Drop in BHP due to Carbon Build up - Gen 2 997?

Drop in BHP due to Carbon Build up - Gen 2 997?

Author
Discussion

997c2scab

Original Poster:

422 posts

180 months

Wednesday 10th November 2010
quotequote all
Guys,

I am not technically minded so bare with me on this……. I have been doing some research today on behalf of a colleague regarding the reported reduction of BHP due to Carbon Build up on FSI engines of which are even more prominent in high performance engine such as the RS4. (Reported figures are from 420 BHP down to 330 BHP

With the above in mind and the Gen 2 997 and future cars being direct injection could this be a similar fault that will appear in years to with the Porsche or is it just a design fault of Audi engines?

SunDiver

780 posts

236 months

Wednesday 10th November 2010
quotequote all
I've pondered this too - keen to hear if it hits Porsche engines. For those that are interested, here's some pictures/comments on the issue for RS4s.

http://www.mrctuning.com/index.php?option=com_cont...

mayes911

5,188 posts

184 months

Wednesday 10th November 2010
quotequote all
me thinks this does affect the porsche like all dfi cars.although has the car had a lot of town use instead of motorway (needs an italian tune up every now and then).this is one of the reasons i avoided buying a new gen 2 car and bought a new gen1. we know the problems with the gen1 and the fixes.

Wills2

22,669 posts

174 months

Wednesday 10th November 2010
quotequote all

I've now done 33k in mine and I haven't noticed any drop off in performance infact it feels like its loosening up nicely... driving

betternotbigger

1,059 posts

174 months

Wednesday 10th November 2010
quotequote all
Plenty of scaremongering and idle speculation to be found on this topic elsewhere. Welcome to the internet.

And yet, not one single case of carbon-induced dfi-droop ever found in a 911.

VAG a different story, mind...

Edited by betternotbigger on Wednesday 10th November 20:24

bcnrml

2,107 posts

209 months

Wednesday 10th November 2010
quotequote all
Actually, if you dig up Ian_UK1's thread titled something like "heads up - carbon on porky engines", you'll see a decent, helpful and technically enlightening discussion with evidence of this matter.

After reviewing that, come back and demonstrate why it is internet hearsay.

As usual, some people dive in here feet first to defend Porsche engines before using their heads to check the facts - and the clear evidence on the web about the current patterns.

g7jhp

6,959 posts

237 months

Wednesday 10th November 2010
quotequote all
Drive it properly and use all the rev range and you'll burn off the carbon!

Wills2

22,669 posts

174 months

Wednesday 10th November 2010
quotequote all
bcnrml said:
Actually, if you dig up Ian_UK1's thread titled something like "heads up - carbon on porky engines", you'll see a decent, helpful and technically enlightening discussion with evidence of this matter.

After reviewing that, come back and demonstrate why it is internet hearsay.

As usual, some people dive in here feet first to defend Porsche engines before using their heads to check the facts - and the clear evidence on the web about the current patterns.
In the absence of any real facts relating to the gen2 911 engine you have to rely on real world experience.

After 33k miles my car it feels as strong as ever, it remains to be seen if they suffer from the same issues that plague other DFI engines.

I have no idea, but I wonder if the horizontal config of the engine means it will not be subject to the same issues of the vertically arranged DFI engines? i.e when the fuel is introduced into the cylinder does it behave differently and manage to wash the back of the valves? (I'm thinking out loud so no flaming if that's just utter nonsense)

Edited by Wills2 on Wednesday 10th November 21:23

Martian O

2,734 posts

161 months

Wednesday 10th November 2010
quotequote all
I had carbon build-up problems with a Mitsubishi DFI (GDI petrol) engine a few years back. The main dealer who remedied the fault under warranty told me it was a common problem with these engines and there was no alternative apart from regular (~20K miles) shot blasts with walnut shells in the cylinder head.

Porsche engines.....who knows, but we do know that they aren't as reliable as we've been lead to believe.

Wills2

22,669 posts

174 months

Wednesday 10th November 2010
quotequote all
Martian O said:
Porsche engines.....who knows, but we do know that they aren't as reliable as we've been lead to believe.
What issues have you had with yours?

Martian O

2,734 posts

161 months

Wednesday 10th November 2010
quotequote all
Wills2 said:
Martian O said:
Porsche engines.....who knows, but we do know that they aren't as reliable as we've been lead to believe.
What issues have you had with yours?
None, it's one of the reliable ones, a GT1 block 997.1 Turbo.

I popped into my independent on the way out this afternoon and they had a 996 3.4, 997 3.6 and two Boxster engines in for IMS/RMS/cracked liner repairs!

Just take a look at the sticky for wet-sump engines...............


Wills2

22,669 posts

174 months

Wednesday 10th November 2010
quotequote all
Martian O said:
Wills2 said:
Martian O said:
Porsche engines.....who knows, but we do know that they aren't as reliable as we've been lead to believe.
What issues have you had with yours?
None, it's one of the reliable ones, a GT1 block 997.1 Turbo.

I popped into my independent on the way out this afternoon and they had a 996 3.4, 997 3.6 and two Boxster engines in for IMS/RMS/cracked liner repairs!

Just take a look at the sticky for wet-sump engines...............
The gen2 engine was totally redesigned so that wouldn't be relevant....

