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

[bcnrml]

Ian_UK1 said:

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

Ian, that's exemplary.

I am pleased that you joined this thread.

[Ian_UK1]

bcnrml said:

Ian, that's exemplary.

I am pleased that you joined this thread.

Thanks for the compliment. I think this issue does give people genuine cause for concern and if we can in some way begin to quantify its effects (or otherwise) in the real world, this can only be a good thing.

[nxi20]

This'll sort the problem

http://video.google.com/videoplay?docid=6187290865...

[Mermaid]

Ian_UK1 said:

I think this issue does give people genuine cause for concern and if we can in some way begin to quantify its effects (or otherwise) in the real world, this can only be a good thing.

Thanks, googled the issue and not any notable mentions of Porsche engines being affected or going pop, but picked this one for an Audi.

http://www.rs246.com/index.php?name=PNphpBB2&f...

[mayes911]

cayman/boxster 2.9 no ims and no dfi got to be best bet for longtevity now!!!!!

[Mermaid]

mayes911 said:

cayman/boxster 2.9 no ims and no dfi got to be best bet for longtevity now!!!!!

Also all GT2/GT3's surely.

[mayes911]

mermaid said "Also all GT2/GT3's surely" agreed (maybe not for much longer!)i was talking about the run of the mill cars.Does the gt2 share same engine has turbo G2 if so dfi!

[Martian O]

mayes911 said:

....Does the gt2 share same engine has turbo G2 if so dfi!

No, they're different.

[Akajak]

those of a nervous disposition look away

http://www.planet-9.com/cayman-boxster-chat/32256-...

[sbirty]

If this a becomes a real problem with porsche DFI engines and products like seafoam really work won't OPC build that treatment into their 2 yearly service schedules??

Edited by sbirty on Wednesday 1st December 19:18

[Ian_UK1]

sbirty said:

If this a becomes a real problem with porsche DFI engines and products like seafoam really work won't OPC build that treatment into there 2 yearly service schedules??

Unfortunately, products like Seafoam don't work at all. Have a read on t'Internet - there are engineering shops that have tried soaking badly carbon'd inlet valves in chemical solvents overnight with no result - this stuff has to virtually be ground off. A product like Seafoam (and there are others that just as falsely claim to clean valves) that is in contact with the carbon deposits for a few millisconds won't do jack st!

In simple terms, there is no quick fix for oil deposits that have been baked solid onto the backs of the inlet valves. All you can do is strip the engine and machine the parts clean.

What we need to find out is how quickly these deposits build-up, at what point they start to really mess with the engine's performance and by how much that performance will ultimately suffer. That way we'll know when the decoke bills will start to arrive - hopefully it will be well into the life of the engine (but it could just as easily be early in its life, as was the case with Audi motors).

Ian

Edited by Ian_UK1 on Friday 12th November 17:40

[Martian O]

As I mentioned above, I had a Mitsubishi DFI engine with these problems at 20K miles. They used a shot-blast method using walnut shells. The car ran really rough until it was done, never another DFI engine, or until they at least get over this problem.

[Wills2]

Ian_UK1 said:

sbirty said:

If this a becomes a real problem with porsche DFI engines and products like seafoam really work won't OPC build that treatment into there 2 yearly service schedules??

Unfortunately, products like Seafoam don't work at all. Have a read on t'Internet - there are engineering shops that have tried soaking badly carbon'd inlet valves in chemical solvents overnight with no result - this stuff has to virtually be ground off. A product like Seafoam (and there are others that just as falsely claim to clean valves) that is in contact with the carbon deposits for a few millisconds won't do jack st!

In simple terms, there is no quick fix for oil deposits that have been baked solid onto the backs of the inlet valves. All you can do is strip the engine and machine the parts clean.

What we need to find out is how quickly these deposits build-up, at what point they start to really mess with the engine's performance and by how much that performance will ultimately suffer. That way we'll know when the decoke bills will start to arrive - hopefully it will be well into the life of the engine (but it could just as easily be early in its life, as was the case with Audi motors).

Ian

Edited by Ian_UK1 on Friday 12th November 17:40

Ian, if you are so concerned regarding this then go get your engine scoped and post up the pictures? until then its all hear say and internet talk.

Proof is what we need and as a fellow gen2 owner with 33k on his I would be interested to see the issue if it does infact exist in our engines.

I've seen the pics of the cayenne etc but never one of a gen2 911.

Cheers


Wills.

