5 engine ist based on the RS 4 V8 version. Main “Carbon build-up” relevant points that have been altered:

Engine production tolerance over again significant improved

Engine oil temp is increased by ~10°C

Modified piston rings


Resume:

The probability of „Carbon build-up“ within the RS 5 engine is nominal.

Qisha

PS: as the RS 4 V8 was also mentioned you migh like to note, that the engines from build date CW20/2007 received a altered cylinder head with different piston rings.

[Lmg]

Well, that's certainy interesting.

Thanks for the info, Qisha!

[artur777]

very interesting, Qisha
thanks a lot

[iconcls]

Rode like a rented mule by Audi regarding DRC in the RS 6, then having Audi claim it was fixed in the RS 4 but then only to see continued failures, I'm more than a bit skeptical. Audi has lost nearly all credibility with me so I honestly do not know what to make of their promises any longer.

[Sims]

Well, that's certainy interesting.

Thanks for the info, Qisha!

+1. Really appreciate your frank and upfront answer. So a car even with less than 20,000kms could have the dreaded carbon build up?

[MihokS5]

http://www.rs6.com/showthread.php/19...l=1#post185517

Thanks Qisha-my S5 is an 08 with about 12K on it-I'm thinking of doing a BG fuel induction cleaning as a preventitive maintenance-would you sugegst that? Thanks!

[Andyuk911]

...but, as much as what Qisha says, it will happen, this is fact. There is nothing you can do to stop this and over time performance will be impacted. Remember, this is nothing to do with Audi, all Direct Injection engines will suffer this, 997 Gen II, Ferrari California, 458 etc. Will I buy another FSI car, yep I will ...

Now back on topic .. seen the pixs of the RS5 on the Stand, butt ugly wheels to me !

[Qisha]

Thanks Qisha-my S5 is an 08 with about 12K on it-I'm thinking of doing a BG fuel induction cleaning as a preventitive maintenance-would you sugegst that? Thanks!

Dear MihokS5,

if you are driving your car more or less daily and not only short distance, you are using premium fuel, i dont see a need but it cant do any worse. Keep in mind that the pre-cats are close to the cylinders, overgreasing the combustion mix due to adding to much cleaning fluid can lead to a cat damage by overheating.

Qisha

[Sims]

Dear MihokS5,

if you are driving your car more or less daily and not only short distance, you are using premium fuel, i

Hi Q,

I am using premium fuel, correct oil, correct temperature, minimum 20kms run etc.

But I don't use the car daily - sometimes only twice a week.

Also because of the road conditions, I cannot drive at high revs unless I keep the car in 1 & 2nd gear.

How does this impact?

Surely if anyone buying an RS4 would have been told you can only use for long journeys, and everyday and at high revs, they may not buy the car?

Thanks

[Sims]

As you might already know, the RS 5 engine ist based on the RS 4 V8 version. Main “Carbon build-up” relevant points that have been altered:

Engine production tolerance over again significant improved

Engine oil temp is increased by ~10°C

Modified piston rings


Resume:

The probability of „Carbon build-up“ within the RS 5 engine is nominal.

Qisha

PS: as the RS 4 V8 was also mentioned you migh like to note, that the engines from build date CW20/2007 received a altered cylinder head with different piston rings.

Is it the same cylinder head & piston rings for the post CW20/2007 RS4's and the RS5?

Can you modify RS4's to run the 10C higher temperature, if that helps?

Production tolerance - were many RS4's low on power from production? What is the accepted tolerance? Are there amy cars that made more than the stated power?

You mention good quality fuel again and again - what is the minimum octane?

Cheers

[Lmg]

You mention good quality fuel again and again - what is the minimum octane?

My guess would be 98 octanes.

[Andyuk911]

PP, higher temp is actually worse as the oil breaks down ...

Trust me, bottom line you can't stop it, UNLESS you install NOS, which according to a chap I met at Brands Hatch using a TFSI Golf, the NOS use helps to keep the vanes and Valves cleanish.

Qisha, I think you posting some 'red herrings', please stop it unless you are able to supply valve/manifold pictures to prove what you say.

