Valves- carboning up

[Gumball0r]

Thanks.
Yes it will be back indeed and I'm actually sharing your opinion on carbon vs power. The thing is, I'm very tempted to talk to my dealer about wether or not the carbon is a warranty issue.

[ArthurPE]

Thanks.
Yes it will be back indeed and I'm actually sharing your opinion on carbon vs power. The thing is, I'm very tempted to talk to my dealer about wether or not the carbon is a warranty issue.

take it in to him, with pics from the forum, tell him there is a lot of 'chatter' going on concerning this issue in the Audi forums, ask him what he thinks you should do...ask him:
affect power?
longevity?
fuel economy?

[ArthurPE]

it would not make sense to retool for a new engine, for such a limited production model, especially when you still have the R8 engine currently in production, that already has 2 intake tracts...I would expect to see the base R8 re-rated and modded (higher rev) to match the RS5 rating...


http://auditalk.org/
The 2011 RS5 from Audi will be uncovered during the Geneva Motor Show this March, and it will have an upgraded powerplant from the RS4 under its hood.

http://www.carmagazine.co.uk/News/Searc ... S5-cabrio/
We’re told it’s the same high-revving engine that powered the outgoing RS4, albeit spruced up with the latest Ingolstadt know-how

[SR71]

the accuracy of VagCom airflow measurment is at best 6%, so a 2% difference is meaningless, lost in the noise...
I know a lot about airflow measurement...and an inline, full section, multi-pitot, averaging sensor with airflow straighteners with a 0.1% transmitter can't do much better than 3% overall...add in temperature, atm P and humidity compensation, and the AFM and VagCom MIGHT be able to do +/-8%, maybe...doubt it though
so how can a 2% difference mean anything?

So you are suggesting the MAF on the B7 reads to only 6% accuracy?

Is Audi aware of your opinions on their airflow measurement?

but the accuracy doesn't matter, becasue it's only 1 variable in the fuel rate equation: throttle position, calculated load, rpm, temp, O2 sensors, etc....it's a rough approximation, trimmed (in control parlence, reset) by many other variables...

Which is why one uses VAGCOM as a tool because it measures all these things like throttle position, rpm, altitude compensation etc etc

No guessing involved.

Pseudo-scientific tests where owners submit results based on "no incline, half a tank of fuel, bit of a cross-wind" are not, I contend, able to confirm the hypothesis I am interested in.

Maybe they are sufficient for your purposes.

Anyone who plugs VAGCOM into their diagnostic port will see a difference in airflow pre and post cleaning. Even more so if you port the manifold at the same time.

Proved many times.

Similarly, the performance of the car is thus affected for obvious reasons. Whether that margin is significant depends on what you deem the word significant to mean.

[2manytoys]

I also find it interesting that the discussion around the RS5 is more air allows it the make more power up top. I bet carboned (excessive) buildup takes the power away at the top too.

As some claim, if air flow restriction isn't going to impact power, why bother with dual throttle bodies. I suspect the RS4 engine needs all the air it can get above 6000rpm to make the 420hp!

[P_G]

The design of the RS5 allows it to and two 70mm bodies is better than one 90mm body? The RS5 engine bay and layout is far less compact than that of the RS4 and perhaps it was the amount of air available to the RS4 engine that determined they only needed a 90mm throttle body. Now the RS5 has more capacity for airflow into the engine two throttle bodies are needed. Who nows...except Audi engineers of course.

And are you talking about air flow restriction in terms of actual air available to pass through the engine or restriction in terms of carbon build up More air flow through an engine surely would always be a good idea and perhaps all carbonisation may do is build up pressure in the airflow that would mean the same amount of air flows into the cylinders compared to that of a clean manifold?

[caldy]

heck no, remove manifold, clean away
removal & reinstall might be 2-3 hours total...less if practiced
cleaning takes a while, maybe 8 hours+

Arthur - you'd need to be very well practised to remove and replace an inlet manifold in less than 3 hours. It's the fiddly bits that take the time. You need a child's fingers with the strength of an adult's to handle all the clips and hoses. Heaven forbid if you drop something during the rebuild......thank God for magnetic probes!

[ArthurPE]

6% is generous, probably less
as a pilot you know the only way to meaure flow is with a pitot, this is a hot wire anemometer...we bought lab grade instruments for containmemt & clean rooms that got 8-10% at best, that is when calibrated and located properly, no elbows, constrictions, 10 OD upstream, 5 OD downstream...

but if it is that accurate and can hold stoich ratio within 0.06 point, without the trimming of the other variables isn't that sufficient?