Edited by Wills2 on Friday 12th November 17:49

[bcnrml]

Wills2 said:

Ian, if you are so concerned regarding this then go get your engine scoped and post up the pictures? until then its all hear say and internet talk.

Proof is what we need and as a fellow gen2 owner with 33k on his I would be interested to see the issue if it does infact exist in our engines.

I've seen the pics of the cayenne etc but never one of a gen2 911.

Cheers


Wills.

Edited by Wills2 on Friday 12th November 17:49

Friendly note: Why not take a leaf out of your own book and get yours looked at, posting up the pictures? You'd provide a helpful counter to (or support for) Ian_UK1's points, those points based on the experience of probably every engine manufacturer in the world.

Maybe your pictures would help with the theory you're promoting: That somehow, Porsche (troubled and allegedly very skint Porsche, that is) found a solution to avoid coke on DFi engines, something no other engine manufacturer has for yonks.

Ian_UK1 has provided a technically competent description of the problem which has been corroborated by others elsewhere and helpfully discussed online. You haven't, but you keep saying it is hearsay.

I remember when the following were hearsay:

RMS (fixed for more than ten years now),
IMS (never happened at one time, y'see)
Cracked liners (never happened at one time, y'see)
Seizing on banks 4,5,6 (never on a 997, never)

One company gave us all of the above. Said company was once capable of easily fixing (once and for all) all of those engine traits. The same company, I suspect in your view, has found a secret solution to coke and DFi engines that it is refusing to license to others, keeping said secrets for the most faithful die-hard (blinkered, rose tinted spec-wearing) porker pilots in the UK.

Just because you haven't seen it on a 997 doesn't mean it doesn't exist.

[betternotbigger]

Porsche in "Cars don't perform as well and even need extra maintenance when they get older" shock!!!

Could this be part of the reason why they cost more new?

You pays your money and takes your choice...

Edited by betternotbigger on Saturday 13th November 07:32

[drmark]

Not one reported case in a 997 = no problem yet. One case, plus troubles with other DFI engines = cause for concern and should prompt further investigation. Lots of cases = major problem.
Until we hear of the first case in a 997 I would ignore the sort of hype created on here. Nothing more useless than worrying about something that may never happen.


Edited to add: I have a GT3 so have no vested interest in this debate. And don't forget, despite what you may read on here - some of it propagated by people who don't even own a Porsche and are basing all their doom mongering on second hand info - Porsches are the most reliable high performance sports cars out there ( with the possible exception of the NSX), and owning one is generally a very rewarding experience. Just enjoy your car.

Edited by drmark on Saturday 13th November 08:45

[Wills2]

bcnrml said:

Wills2 said:

Ian, if you are so concerned regarding this then go get your engine scoped and post up the pictures? until then its all hear say and internet talk.

Proof is what we need and as a fellow gen2 owner with 33k on his I would be interested to see the issue if it does infact exist in our engines.

I've seen the pics of the cayenne etc but never one of a gen2 911.

Cheers


Wills.

Edited by Wills2 on Friday 12th November 17:49

Friendly note: Why not take a leaf out of your own book and get yours looked at, posting up the pictures? You'd provide a helpful counter to (or support for) Ian_UK1's points, those points based on the experience of probably every engine manufacturer in the world.

Maybe your pictures would help with the theory you're promoting: That somehow, Porsche (troubled and allegedly very skint Porsche, that is) found a solution to avoid coke on DFi engines, something no other engine manufacturer has for yonks.

Ian_UK1 has provided a technically competent description of the problem which has been corroborated by others elsewhere and helpfully discussed online. You haven't, but you keep saying it is hearsay.

I remember when the following were hearsay:

RMS (fixed for more than ten years now),
IMS (never happened at one time, y'see)
Cracked liners (never happened at one time, y'see)
Seizing on banks 4,5,6 (never on a 997, never)

One company gave us all of the above. Said company was once capable of easily fixing (once and for all) all of those engine traits. The same company, I suspect in your view, has found a secret solution to coke and DFi engines that it is refusing to license to others, keeping said secrets for the most faithful die-hard (blinkered, rose tinted spec-wearing) porker pilots in the UK.

Just because you haven't seen it on a 997 doesn't mean it doesn't exist.

If you read my post properly I'm not promoting any theory just asking for evidence from people such as yourself who are promoting the theory that the gen2 DFI engine suffers from coking.

I haven't said it does or it doesn't, I have merely asked for more than internet chat and pictures of other cars.

I have no rose tinted glasses about my car or Porsche for that matter.

And I'm fully aware that absence of evidence isn't evidence of absence.