Most people in the know, accept FSI and the carbon and I am sure will just can clean when appropriate - UK folks can go to MRC

[Andyuk911]

PP,

Re fuel's, for UK running Super Unleaded, this has two benefits.

1. the ignition timing can be advanced, thus a bigger bang can be produced BEFORE the spark plug sets the fuel off in the cylinder.

2. Additional cleaning additives, which for a FSI engine ONLY help in the cylinder, NOWHERE else.

[Sims]

PP,

Re fuel's, for UK running Super Unleaded, this has two benefits.

1. the ignition timing can be advanced, thus a bigger bang can be produced BEFORE the spark plug sets the fuel off in the cylinder.

2. Additional cleaning additives, which for a FSI engine ONLY help in the cylinder, NOWHERE else.

Thanks for that. I have only used super unleaded but some claim some super's are better than others e.g Shell Optimax. And in the apparently the fuel octane claimed is often not what it says on the pump!!!

[Sims]

Trust me, bottom line you can't stop it, UNLESS you install NOS,

Most people in the know, accept FSI and the carbon and I am sure will just can clean when appropriate - UK folks can go to MRC

NOS? I am not technical.

Are most people in the know about it's impact? is this akin to an engine decoke?

[MihokS5]

Dear MihokS5,

if you are driving your car more or less daily and not only short distance, you are using premium fuel, i dont see a need but it cant do any worse. Keep in mind that the pre-cats are close to the cylinders, overgreasing the combustion mix due to adding to much cleaning fluid can lead to a cat damage by overheating.

Qisha

Q-
I'm trying to get my facts straight about carbon/oil consumption. I understand that "carbon" is a result of the combustion process and there is no way around it. But how does oil quality/temp/ affect how much carbon an engine produces if the main things going into the cylinder are air/fuel? Our the FSI engines burning oil due to the piston ring design? Or are they losing oil in the crankcase due to oil breaking down? Sorry for my lack of knowledge-just trying to understand

[Al Pettee]

Dear Friends,

as promised, i would like to say a word or two concerning „Carbon build-up“:

What is “Carbon build-up” and how does it come into being:

With fuel direct injection the cylinder heads and valves are no longer “washed” by fuel, which leads to a lacking “cleaning factor”. This is where the exhaust gas recirculation combined with the ventilation vapor of the crankcase ventilation and oil starts to build up. Particles of dirt and jets of water coming through the air intake path form into firmly adhering layer. This layer is taken up within the chambers of the cylinder heads and the admission valves, resulting in a rough surface, the airflow cross-sections become more narrow leading to non optimal air interlacing and cylinder charge. In total the results of “Carbon build-up” can be bad exhaust emissions, lower power output and higher consumption. In worst case the “Carbon build-up” affects the valve train. The valves can not close completely, which leads to low compression on the relevant cylinder, the fuel composition is not “fired”.

Factors that promote “Carbon build-up”:

Low quality fuel

Frequent short range driving

Preventing higher engine temps

Low RPM driving

intermittent driving

long time „not-using“

using non-specific engine oil


Audi RS 5 and „Carbon build-up“, do i have to worry?

As you might already know, the RS 5 engine ist based on the RS 4 V8 version. Main “Carbon build-up” relevant points that have been altered:

Engine production tolerance over again significant improved

Engine oil temp is increased by ~10°C

Modified piston rings


Resume:

The probability of „Carbon build-up“ within the RS 5 engine is nominal.

Qisha

PS: as the RS 4 V8 was also mentioned you migh like to note, that the engines from build date CW20/2007 received a altered cylinder head with different piston rings.

So I guess that means that by driving my supercharged RS4 on 100 octane fuel and constantly bouncing off the rev limiter, I am minimizing carbon build-up!

[Sims]

So I guess that means that by driving my supercharged RS4 on 100 octane fuel and constantly bouncing off the rev limiter, I am minimizing carbon build-up!

You also need to go on long journeys and everyday. And high revs only after engine is warmed up (so if takes a long time to warm up, there will be carbon buildup in the interim - best to keep the car in a warm garage with a sump heater)