I'll take a real-worl, time test, any day over a dyno...
that is why 1/4 mile > dyno for anyone who does this for a living...
that is why mags time cars, and do not repeort dyno results or airflow mass readings, lol

I guess we'll have to agree to disagree

So you are suggesting the MAF on the B7 reads to only 6% accuracy?
Is Audi aware of your opinions on their airflow measurement?

Which is why one uses VAGCOM as a tool because it measures all these things like throttle position, rpm, altitude compensation etc etc

No guessing involved.
Pseudo-scientific tests where owners submit results based on "no incline, half a tank of fuel, bit of a cross-wind" are not, I contend, able to confirm the hypothesis I am interested in.

Maybe they are sufficient for your purposes.

Anyone who plugs VAGCOM into their diagnostic port will see a difference in airflow pre and post cleaning. Even more so if you port the manifold at the same time.

Proved many times.

Similarly, the performance of the car is thus affected for obvious reasons. Whether that margin is significant depends on what you deem the word significant to mean.

[ArthurPE]

I also find it interesting that the discussion around the RS5 is more air allows it the make more power up top. I bet carboned (excessive) buildup takes the power away at the top too.

As some claim, if air flow restriction isn't going to impact power, why bother with dual throttle bodies. I suspect the RS4 engine needs all the air it can get above 6000rpm to make the 420hp!

carbon...a couple of % decrease, MAYBE, if any...
2 TB's a 100% increase
see the difference? and why one would impact and the other wouldn't?
order of magnitude of difference 50 times
as I said before, the TB's are the limiting factor, NOT the valave inlet area...so occlusion there will have little, if any, impact, IMO

they do this to rev the engine high, 'pump' more air, the engine rev'ing higher makes the power, not more air per se, but you need the air when you rev higher...chicken and egg thing...

[SR71]

At a given rpm, for a given engine, whether or not you can increase power will depend on what you can do volumetric efficiency.

If you can raise it 7%, you'll get 7% more power.

Likewise, if you can supply more air to make it sensible to rev to 7% higher, you'll get 7% more power.

The problem with the RS4 is that beyond 7800rpm, the mass flow rate through the engine starts to reduce with the commensurate effects on power. No point except, like Arthur says, for top speed.

The RS5 solution is dual 70mm TB's which are not restrictive at >7800rpm.

Having established that at 7800rpm the RS4 inlet is "maxed out", it seems self-evident to me that if you place further restrictions in the inlet....

Likewise, though, it seems quite plausible to me, that fitting dual 70mm TB's to a RS4 would make absolute sense if you wanted to rev your motor to 8300+rpm because it would quite happily breath the requisite amount of air to make additional power....all other things being equal.

I'd be first in line for a dual 70mm TB retrofit if it ever became an option.

Like you say though, its hard to see how it could ever fit in.

Some wizardry taking place there!

[Sims]

Some more stuff here about the RS5, and it's engine etc

http://www.fourtitude.com/news/publish/ ... 5818.shtml

[sonny]

Interesting.

[PetrolDave]

The design of the RS5 allows it to and two 70mm bodies is better than one 90mm body?

Think about the cross sectional are of 2 70mm diameter bodies versus one 90mm...

2 x 70mm diameter = 30,787 sq mm

1 x 90mm diameter = 25,447 sq mm

So the RS5 throttle bodies have 20% more area than the RS4 throttle body, which means more air can get into the engine.

[ArthurPE]

so the velocity is 20% less (Q = V x A)
and so if the velocity in the 70's is 80% (0.80 times as much) as that in the single 90
the pressure drop will by only ~64% as much (DP ~ (V70/V90)^2 ~ 0.8^2)
a lot less...which will reduce pumping losses a bit, increase vol eff, and gain a few ponies...primarily the difference between:
8300/7800 x 420 ~ 447 HP and the 450 rating, ~ 3 HP

Dave don't know how you did it, your % is correct, but wouldn't the areas be?: (edit, you used the Diam. vs radius)
70's: 2 x Pi x (70/2)^2 ~ 7697 mm^2
90: 1 x Pi x (90/2)^2 ~ 6362
mm^2
6362/7697 ~ 0.82 or 7697/6362 ~ 1.2 or +20% larger...

[P_G]

The design of the RS5 allows it to and two 70mm bodies is better than one 90mm body?

Think about the cross sectional are of 2 70mm diameter bodies versus one 90mm...

2 x 70mm diameter = 30,787 sq mm

1 x 90mm diameter = 25,447 sq mm

So the RS5 throttle bodies have 20% more area than the RS4 throttle body, which means more air can get into the engine.

That's what I was trying to suggest. It has long been documented that the limitation to the RS4 power has been irflow so 2x 70 mm to take full advantage of the twin air intakes makes sense. The air intake in the RS4 I suspect would not warrant this configuration and I'm not sure if there would be space for them either whereas the size of the A/S/RS5 chassis would.