[bcnrml]

Wills2 said:

If you read my post properly I'm not promoting any theory just asking for evidence from people such as yourself who are promoting the theory that the gen2 DFI engine suffers from coking.

Yet earlier,

Wills2 said:

Proof is what we need and as a fellow gen2 owner with 33k on his I would be interested to see the issue if it does infact exist in our engines.

I read your post properly (and I am functionally literate).

All the evidence I've seen points to all manufacturers having problems with coking on direct DFI type engines. Can you provide any evidence to help change my view (said view corroborated with evidence on the internet)? I'm happy to be proven wrong. Provide the links to do so. For his side of the debate, Ian_UK1 has already gone far beyond your own input. I do not own any cars with this engine design (never have), so I don't care from a financial or performance perspective. They're only ever in my hands when they're loaners, and I’m always happy to hand them back (as I did with one on Thursday evening).

Porsche's 15 year history on engines hardly inspires one with confidence. On Ian_UK1's aforementioned thread, I enquired about the DFI in the naive hope that the problem would be minor and I got excellent technical responses that were an education. With evidence.

Wills2 said:

I haven't said it does or it doesn't, I have merely asked for more than internet chat and pictures of other cars.

There's plenty of evidence. Go to Ian_UK1's original thread (do a search) and build your research from there. Educate me: Is the Cayenne engine referred to completely different to yours?

Wills2 said:

I have no rose tinted glasses about my car or Porsche for that matter.

Good. You may not, but there are many others who do, and I think that if you cannot counter the technical analysis (and evidence on here) with arguments of the same standard, you've a responsibility to other porker nuts (aspirants, owners and indeed the less knowledgeable members of the trade) to stop dismissing this kind of thing as internet chat. Global FMCG companies, investment bankers, hedge funds, private equity firms, market analysts and some of the best journalism is based on so-called internet chatter followed by some due diligence. This forum remains amazing in that people will come on here and use the phrase “internet chat” or “internet hearsay” to dismiss a well-argued set of points that are designed to help fellow porkers!

Wills2 said:

And I'm fully aware that absence of evidence isn't evidence of absence.

Good. That’s how I live.

So will you match Ian-UK1's offer in your own way? Why don't you do exactly what you asked him to do? In fact, why don't you all (owners of DFI engined porkers) ask your OPCs (and/or Indies) to give you the evidence? That'd be helpful for all concerned (I imagine the OPCs cannot lose either way so they should be helpful). You might prove this is a myth. You might corroborate it. Just getting pictures - as you yourself noted - would be very helpful.

So, Wills2, please just say when and start a new thread with your pics. That's fair and reasonable, no? Ian_UK1's made an open offer already. Any other takers?

Edited by bcnrml on Saturday 13th November 13:14

[Ian_UK1]

...and I'll stick to the open offer I made. I live within 20 minutes or so of Hartech and would certainly trust them to inspect the inlet valves in my engine assuming (as I'm sure they do) they have the equipment to make this possible.

The problem with asking any engineering shop however, is that I can't see any incentive for them to offer to look. To do an inspection of this type is time consuming and wouldn't offer any immediate benefit to the firm undertaking the work. From my own perspective, I don't particularly want to spend my own money researching this unless it goes hand in hand with being able to provide a solution - assuming an issue exists!

To clarify again my position on the whole issue of carbon build-up - no I haven't seen direct evidence of this in a 997 DFI engine. However, this engine doesn't differ in its fundamentals from other DFI engines - it still uses a crankcase re-breather with an oil separator, it still has fuel injectd directly into the cylinders, the inlet valves and ports aren't washed or cooled by incoming fuel. So why should this engine be any different to other DFI engines? Carbon build-up will happen, what we don't know is how much and how quickly. What we also don't know is the effect on power outputs. The latter could only be quamtified by dynoing a single car immediately after break-in, then every x-thousand miles or so (the interval being dependent on how quickly the carbon deposits build-up) and graphing the results over time.

Yes, I agree that we don't have all the information we need yet. However, that doesn't mean the engines don't suffer from carbon build-up, just like all DFIs and Diesels!!

Ian

Edited by Ian_UK1 on Saturday 13th November 14:42

[Pesty]

lynchygt3 said:

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

Thats true so the first owner after running in should take the car to two independant dyno places that use different types of dyno.

The date time temperature and humidaty should be noted. 3 years down the line when they want to sell they should take their cars back to the same places in the same conditions and use the same correction factors to see if their engines are full of carbon