Martian O

2,734 posts

161 months

Wednesday 10th November 2010
quotequote all
All I was stating is that previous Porsche engines generally haven't been as bomb-proof as we would've hoped or expected. Agreed, I think it's too early to write-off the DFI engine at the moment, but on basing it on previous Porsche designs, I am holding my breath regarding DFI cokeing issues.....

Edited by Martian O on Wednesday 10th November 22:46

Wills2

22,669 posts

174 months

Wednesday 10th November 2010
quotequote all
Martian O said:
All I was stating is that previous Porsche engines generally haven't been as bomb-proof as we would've hoped or expected. Agreed, I think it's too early to write-off the DFI engine at the moment, but on basing it on previous Porsche designs, I am holding my breath regarding DFI cokeing issues.....

Edited by Martian O on Wednesday 10th November 22:46
Why when you have a GT1 block? wink

Martian O

2,734 posts

161 months

Wednesday 10th November 2010
quotequote all
Wills2 said:
Martian O said:
All I was stating is that previous Porsche engines generally haven't been as bomb-proof as we would've hoped or expected. Agreed, I think it's too early to write-off the DFI engine at the moment, but on basing it on previous Porsche designs, I am holding my breath regarding DFI cokeing issues.....

Edited by Martian O on Wednesday 10th November 22:46
Why when you have a GT1 block? wink
For when/if I consider a 997.2 Turbo!

Wills2

22,669 posts

174 months

Wednesday 10th November 2010
quotequote all
Martian O said:
Wills2 said:
Martian O said:
All I was stating is that previous Porsche engines generally haven't been as bomb-proof as we would've hoped or expected. Agreed, I think it's too early to write-off the DFI engine at the moment, but on basing it on previous Porsche designs, I am holding my breath regarding DFI cokeing issues.....

Edited by Martian O on Wednesday 10th November 22:46
Why when you have a GT1 block? wink
For when/if I consider a 997.2 Turbo!
I wouldn't mate I hear they suffer from coking and have porous liners. biggrin

sbirty

98 posts

161 months

Thursday 11th November 2010
quotequote all
Might be worthwhile asking for a dyno report before buying a used gen2 with more than 20k

lynchygt3

633 posts

182 months

Thursday 11th November 2010
quotequote all
but most foke on here thinks a dyno report is of no any use to anyone ! as they say they are all wrong ! so thats that idea out the window

bcnrml

2,107 posts

209 months

Thursday 11th November 2010
quotequote all
Martian O said:
Wills2 said:
Martian O said:
All I was stating is that previous Porsche engines generally haven't been as bomb-proof as we would've hoped or expected. Agreed, I think it's too early to write-off the DFI engine at the moment, but on basing it on previous Porsche designs, I am holding my breath regarding DFI cokeing issues.....

Edited by Martian O on Wednesday 10th November 22:46
Why when you have a GT1 block? wink
For when/if I consider a 997.2 Turbo!
thumbup

Sounds like someone doing his/her research without blinkers or rose tinted specs on.

The point of a test before buying a used one is spot on - and a dyno alone wouldn't be enough. I say get a camera down there as some of the independents on here recommend.

Remarkable isn't it, that porker engines should now come with the results of biopsies to give owners better peace of mind than the wonderful 111 point check? smile

Ian_UK1

1,514 posts

193 months

Thursday 11th November 2010
quotequote all
g7jhp said:
Drive it properly and use all the rev range and you'll burn off the carbon!
Unfortunately not. The carbon build-up on the back of the inlet valves can't be burned-off as it isn't inside the combustion chamber, nor is it washed-off by incoming fuel (as is the case with port-fuel-injection engines) as the fuel is injected straight into the combustion chamber.

The carbon build-up is due to 2 things: oil vapour from the crank case re-breather that enters the inlet manifold and oil seepage from the valve guides. In standard fuel-injection engines, where fuel is injected into the inlet port, oil from these sources that hits the back of the inlet valves is washed away on every inlet stroke of that cylinder. The fuel passing over the inlet valve also cools it due to evaporation. In a DFI engine, the oil isn't washed away as no fuel goes past the valve and the inlet valves also run a lot hotter as there is no cooling effect from the incoming fuel. This has the effect of making any oil/oil vapour carbonise on the back of the (much hotter) inlet valve and the result is the build-up seen in many photographs.

The more effective the oil separation process in the re-breather circuit, the less oil vapour will be present in the inlet tracts, but this oil separation is not that efficient in practice.

The latest thinking to deal with this problem (that is not yet, to my knowledge, implemented in any current engines) is to coat the inlet ports and valve backs with a catalyst that will prevent the carbon from forming.

There will inevitably be some carbon build-up on the DFI engines and the only real solution will unfortunately be an expensive and thorough, old-fashioned de-coke! How quickly the build-up will happen and to what extent it will impact on power/torque outputs over time, nobody seems to have addressed yet. Unfortunately there are too many people in denial that the problem (if that's the right thing to call it - it's just an inevitable consequence of the engine type in reality) even exists.

My 7S.2 has about 8500 miles on it now. I'd be happy to have someone examine/photograph the state of its inlet valves with a suitable optical probe if any engineering shop can do so/would like to do so? We can then publish the pics on here to get a proper idea as to how quickly these deposits begin to build-up.

Ian