Valves- carboning up

[2manytoys]

So why doesn't power get impacted if you get a 10% or greater restriction within all the valves (at the top end I mean). 10% would be generous too, as I've seen some that look 40% smaller (but may just be an optical illusion because of the state of them??)

[HYFR]

Arthur, did it again, same stretch of road I did the 8.0

I got a 8.2, just over half a tank of petrol this time, 8degree C

So, so far I've got

7.9
8.0
8.2

[PetrolDave]

So why doesn't power get impacted if you get a 10% or greater restriction within all the valves (at the top end I mean). 10% would be generous too, as I've seen some that look 40% smaller (but may just be an optical illusion because of the state of them??)

Because the air flow through the throttle bodies is smooth and uses all the available cross sectional area, but the air flow past the valves is turbulent and does not use all the available area - so carbon build up in the places where air flow is minimal or low has no or very small effect on the amount of air entering the engine.

[ArthurPE]

Because the air flow through the throttle bodies is smooth and uses all the available cross sectional area, but the air flow past the valves is turbulent and does not use all the available area - so carbon build up in the places where air flow is minimal or low has no or very small effect on the amount of air entering the engine.

yepper...

I may add that the TB sees 16 times the air a valve sees...
yet it's area is not 1/16th

TB ~ 6362 mm^2
valve ~ Pi x 26 (OD) x 20 (lift) ~ 1633 mm^2, so even if you derate it for deposits and the stem (hardly any impact due to the shape/gradient of the flow) to say 75% or 1200 mm^2, it still is 1/5th the area, but handles only 1/16 the the volume, that means the vel will be ~1/3 as much, and since DP ~ V^2 the pressure drop will only be 1/10th as much...hence the valve having negligiable impact...

[P_G]

An associated question for those of you who have had your valves and manifolds cleaned, what do you use to clean them? I hear the name Seafoam in the US but what about the UK. And would it not damage the coating on the engine components?

[2manytoys]

Carbie Cleaner, soap and water, with a cloth dremel was what we used.

Believe it or not, I've had mine cleaned again (by Audi this time). They suspect the PCV, and this has now been replaced. They will remove the manifold again in another 2000kms to check again.

This is doing my head in. I understand what people are saying, I really do, and I can see the theory behind it, but all I can say, is when it's cleaned it's better. It's significant. A 2nd gear pull, wait untill about 5500 and bam, the "boost" is back.

I think Audi really need to sit in a customers car that doesn't have the boost, and ONLY clean the valves, and then get back in it (ideally on the same day). It's so easy to feel. Maybe there is something else going on with the air when there is carbon there, I don't know.

[ArthurPE]

An associated question for those of you who have had your valves and manifolds cleaned, what do you use to clean them? I hear the name Seafoam in the US but what about the UK. And would it not damage the coating on the engine components?

if I were to clean mine (I think most can guess that ain't happening, lol)
I would not use any abrasive or force...
I would saturate rags with a solvent (Seafoam would be fine), pack them into the ports, and let it sit over night, keeping everything wet...

that should soften everything up enough to where some could be wiped off with the rags nd the rest could be scraped off with a plastic spatula...if not, let it sit some more, keep wetting the rags...

I don't think there is any effective way to do it without removing the manifold, then again, I don't think there is a need to do so to begin with

[HYFR]

... but all I can say, is when it's cleaned it's better. It's significant. A 2nd gear pull, wait untill about 5500 and bam, the "boost" is back.

but I have the "boost" after 5500rpm

and I have 70k on the clock and presumably very coked up valves if you believe the hype

[scaghead]

An associated question for those of you who have had your valves and manifolds cleaned, what do you use to clean them? I hear the name Seafoam in the US but what about the UK. And would it not damage the coating on the engine components?

sounds like you are thinking of giving it a go fella???

[P_G]

It will be the last result if my EPC light issue is not actually faulty sensor related but is becasue the runners are sticky due to carbon build up. Just waiting on advice.

[2manytoys]

... but all I can say, is when it's cleaned it's better. It's significant. A 2nd gear pull, wait untill about 5500 and bam, the "boost" is back.

but I have the "boost" after 5500rpm

and I have 70k on the clock and presumably very coked up valves if you believe the hype

Wow, by 70k my valves would be closed shut with carbon (based on the amount there by 30,000km).

How do you use your car? Do you do much expressway driving, track days or city?

Do you use Audi Oil (Castrol LLP 3) and V-Power fuel?

[HYFR]

Wow, by 70k my valves would be closed shut with carbon (based on the amount there by 30,000km).

How do you use your car? Do you do much expressway driving, track days or city?

Do you use Audi Oil (Castrol LLP 3) and V-Power fuel?

I do mainly motorway (as you can imagine), but when I get a chance i.e. country road, I use the full rev band....car doesnt really do many short stop start journeys

I ONLY use 99RON fuel, I think the ONLY time I put in 95 was when I bought the car from Audi it didnt have any fuel in and they gave me a £25 fuel voucher for a specific garage which didnt sell Super

[ArthurPE]

... but all I can say, is when it's cleaned it's better. It's significant. A 2nd gear pull, wait untill about 5500 and bam, the "boost" is back.

but I have the "boost" after 5500rpm

and I have 70k on the clock and presumably very coked up valves if you believe the hype

Wow, by 70k my valves would be closed shut with carbon (based on the amount there by 30,000km).

How do you use your car? Do you do much expressway driving, track days or city?

Do you use Audi Oil (Castrol LLP 3) and V-Power fuel?

probably not, they are self limiting, ie, velocity increases enough (due to constriction, less area) to scour the valves and remove new deposits before they can form/harden...

it also appears they grow in a nonlinear fashion, very rapidly at first then taper off...I'm guessing 90% in the first 10k miles, very little after that

[Sims]

I do mainly motorway (as you can imagine), but when I get a chance i.e. country road, I use the full rev band....car doesnt really do many short stop start journeys

I ONLY use 99RON fuel...

Your car should be the best performing B7 RS4 at the RR tomorrow.

Hope it goes well.

[ArthurPE]

ref rolling road
get all the set-up data, especially ramp time, operating mode, etc.
ask them to do a steady state run, hold the car at 7800 for 10+ sec
get raw, uncorrected, WHEEL data, NO correction factors
estimated crank numbers are useless...
get all correction factors if they insist on crank estimates
at least get both numbers/graphs, wheel & est. crank

anything less and your tossing $$$ away

I do mainly motorway (as you can imagine), but when I get a chance i.e. country road, I use the full rev band....car doesnt really do many short stop start journeys

I ONLY use 99RON fuel, I think the ONLY time I put in 95 was when I bought the car from Audi it didnt have any fuel in and they gave me a £25 fuel voucher for a specific garage which didnt sell Super